Constituents

The BP/EP requires a minimum concentration of 0.1% for the steam volatile fraction of Meadowsweet; the flowers have recorded higher values. The major component of the oil (up to ca 70%) is salicylaldehyde (Fig. 21.1) together with methyl salicylate, benzaldehyde, benzyl alcohol, and smaller amounts of other components such as vanillin. In 1839, Löwingand and Weidmann, working on meadowsweet, were the first to report salicylic acid as a natural product. Other constituents of the drug are the phenolic glycosides gaultherin (Table 21.1) and spiraein (salicyl alcohol + primerose), various flavonoids, e.g. hyperoside (Fig. 21.18), tannins and mucilage.

Fig. 21.1 Simple phenolic compounds.

The pharmacopoeial TLC test for identity indicates the required presence of methyl salicylate and salicylaldehyde in the test sample. The permitted maximum for stems with a diameter greater than 5 mm is 5% and for foreign matter, 3%.

Action and uses

The BP/EP cites meadowsweet as a diuretic; traditionally it has also been used for its anti-inflammatory, astringent and stomachic properties.

History

Vanilla was found in Mexico by the Spaniards, where it was used for flavouring chocolate, a use to which it is still put. It found a place in the London Pharmacopoeia of 1721.

Cultivation

Vanilla requires a warm and fairly moist climate. Propagation is simple: cuttings 1–3 m long are attached to trees (e.g. Casuarina equisetifolia), where they soon strike roots on the bark. The plant is an epiphyte. It flowers at the end of 2 or 3 years and continues to produce fruit for 30–40 years. The flowers are usually pollinated by women and children, a pointed stick being introduced into one flower after another. Clonal propagation of the vanilla plant has been described together with in vitro multiplication using axillary bud explants (P. S. George and G. A. Ravishankar, Plant Cell Rep., 1997, 16, 490).

Collection and curing

The fruits are collected when the upper part of the pod changes in colour from green to yellow. The characteristic colour and odour of the commercial drug are only developed as a result of enzyme action during the curing. The details of the latter process vary somewhat in different countries, but frequently it consists of slow drying in sheds which are kept at carefully regulated temperatures.

Packing and grading

Before grading, any pods showing a tendency to mould are picked out. The remainder are sorted to size and packed in bundles of 50 pods. Traditionally, these were packed in tin cases or boxes holding about 10–12 kg, soldered up and packed in wooden cases. On arrival in London the tins were opened and the pods were examined. UK supplies now arrive via France or Germany, with some from Madagascar. During storage crystals frequently develop on the surface of the pods.

Characters

Vanilla pods are 15–25 cm long, 8–10 mm diameter and somewhat flattened. The surface is longitudinally wrinkled, dark brown to violet-black in colour, and frequently covered with needle-like crystals of vanillin (‘frosted’). The fruits are very pliable and have a very characteristic odour and taste.

Constituents

Green vanilla contains glycosides, namely glucovanillin (vanilloside) and glucovanillic alcohol. During the curing these are acted upon by an oxidizing and a hydrolysing enzyme which occur in all parts of the plant. Glucovanillic alcohol yields on hydrolysis glucose and vanillic alcohol; the latter compound is then by oxidation converted into vanillic aldehyde (vanillin). Glucovanillin, as its name implies, yields on hydrolysis glucose and vanillin (Fig. 21.4).

Fig. 21.4 Constituents of vanilla.

The three species given above differ in their relative contents of anisyl alcohol, anisaldehyde (also anisyl ethers and anisic acid esters), piperonal and p-hydroxybenzoic acid. These minor components, together with the two diastereoisomeric vitispiranes, add to the flavour of the pods.

Vanillin BP/EP

Vanillin BP is the aldehyde corresponding to methyl-protocatechuic acid and has been synthesized in a number of ways. Large quantities of it are prepared from eugenol isolated from oil of cloves (q.v.) or from guaiacol (methyl catechol). It can also be produced by microbial oxidation of eugenol. In the plant glucovanillin is biosynthesized via ferulic acid (see Fig. 21.2). Synthesis begins when elongation of the fruit ceases, which is about 8 months after pollination; before this, other phenolic glycosides predominate.

Adulteration

Extracts of Mexican origin may be adulterated by coumarin, probably arising from the use of tonka beans (q.v.). A capillary GC assay has been described for such products (see R. J. Marles et al., Economic Bot., 1987, 41, 41).

Uses

Vanilla pods are widely used in confectionery and in perfumery. They have been replaced to some extent, but by no means completely, by synthetic vanillin. About 0.07 parts of vanillin are approximately equivalent to 1 part of the bean, but an essence so prepared fails to represent the odour and flavour of the whole pods.

For a review of natural vanillin, covering biosynthesis, biotechnological production, cell and organ culture and metabolic engineering, see N. J. Walton et al., Phytochemistry, 2003, 63, 505–515.

History

Capsicums appear to be of American origin and were referred to in 1494 by Chanca, a physician who accompanied Columbus on his second voyage to the West Indies. The plants were introduced into India at a very early date, possibly by the Portuguese. ‘Ginnie Pepper’ was well known in England in 1597 and was grown by Gerarde.

Macroscopical characters

African Chillies are oblong-conical in shape, 12–25 mm long and up to 7 mm wide. The five-toothed calyx and straight pedicel are together about 20–30 mm long. The pericarp is glabrous, shrivelled and orange-red; the Sierra Leone and Zambian chillies usually have a better colour than those from Zanzibar.

Internally the fruits are divided into two cells by a membranous dissepiment to which the seeds were originally attached. The latter, usually about 10–20 in each fruit, are of a flattened reniform shape and are about 3–4 mm long. Like other solanaceous seeds, they have a coiled embryo and oily endosperm. African chillies are very sternutatory and have an intensely pungent taste.

Constituents

In 1876, Thresh extracted the drug with petroleum, treated the extract with aqueous alkali, and by passing carbon dioxide through the alkaline liquid precipitated crystals of an intensely pungent compound, capsaicin. As may be inferred from the method of preparation, capsaicin is of phenolic nature.

The pungent phenolic fraction of capsicum also contains a proportion of 6,7-dihydrocapsaicin. The capsaicin content of fruits varies appreciably in a range up to 1.5% and is much influenced by environmental conditions and age of the fruit. It occurs principally in the dissepiments of the fruits—for example, entire fruit 0.49, pericarp 0.10, dissepiment 1.79, seed 0.07. The pungency of capsicum is not destroyed by treatment with alkalis (distinction from gingerol, which also contains the vanillyl group) but is destroyed by oxidation with potassium dichromate or permanganate. Chillies also contain ascorbic acid (0.1–0.5%), thiamine, red carotenoids such as capsanthin and capsorubin (see ‘Carotenoids’) and fixed oil (about 4–16%). They yield about 20–25% of alcoholic extract (capsicin) and about 5% (official limit 10.0%) of ash. Hungarian capsicums or ‘Paprika’ are derived from a mild race of C. annuum and are a convenient source of ascorbic acid. According to Bennett and Kirby, the pungent principle of C. annuum is composed of capsaicin 69%, dihydrocapsaicin 22%, nordihydrocapsaicin 7%, homocapsaicin (C₁₁ acid) 1% and homodihydrocapsaicin 1%. A number of minor components of this class have been recorded.

In a study of the water-soluble constituents of the fruits of three varieties of C. annuum, Izumitani et al. (Chem. Pharm. Bull., 1990, 38, 1299) isolated twelve novel acyclic glycosides (geranyllinalool derivatives) named capsianosides A–F (dimeric esters of acyclic diterpene glycosides) and capsianosides I–V (monomeric compounds of acyclic diterpene glycosides). Further capsianosides have now been reported by J.-H. Lee et al., (Chem. Pharm. Bull., 2006, 54, 1365). T. Ochi et al., (J. Nat. Prod., 2003, 66, 1094) record a dimeric capsaicin having almost the same antioxidant activity as capsaicin but with no pungent taste (Fig. 21.5).

Fig. 21.5 Some constituents of capsicum.

Biogenesis of capsaicin

Work by Leete and Louden on C. frutescens and by Bennett and Kirby on C. annuum demonstrated that phenylalanine is incorporated into the C₆–C₁ vanillyl unit of capsaicin, the C-3 of phenylalanine giving the methylene group of the vanillylamine residues; the incorporation probably proceeds via cinnamic, p-coumaric, caffeic and protocatechuic acids. Tyrosine did not appear to be a probable precursor. Leete’s feeding experiments with [U-¹⁴C]-valine gave incorporations consistent with the hypothesis that the C₁₀ isodecanoic acid is formed from isobutyryl coenzyme A and three acetate units. More recent work showed that the homo derivatives (C₁₁ acid) are formed from leucine and isoleucine.

The ontogenetic formation of capsaicinoids in the fruits of C. frutescens involves a prior active accumulation of p-coumaroyl, caffeoyl and 3,4-dimethoxycinnamoyl glycosides, 3-O-rhamnosylquercetin and 7-O-glucosylluteolin. When the fruit ceases to increase in length the amount of these compounds falls and capsaicinoid synthesis commences together with that of the glycosides of vanillic acid and p-hydroxybenzaldehyde (see N. Sukrasno and M. M. Yeoman, Phytochemistry, 1993, 32, 839).

Cell cultures

The biogenetic potential for capsaicin production is reported (1991) as 10 times greater in immobilized cell cultures (alginate entrapment) than in control suspension cultures.

Tests and standards

The official TLC test for identity establishes the presence of capsaicin and dihydrocapsaicin in the sample. The synthetic equivalent of capsaicin, nonivamide (pelargonyl vanillylamide), a commercial product used as a flavour in the food industry and in medicine as a topical rubifacient, is limited by a liquid chromatographic assay to a maximum of 5% of the total capsaicinoid content. Liquid chromatography is also used to determine the total capsaicinoid content (minimum 0.4%). A number of colorimetric assays can be used for the quantitative determination of capsaicin (see Table 16.5); the BPC 1973 utilized ultraviolet absorption at 248 and 296 nm for the ointment and oleoresin. Foreign matter should not exceed a maximum of 2%; fruits of C. annuum L. var. longum (Sendtn.) (see ‘Bombay capsicums’ below) should be absent.

Allied drugs

Japanese Chillies are probably derived from C. frutescens and are about 3–4 cm long. They possess about one-quarter of the pungency of the African Chillies, but are now no longer commercially relevant.

Bombay Capsicums are ascribed to C. annuum L. The pericarp is thicker and tougher than in the chillies, and the pedicel is frequently bent. They are much less pungent than African chillies.

Natal Capsicums are larger than the Bombay variety, being up to 8 cm long. They have a very bright red, transparent pericarp. They are much less pungent than chillies.

Uses

Capsicums are used as a condiment under the name of Cayenne pepper. The drug is given internally in atonic dyspepsia and flatulence. It is used externally as a counter-irritant, in the form of ointment, plaster, medicated wool, etc., for the relief of rheumatism, lumbago, etc. Capsaicin creams are available for the relief of pain in osteoarthritis, post-herpetic neuralgia and painful diabetic neuropathy (Pharm. J., 1998, 260, 692).

Occurrence of tannins

Tannins are of wide occurrence in plants and are usually found in greatest quantity in dead or dying cells. They exert an inhibitory effect on many enzymes due to protein precipitation and, hence, they may contribute a protective function in barks and heartwoods. Commercial tannins, as used in the leather industry, are obtained from quebracho, wattle, chestnut and myrobalans trees. Pharmaceutical tannin is prepared from oak galls (q.v.) and yields glucose and gallic acid on hydrolysis; many commercial samples contain some free gallic acid.

Some plants (clove, cinnamon, etc.) contain tannin in addition to the principal therapeutic constituents. This may complicate extraction or produce incompatibilities with other drugs (many alkaloids, for example, are precipitated by tannins).

Properties and tests

Tannins are soluble in water, dilute alkalis, alcohol, glycerol and acetone, but generally only sparingly soluble in other organic solvents. Solutions precipitate heavy metals, alkaloids, glycosides and gelatin. With ferric salts, gallitannins and ellagitannins give blue-black precipitates and condensed tannins brownish-green ones. If a very dilute ferric chloride solution is gradually added to an aqueous extract of hamamelis leaves (which contains both types of tannin), a blue colour is produced which changes to olive-green as more ferric chloride is added. Other tests are the following.

In practice, these tests have to some extent been superseded by the use of TLC, particularly for the identification of crude drugs.

Medicinal and biological properties

Tannin-containing drugs will precipitate protein and have been used traditionally as stypics and internally for the protection of inflamed surfaces of mouth and throat. They act as antidiarrhoeals and have been employed as antidotes in poisoning by heavy metals, alkaloids and glycosides. In Western medicine their use declined after World War II when it was found that absorbed tannic acid can cause severe central necrosis of the liver. Recent studies have concentrated on the antitumour activity of tannins (M. Ken-ichi et al., Biol. Pharm. Bull., 1993, 16, 379) and it has been shown that, to exhibit a strong activity, ellagitannin monomer units having galloyl groups at the O-2 and O-3 positions on the glucose core(s), as in the tellimagrandins (Fig. 21.6) are required. Anti-HIV activity has also been demonstrated.

Proanthocyanidins (condensed tannins) are associated with the beneficial effects of various herbs and infusions produced from them. The antitumour activity of green and black tea has been extensively researched in recent years with positive findings. Of the components of tea, epigallocatechin-3-gallate, specifically, has been shown to prevent angiogenesis in mice. Cranberry juice has long been used for reducing bacterial infections of the bladder and these claims have now been supported by a randomized, double-blind, placebo-controlled trial carried out on 153 elderly women (J. Avorn et al., J. Amer. Med. Assoc., 1994, 271, 751). Fructose has been implicated in this activity but recently, proanthocyanidins prepared from cranberries by reverse-phase and adsorption chromatography were shown to inhibit the adherence of P-fimbriated E. coli to uroepithelial-cell surfaces; other Vaccinium spp., including blueberries had similar bioactivity, suggesting their contribution to the salutary effects in urinary tract infections (A. Howell et al., New Engl. J. Med., 1998, 339, 1085).

History

Galls were well known to the ancient writers and Pliny records the use of their infusion as a test for sulphate of iron in verdigris, possibly the earliest mention of an attempt to detect adulteration by chemical means.

Characters

Aleppo galls are globular in shape and from 10 to 25 mm in diameter. They have a short, basal stalk and numerous rounded projections on the surface. Galls are hard and heavy, usually sinking in water. The so-called ‘blue’ variety are actually of a grey or brownish-grey colour. These, and to a lesser extent the olive-green ‘green’ galls, are preferred to the ‘white’ variety, in which the tannin is said to have been partly decomposed. White galls also differ from the other grades in having a circular tunnel through which the insect has emerged. Galls without the opening have insect remains in the small central cavity. Galls have a very astringent taste.

Sections through a gall show a very large outer zone of thin-walled parenchyma, a ring of sclerenchymatous cells, and a small, inner zone of rather thick-walled parenchyma surrounding the central cavity. The parenchymatous tissues contain abundant starch, masses of tannin, rosettes and prisms of calcium oxalate, and the rounded so-called ‘lignin bodies’, which give a red colour with phloroglucinol and hydrochloric acid.

Constituents

Galls contain 50–70% of the tannin known as gallotannic acid (Tannic Acid BP/EP); this is a complex mixture of phenolic acid glycosides varying greatly in composition. It is prepared by fermenting the galls and extracting with water-saturated ether. Galls also contain gallic acid (about 2–4%), ellagic acid, sitosterol, methyl betulate, methyl oleanolate, starch and calcium oxalate. Two new compounds, derivatives of ellagic acid and pentahydroxynaphthalene, isolated from the alcoholic extract of galls have been shown to have nitricoxide- and superoxide-inhibiting activity (H. Hamid et al., Pharm. Biol., 2005, 43, 317). Nyctanthic, roburic and syringic acids have more recently been identified and syringic acid has been identified as the CNS-active component of the methanolic extract of galls. (For the isolation of flavonoids of oak galls see M. Ahmed et al., Fitoterapia, 1991, 62, 283.)

Tannic acid is a hydrolysable tannin (see above) yielding gallic acid and glucose and having the minimum complexity of pentadigalloyl glucose. Solutions of tannic acid tend to decompose on keeping with formation of gallic acid, a substance which is also found in many commercial samples of tannic acid. It may be detected by the pink colour produced on the addition of a 5% solution of potassium cyanide.

Allied drugs

Many different kinds of galls are known. They are generally produced on plants, but sometimes on animals. In addition to the large number produced by insects, particularly of the genera Cynips and Aphis, some are produced by fungi.

Chinese and Japanese galls are of considerable commercial importance. They are produced by an aphis, Schlectendalia chinensis, on the petioles of the leaves of Rhus chinensis (Anacardiaceae). These galls, which the Chinese call ‘wu-pei-tzu’, meaning ‘five knots’, are irregular in shape and partly covered with a grey, velvety down, the removal of which discloses a reddish-brown surface. They break easily and show a large, irregular cavity containing insect remains. They contain 57–77% of tannin and have been valued in China as astringents and styptics for at least 1250 years.

Crowned Aleppo galls are sometimes found in samples of ordinary Aleppo galls. They are about the size of a pea, are stalked, and bear a crown of projections near the apex. The insect producing them is Cynips polycera.

Hungarian galls are produced by Cynips lignicola on Quercus robur growing in former Yugoslavia. They are used in tanning. English oak galls, formed by Adleria kollari on Quercus robur, contain about 15–20% of tannin.

Uses

Galls are used as a source of tannic acid, for tanning and dyeing, and in the manufacture of inks. Tannic acid is used as an astringent and styptic.

Macroscopical characters

The leaves are shortly petiolate, 7–15 cm long, and broadly oval to ovate in shape; base asymmetrically cordate, apex acute. The lamina is dark brownish-green to green in colour and very papery in texture. The venation is pinnate and the margin crenate or sinuate-dentate. The veins are very conspicuous on the lower surface; they leave the mid-rib at an acute angle and run straight to the margin, where they terminate in a marginal crenation. Odour, slight; taste, astringent and bitter.

The BP/EP drug is required to contain not more than 7% of stems and not more than 2% of other foreign matter.

Microscopical characters

The drug has very distinctive microscopical characters. These include characteristic stomata present on the lower surface only; very large lignified idioblasts, crystal cells accompanying the pericyclic fibres, tannin-containing cells and, especially in young leaves, stellate hairs. The calcium oxalate is in monoclinic prisms 10–35 μm long. The stellate hairs (Fig. 42.1H) consist of 4–12 cells united at the base. Each cell is thick-walled and up to 500 μm long.

Constituents

Hamamelis contains gallitannins, ellagitannins, free gallic acid, proanthocyanidins, bitter principles and traces of volatile oil. With ferric chloride solution the gallitannins and the free gallic acid give a blue colour and the ellagitannins, green.

The pharmacopoeia requires the leaves to contain not less than 3.0% tannins; these tannins represent the difference between the total poly-phenol content of the leaf and the polyphenol content not absorbed by hide powder. Reagents employed in the assay are Phosphomolybdotungstic reagent and sodium carbonate solution with absorbance measurements made at 760 nm; pyrogallol is used as a test solution. The leaves appear to contain no hamamelitannin (see ‘Hamamelis Bark’, below).

Volatile compounds, although present in small amounts only, have been studied by GC-MS analysis. Some 175 compounds have been distinguished and classified as homologous series of alkanes, alkenes, aliphatic alcohols, related aldehydes, ketones and fatty acid esters; distinctive monoterpenoids were evident (R. Engel et al., Planta Medica, 1998, 64, 251).

A procedure for the identification and assay involving TLC, HPLC, plate densitometry and spectrophotometry for the proanthocyanidins, phenolic acids and flavonoids in leaf extracts has been described (B. Vennat et al., Pharm. Acta Helv., 1992, 67, 11).

Allied drugs

Hamamelis bark occurs in curved or channelled pieces which seldom exceed 10 cm long or 2 cm wide. The bark is silvery grey and smooth, or dark grey and scaly. The inner surface is pinkish and often bears fragments of whitish wood. Sections show a cortex containing prismatic crystals of calcium oxalate, a complete ring of sclerenchymatous cells, and groups of phloem fibres. The bark contains a mixture of hamamelitannin and condensed tannin; the former has recently been demonstrated to be a potent oxygen scavenger (H. Masaki et al., Phytochemistry, 1994, 37, 337). Three separate hamamelitannins, α-, β- and γ-, are now known. The most important, β-hamamelitannin, is formed from two gallic acid molecules and one molecule of the sugar hamamelose. Newer galloylhamameloses and proanthocyanidins have now been identified (C. Haberland and H. Kolodziej, Planta Medica, 1994, 60, 464; C. Hartisch and J. Kolodziej, Phytochemistry, 1996, 42, 191). For the fractionation of those polymeric proanthocyanidins having similar structures but different molecular weights, see A. Dauer et al., Planta Med., 2003, 69, 89.

Uses

Hamamelis owes its astringent and haemostatic properties to the tannins. Hamamelitannin and the galloylated proanthocyanidins isolated from H. virginiana are reported to be potent inhibitors of 5-lipo-oxygenase, supporting the anti-inflammatory action of the drug (C. Hartisch et al., Planta Medica, 1997, 63, 106). The above compounds are presumably not present in Hamamelis Water or Distilled Witch Hazel, which is, however, widely used as an application to sprains, bruises and superficial wounds and as an ingredient of eye lotions. It contains safrole and other volatile components.

Constituents

The rhizome contains a mixture of both hydrolysable and condensed tannins (proanthocyanidins). Among the former is agrimoniin, a dimeric ellagitannin found also in Agrimonia and Alchemilla, and belonging to the same biosynthetic group, ellagic acid and catechol gallates. Other components are flavan-3-ols, the pseudosaponin tormentoside, quinovic acid and various phenylpropanes together with a trace of volatile oil.

Standards

BP/EP requirements are a minimum of 7.0% tannins calculated as pyrogallol for the dried rhizome. A maximum of 3% for roots, stems and rhizomes with a black fracture. Other foreign matter limited to 2%. Compliance with a TLC test for identity using catechin as a reference substance.

Uses

As an astringent; internally as an antidiarrhoeic and externally for gargles and inflamed mucous membranes.

Characters

Characteristic of a number of genera of the family Rosaceae, so-called hawthorn berries are false fruits (pomes, and not in the strict botanical sense berries) in which the carpels become adherent to the hollow, fleshy receptacle and the sepals, petals and stamens become situated at the upper end of the fruit. The carpels become stony so that the pome comes rather to resemble a drupe (Ch. 41). The false fruits of C. monogyna with one carpel contain a single stony true fruit whereas those of C. laevigata with two or three carpels contain two or three fruits.

The dried reddish-brown to dark red fruits have a slight odour and mucilaginous, slightly acid taste; with C. monogyna they are up to 10 mm in length and slightly larger for C. laevigata. At the upper end of the false fruit are the remains of the five reflexed sepals which surround a shallow depression from the base of which arise stiff lignified tufts of trichomes and the remains of the style (two styles with C. laevigata). The base of the fruit may be either attached to a pedicel or show the scar of attachment of the latter.

In addition to the long, lignified, tapering clothing trichomes of the inner surface of the receptacle other microscopical features include: cells of the outer receptacle with red pigmentation; sclereids; calcium oxalate as clusters and in files of cells as prisms; seed fragments showing a mucilaginous testa and embryo cells containing aleurone grains and fixed oil. A more detailed description will be found in the pharmacopoeias.

Constituents

The fruits contain 1–3% oligomeric procyanidins, the structures of which appear to be only partially ascertained together with flavonoids, principally hyperoside about 1%. The leaves in contrast contain less hyperoside and more vitexin rhamnoside.

Thin layer chromatography of a methanolic extract of the drug and fluorescence visualization at 365 nm is used as a test for identity. Procyanidins are evaluated by acid hydrolysis of an alcoholic extract followed by absorbance measurements at 545 nm of the butanol-soluble procyanidins produced.

The leaves and flowers, in contrast to the fruits, contain less hyperoside and more vitexin rhamnoside. In a study of important factors for the use of monitored commercial material, W. Peschel et al. (Fitoterapia, 2008, 79, 1) have examined the variability of total flavonoid content of the drug in relation to wild trees, age of cultivation site, sun exposure and harvest time.

Allied species

Adulteration of the readily available product is rare; other species of Crataegus may be detected by their having more than three seeds. C. pinnatifida fruits are used in Chinese medicine.

Uses

Hawthorn is widely used as a mild cardiac tonic particularly for patients of advancing age. It does not have the toxic effects of Digitalis and can usefully be employed before recourse is made to the digitalis cardioactive glycosides.

Allied species

The roots of several other species are occasionally encountered in commerce, but the Peruvian drug is the only one generally available. Krameria cystisoides of Mexican origin has indigenous medicinal uses. It contains over 20 compounds of the lignan, neolignan and norneolignan type. Similar constituents are reported for K. lanceolata; see H. Achenbach et al., Phytochemistry, 1987, 26, 1159; 1989, 28, 1959.

History

The catechu described by Barbosa (1514) was black catechu or cutch, and the first account of gambir appears to be that of a Dutch trader in 1780. In addition to the cube gambir used in pharmacy, large blocks of the extract are imported for use in dyeing and tanning. Other forms are used in the East for chewing with betel leaf.

Preparation

The preparation of catechu in Johore differs only slightly from the procedure adopted in Indonesia. It consists of extracting the leaves and young twigs with boiling water, evaporating the extract to a pasty consistency and dividing it into cubes, which are then sun-dried. Fuller details of the preparation are given in the 10th edition.

Many different forms of catechu are used in the East, and the drug for the Eastern market frequently has 20–50% of fine rice husks added as the liquid coagulates in the tubs. Such catechu is, of course, unofficial, and contains starch.

Macroscopical characters

Catechu occurs in cubes, which are very friable and may be broken up in transit or, if incompletely dried, may be more or less agglutinated. Of the samples available, those from Indonesia measure 17–22 mm and have a reddish-brown surface, often stamped with a maker’s mark, while those from Johore measure 24–29 mm and have a blackish exterior and the faces of the cube are depressed. Internally, both varieties are cinnamon-brown and porous. Odourless; taste, very astringent and at first somewhat bitter, afterwards sweetish.

Microscopical characters

When mounted in water, catechu shows minute, acicular crystals of catechin, many of which are branched and interlacing. They dissolve on warming and a considerable amount of vegetable debris is left. The leaves, particularly the stipules, bear simple, unicellular hairs up to about 350 mu;m long, with smooth, moderately thick, lignified walls. The twigs have lignified pericyclic fibres, wood fibres, and spiral, annular and pitted vessels. Minute starch grains are commonly present, particularly in the Indonesian drug, but the amount should be strictly limited. Rice husks have been observed in some samples.

Chemical tests

Constituents

Gambir contains about 7.33% of catechins, 22–50% of catechutannic acid, catechu red, quercitin and gambir-fluorescin.

BP (Vet.) 2007 standards include a loss on drying of not more than 15.0% and a water-insoluble matter of not more than 33.0% with reference to the dried material.

Catechin forms white, acicular crystals which are soluble in hot water and alcohol and give a green colour with ferric salts. Catechutannic acid is an amorphous phlobatannin which appears to be formed from catechin by loss of the elements of water. It readily yields the phlobaphene catechu-red. If the drug is carefully prepared, it will contain a high proportion of catechin and correspondingly smaller amounts of catechutannic acid and catechu-red.

Allied drug

Cutch or black catechu is an extract prepared from the heartwood of Acacia catechu (Leguminosae). Cutch occurs in black, somewhat porous masses. The taste resembles that of gambir. Microscopical examination of the water-soluble residue shows wood fibres and large vessels and sometimes fragments derived from the leaves on which the drug is spread.

Cutch contains 2–12% of catechins, 25–33% of phlobatannin, 20–30% of gummy matter, quercitrin, quercitin, moisture, etc. It yields 2–3% of ash. The catechin (acacatechin) is not identical with that in gambir. The drug may be distinguished from gambir as it gives no reaction for gambir-fluorescin.

Uses

Catechu is used in medicine as an astringent.

Constituents

Coumarin derivatives occur in melilot although coumarin itself is not present to any extent in the living plant. It arises when the plant is crushed, or the dried material treated with water, by the action of a β-gluconidase enzyme specific to cis-o-hydroxycinnamic acid glucoside giving first the unstable hydrolytic product coumarinic acid, which then cyclizes to coumarin producing the well-known ‘new-mown hay’ odour. The trans-isomer remains unchanged and is isolated as melilotoside (see F. Bourgoud et al., Phytochem. Anal., 1994, 5, 127; P. Bradley British Herbal Compendium,

Vol. 2, 2006, p. 270). Other acids isolated from melilot include dihydro-o-coumaric acid (melilotic acid), caffeic acid and other minor acids. Various oleanene saponins, volatile compounds and flavonoids have also been reported.

The pharmacopoeial TLC identification test for melilot indicates the presence of coumarin and possibly o-coumaric acid in the genuine drug. Assay of the coumarin content, minimum 0.3%, involves absorbance measurements at 275 nm on a boiled methanolic extract of the powder.

The various traditional medical uses of the drug have yet to be firmly established by clinical trials.

History

Senna appears to have been used since the ninth or tenth century, its introduction into medicine being due to the Arabian physicians, who used both the leaves and the pods. It was formerly exported through Alexandria, from where the name of the Sudanese drug is derived.

Collection and preparation

Alexandrian senna is collected mainly in September, from both wild and cultivated plants. The branches bearing leaves and pods are dried in the sun and conveyed to Omdurman. Here the pods and large stalks are first separated by means of sieves (see ‘Senna Fruit’). That which has passed through the sieves is then ‘tossed’ in shallow trays, the leaves working to the surface and heavier stalk fragments and sand to the bottom. The leaves are then graded, partly by means of sieves and partly by hand-picking into (1) whole leaves, (2) whole leaves and half-leaves mixed, and (3) siftings. The whole leaves are those usually sold to the public, while the other grades are used for making galenicals. The drug is packed, somewhat loosely, in bales and sent by rail to Port Sudan, from where it is exported.

Tinnevelly senna is obtained from cultivated plants of Cassia angustifolia grown in South India, N.W. Pakistan and Jammu, where the plants are more luxuriant than those found wild in Arabia. It may be grown either on dry land or in wetter conditions as a successor to rice. Being a legume, it usefully adds nitrogen to the soil. Owing to the careful way in which the drug is collected and compressed into bales, few leaflets are usually broken.

Macroscopical characters

Senna leaflets bear stout petiolules. The lamina has an entire margin, an acute apex, and a more or less asymmetric base. The surfaces are pubescent. Odour, slight but characteristic; taste, mucilaginous, bitterish and unpleasant.

Typical senna leaflets are shown in Fig. 21.10. The main differences between the two varieties are given in Table 21.4.

Fig. 21.10 Senna leaflets. A, Indian senna; B, Alexandrian senna (both ×1); C, transverse section of leaflet (×80); D–H, elements of the powder (all ×200); D, leaflet fragment in transverse section; E, F, epidermal fragments in surface view; G, isolated trichomes; H, portion of fibre group with crystal sheath, c, collenchyma; cic, cicatrix; cr₁, cr₂, calcium oxalate crystals of the cluster and prismatic type respectively; f, fibre groups; l.e, lower epidermis; l.p, lower palisade layer; m, mesophyll; muc, mucilage; m.a, mucronate apex; p.m, press mark; s, stoma (paracytic type); u.e, upper epidermis; u.p, upper palisade layer; xy, xylem.

Table 21.4 Comparison of Alexandrian and Indian senna leaves.

* For full details, see Nandy and Santra, J. Ind. Pharm. Manuf., 1968, 6, 235.

† See Lemli et al., Planta Med., 1983, 49, 36.

Microscopical characters

Senna leaflets have an isobilateral structure (see Fig. 41.4). The epidermal cells have straight walls, and many contain mucilage. Both surfaces bear scattered, unicellular, non-lignified warty hairs up to 260 mu;m long (Fig. 21.10D, G). The stomata have two cells with their long axes parallel to the pore and sometimes a third or fourth subsidiary cell (Fig. 21.10E, F). The mesophyll, consisting of upper and lower palisade layers and median spongy mesophyll, contains cluster crystals about 15–20 μm in diameter. The midrib is biconvex. Below the midrib bundle is a zone of collenchyma. The midrib bundle and larger veins are almost surrounded by a zone of lignified pericyclic fibres and a sheath of parenchymatous cells containing prisms of calcium oxalate 10–20 μm long (Fig. 21.10 C).

Vein-islet numbers and stomatal indices can be used to distinguish the two species (see Table 21.4) and the BP/EP utilizes stomatal index.

Constituents

Since Tutin first isolated aloe-emodin and rhein in 1913, many other compounds based on these two have been obtained. Stoll et al. (1941) isolated two active crystalline glycosides, sennoside A and sennoside B. They both hydrolyse to give two molecules of glucose and the aglycones sennidin A and B. Sennidin A is dextrorotatory and B is its mesoform formed by intramolecular compensation (Fig. 21.12).

Fig. 21.12 Constituents of Senna.

The activity of senna was still not fully explained by the isolation of these constituents, and later work, notably by Fairbairn, Friedrich, Friedmann, Lemli and their associates demonstrated the presence of many other (some pharmacologically active) components. These include: sennosides C and D, which are the glycosides of heterodianthrones involving rhein and aloe-emodin; palmidin A (see ‘Rhubarb’); aloe-emodin dianthrone-diglycoside, rhein-anthrone- 8-glycoside, rhein-8-diglucoside, aloe-emodin-8-glucoside, aloe- emodin-anthrone-diglucoside, possibly rhein-1-glucose, and a primary glycoside having greater potency than sennosides A and B and distinguished from them by the addition of two glucose molecules. A new anthraquinone glycoside, emodin-8-O-sophoroside (a diglucoside), has been isolated in 0.0027% yield from dried Indian senna leaves (J. Kinjo et al., Phytochemistry, 1994, 37, 1685).

Two naphthalene glycosides isolated from senna leaves and pods (Lemli et al., Planta Med., 1981, 43, 11) are 6-hydroxymusizin glucoside and tinnevellin glucoside. The former is found in Alexandrian senna and the latter in Indian senna; this difference has been used as a

distinguishing feature of the commercial varieties, see Table 21.4. Senna also contains the yellow flavonol colouring matters kaempferol (3,4′,5,7-tetrahydroxyflavone), its glucoside (kaempferin) and isorhamnetin; also a sterol and its glucoside, mucilage, calcium oxalate and resin. The structures of water-soluble polysaccharides and a lignan have been reported.

Although senna is not noted for its volatile components, Tutin in his 1913 publication had observed the ‘strongly aromatic dark-coloured essential oil’. Over 80 years later W. Schulz et al. (Planta Medica, 1996, 62, 540) have again examined the volatiles of senna leaf and recorded (GC-MS) more than 200 components afforded by aqueous distillation. 122 constituents were identified including monoterpenes, phenylpropanes, fatty acids and esters, etc. Hexadecanoic acid was a significant component in addition to many of the more common constituents of volatile oils.

Formation and distribution of anthraquinone derivatives. In young senna seedlings chrysophanol is the first anthraquinone formed, then aloe-emodin appears and finally rhein; this ontogenetic sequence is in keeping with the expected biogenetic order, which involves the successive oxidation of the 3-methyl group of chrysophanol (Table 21.3). In the presence of light glycosylation follows and later the glycosides are translocated to the leaves and flowers. During fruit development the amounts of aloe-emodin glycoside and rhein glycoside fall markedly, and sennosides accumulate in the pericarp.

Lemli and Cuveele (Planta Med., 1978, 34, 311) considered that fresh leaves of Cassia senna contain anthrone glycosides only. By drying between 20 and 50°C these are enzymatically converted to dianthrone forms (sennosides). However, Zenk and coworkers (Planta Med., 1981, 41, 1) maintained that sennoside formation is not entirely an artefact arising through drying but that these compounds together with the monoanthrones, and their oxidized forms (anthraquinones), are part of a redox system of possible significance to the living cell.

The distribution of sennoside B (determined by Zenk and coworkers by immunoassay) was for a C. angustifolia plant (sample dried at 60°C): flowers 4.3%, leaves 2.8%, pericarp 2.4%, stems 0.2%, roots 0.05%. Within the flowers the anthers and filaments contained 7.2%, carpels and ovaries 5.8%, petals 5.2%, sepals 4.7% and flower stalks 3.2%.

Evaluation

It is difficult to remove all fragments of rachis, petiole and stalk from the drug, but the amount of these structures is limited by the BP to 3%. In the whole drug the percentage of these is determined by hand-picking and weighing, but with the powdered drug recourse has to be made to quantitative microscopy.

C. senna is cultivated in Russia and the leaves are harvested mechanically; this leads to unavoidable mixture with petioles and stems but, because the active constituents are similar in all parts of the plant, this does not affect the quality of the glycosidal extracts.

Lack of knowledge of the precise active principles of senna coupled with the synergistic action of various compounds hampered the development of a satisfactory chemical assay for the drug. The BP/EP determines the total senna leaf glycosides in terms of sennoside B (not less than 2.5%). This involves extraction of the glycosides and free anthraquinones from the leaves, removal of the free aglycones and hydrolysis and oxidation of the remaining sennosides and other glycosides to give rhein and some aloe-emodin, which are then determined spectrophotometrically. Chromatographic tests for the leaf are given in the BP and EP.

The leaves are officially required to give an acid-insoluble ash of not more than 2.5%.

Allied drugs

Bombay, Mecca and Arabian Sennas are obtained from wild plants of C. angustifolia grown in Arabia. Some of the leaflets are shipped to Port Sudan and are graded like the Alexandrian drug, while some are sent to Bombay and frequently arrive in England with shipments of the Tinnevelly.

The leaflets resemble those of Tinnevelly senna but are somewhat more elongated and narrower, and of a brownish or brownish-green colour. Levin (1929) states that they may be distinguished microscopically from other sennas by their vein islet number.

Dog senna, a variety formerly much esteemed and still used in France, is derived from Cassia obovata. The plant is indigenous to Upper Egypt, but was cultivated in Italy in the sixteenth century. The leaves are obovate and quite different in appearance from the official leaflets. When in powder they may be distinguished by the papillose cells of the lower epidermis. Maurin found them to contain 1.0–1.15% of anthraquinone derivatives.

Palthé senna, derived from Cassia auriculata, has been found in Indian senna. It may be distinguished by the long hairs, the crimson colour given when boiled with chloral hydrate solution or treated with 80% sulphuric acid and the absence of anthraquinone derivatives. The leaves of other parts of the plant are widely used in Ayurvedic medicine for rheumatism and diabetes. The antioxidant activity of the flowers has been recently demonstrated (L. Pari and M. Latha, Pharm. Biol., 2002, 40, 512; A. Kumaran and R. J. Karunakaran, Fitoterapia, 2007, 78, 46).

The leaflets of other species of Cassia have also been imported, but may be distinguished from the genuine drug by the characters given above.

For Nigeria, the leaves of the local Cassia podocarpa have been suggested as a substitute for the official senna; bioassays have given an equivalent activity (A. A. Elujoba and G. O. Iweibo, Planta Med., 1988, 54, 372).

C. alata produces anthraquinone derivatives and has been used traditionally in Thailand as a laxative. Root cultures have been studied for their anthraquinone-producing properties (N. Chatsiriwej et al., Pharm. Biol., 2006, 44, 416).

Substitute

Argel leaves, which are derived from Solenostemma arghel (Asclepiadaceae), were at one time regularly mixed in a definite proportion with Alexandrian senna. The plant occurs in the Sudan, but the leaves are now seldom seen in commerce. If used to adulterate senna powder, it may be distinguished by the two- or three-celled hairs, each of which is surrounded by about five subsidiary cells.

Collection

The pods are collected with the leaves and dried as described above. After separation from the leaves they are hand-picked into various qualities, the finer being sold in cartons and the inferior ones used for making galenicals.

Characters

The characteristic sizes and shapes of the two varieties are shown in Fig. 21.11. The Tinnevelly pods are longer and narrower than the Alexandrian and the brown area of pericarp surrounding the seeds is greater. The remains of the style are distinct in the Tinnevelly but not in the Alexandrian.

Fig. 21.11 Senna fruits. A, Tinnevelly fruit; B, Alexandrian fruit; C, Alexandrian pod opened to show seeds (all ×1); D, seed of Alexandrian fruit; E, seed of Tinnevelly fruit; F, transverse section of seed; G, isolated embryo with one cotyledon removed (all ×4); H, stem with Tinnevelly fruit attached (×1); I, transverse section of pericarp (×90;) J, transverse section of seed coat; K, fragments of epidermis with stomata; L, fragment of epidermis with trichome; M, fibrous layers from endocarp in surface view (all ×200); a, brown areas of pericarp covering seeds; c, cotyledons; e, endosperm; e.f, fibrous endocarp; ep, epicarp; f, funiculus; m, mesocarp; p, plumule; pl, placenta; p.l, parenchymatous layers of testa; p.m, press marks from other pods; r, radicle; s, seed; st, stalk; s.p, (J) subepidermal palisade; s.p, (A), stylar point; s.r, spathate ridge; tr, trichome; v.b, vascular bundle partially enclosed by fibres.

After soaking in water the pods are readily opened and about six wedge-shaped seeds are disclosed, each attached to the dorsal surface of the pod by a thin funicle (Fig. 21.11C). Under a lens the testas ofthe Tinnevelly show a general reticulation and wavy, transverse ridges, while the Alexandrian show a general reticulation only (Fig. 21.11D, E). The pericarp of the pod bears unicellular hairs and stomata of a type similar to those found on senna leaves; portions of the fibrous layer of the endocarp are very evident in the powder (Fig. 21.11K, L, M).

Constituents

The active constituents of the pods are located in the pericarp; they are similar to those of the leaves, together with sennoside A, which constitutes about 15% of the sennoside mixture. The seeds contain very little sennoside but Zenk’s group reported the cotyledons of 3-day-old seedlings to contain amounts equivalent to those in the leaves. Sennoside content varies from about 1.2 to 2.5% in the Tinnevelly (BP/EP 2.2%) and from about 2.5 to 4.5% in the Alexandrian (BP/EP 3.4%). C. Terreaux et al. (Planta Medica, 2002, 68, 349) have reported the isolation of kaempferol and tinnevellin 8-glucoside from an extract of the Tinnevelly pods together with two new carboxylated benzophenone glucosides. Preparations of the powdered pericarp, e.g. Senna Tablets BP, standardized in terms of sennoside B, are now commonly prescribed.

Uses

The use of laxatives is increasing and senna constitutes a useful purgative for either habitual constipation or occasional use. It lacks the astringent after-effect of rhubarb. Despite the availability of a number of synthetics, sennoside preparations remain among the most important pharmaceutical laxatives.

History

Cascara is a drug of comparatively recent introduction into modern medicine. According to tradition, a cascara, probably R. californica, was known to early Mexican and Spanish priests of California; Rhamnus purshianus, however, was not described until 1805 and its bark was not introduced into medicine until 1877.

The common, European buckthorn was well known to the Anglo- Saxons; its berries were official in the London Pharmacopoeia of 1650.

Collection and storage

The bark is collected from mid-April to the end of August, when it separates readily from the wood. Longitudinal incisions about 5–10 cm apart are first made in the trunk and the bark removed. The tree is then usually felled and the branch bark separated. The pieces are dried in the shade with the cork uppermost. Such material is referred to as ‘natural’ cascara but commercial supplies are now comminuted to give small even fragments known as ‘evenized’, ‘processed’ or ‘compact’ cascara. During preparation and storage the bark must be protected from rain and damp, or partial extraction of the constituents may occur or the bark may become mouldy. That the bark must be kept for at least 1 year before use is no longer a BP requirement but the bark appears to increase in medicinal value and price until it is about 4 years old. Many companies prefer to use bark which has been stored for considerably more than 1 year. To reduce freight and handling charges on the bark, large quantities of the extract are now imported directly.

Macroscopical characters

The bark occurs in quills, or channelled or nearly flat pieces. All of these forms may attain 20 cm in length and are 1–4 mm thick, the thinner bark being most esteemed. The flat strips from the trunk are usually much wider (up to 10 cm) than the quills or channelled pieces (about 5–20 mm) obtained from the branches.

Cascara (Fig. 21.13A) bears a somewhat patchy, silvery-grey coat of lichens. Pieces bearing moss are also quite common. Between the patches of lichen may be seen a smooth, dark purplish-brown cork marked with lighter-coloured, transversely elongated lenticels. On scraping the cork, no bright purple inner cork is disclosed (distinction from R. alnus). The inner surface is dull purplish-brown to black, striated longitudinally and somewhat corrugated transversely. The fracture is short and granular in the outer part, but somewhat fibrous in the phloem. In the yellowish-brown cortex and phloem lighter groups of sclerenchymatous cells and phloem fibres may be seen with a lens. They may be made more distinct by staining with phloroglucinol and hydrochloric acid. The medullary rays, which tend to curve together in groups, are well seen in sections mounted in potash. Odour, slight but characteristic; taste bitter.

Fig. 21.13 Cascara bark. A, single quill (×0.66); B, general diagram of transverse section of bark (×20); C, transverse section of outer tissues; D, ditto of phloem (both × 200); E, cork cells in surface view; F, fragment of phloem from powder (both × 250); c, collenchyma; ck, cork; c.p, cortical parenchyma; I, lenticel; li, lichen patch; I.f, longitudinal furrows; m, moss; m.r, medullary ray; m.s, mussel scale; ox₁, ox₂, prismatic and cluster crystals of calcium oxalate respectively; p.f, pericyclic fibres; ph.f, phloem fibres; ph.p, phloem parenchyma; s, sclereids; s.p, sieve plate; s.t, sieve tube; t, scar of twig.

Microscopical characters

A transverse section of cascara bark (Fig. 21.13B–D) shows a partial coat of whitish lichen, some 10–15 layers of flattened cork cells with reddish-brown contents and a cortex composed of collenchyma, parenchyma and groups of sclereids. The collenchymatous cells show thickened pitted walls and contain chloroplasts filled with starch. Some of the parenchymatous cells also contain chloroplasts and starch; many of them contain a yellow substance coloured violet by alkalis and rosette crystals of calcium oxalate usually 6–10 μm diameter, but occasionally up to 45 μm diameter. The parenchymatous cells abutting on the groups of sclereids contain prisms of calcium oxalate. The sclereids are irregular or ovoid in shape, are variable in size, and have thick lignified walls sometimes showing stratification and traversed by funnel-shaped pits. A pericycle is not clearly delimited, but the zone immediately outside the phloem in which sclereids and occasional fibres occur is regarded as representing this region. The phloem is composed of zones of tangentially elongated groups of phloem fibres, enclosed in a sheath of parenchymatous cells containing prisms of calcium oxalate which alternate with sieve tubes and phloem parenchyma (Fig. 21.13F). The individual fibres are yellow in colour, are 8–15 μm in diameter, and have thick lignified walls showing stratification and pit canals. The sieve tubes show sieve plates, each with several sieve fields, on the radial walls. The sieve plates are usually covered with a deposit of callus and can be identified after staining with alkaline solution of corallin. The phloem parenchyma resembles that of the cortex, containing plastids, starch, material coloured violet by alkali, and rosettes of calcium oxalate. The medullary rays are 1–5 cells wide and 15–25 cells deep. The medullary ray cells are parenchymatous, somewhat radially elongated and with similar contents to those of the parenchyma; their content of material stained violet by alkali is often high. Fragments of moss leaves and liverworts are usually found in the powder.

Constituents

It has long been recognized that cascara bark stored for at least 1 year gave galenicals which were better tolerated but as effective as those prepared from more recently collected bark. This is presumably due to hydrolysis or other changes during storage. It was also found at an early date that the very bitter taste of cascara is reduced by treating extracts with alkalis, alkaline earths or magnesium oxide. Proprietary extracts of this type became very popular and pharmacopoeias followed the same idea to produce such preparations.

Cascara contains about 6–9% anthracene derivatives which are present both as normal O-glycosides and as C-glycosides. The following groups of constituents are now manifest.

1 Four primary glycosides or cascarosides A, B, C and D; they contain both O- and C-glycosidic linkages. Their structures were elucidated in 1974 by Wagner et al. as the C-10 isomers of the 8-O-β-D-glucopyranosides of aloin and chrysophanol. A. Griffini et al. (Planta Med., 1992, 58, Suppl. 1, A593) described the isolation of the pure cascarosides by silica-gel chromatography and HPLC. The complete assignments of ¹H- and ¹³C-NMR signals for these cascarosides were recorded by Manitto et al. (J. Chem. Soc. Perk. Trans I, 1993, 1577) and the same group (J. Nat. Prod., 1995, 38, 419) have now isolated two analogous glycosides (cascarosides E and F) derived from emodin (Table 21.3).

The primary glycosides are more active than the aloins whereas the free anthraquinones and dimers have little purgative activity. The cascarosides have a sweet and more pleasant taste than the aloins. The BP/EP requires the bark to contain not less than 8.0% of hydroxyanthracene glycosides of which not less than 60% consists of cascarosides, calculated as cascaroside A. A two-point spectro-photometric assay is employed with absorbance measurements at 515 nm and 440 nm.

Experiments by Betts and Fairbairn in 1964, although based on a single fresh plant, suggested that free anthraquinones are formed by the leaves and that they are stored in the bark mainly as C-glycosides, the older bark containing the most C-glycosides. Rhamnus purshianus cell suspension cultures will produce anthracene derivatives in which the accumulation of these compounds, particularly emodin, is significantly raised by a 12 h light/dark cycle; continuous illumination of the cultures suppresses anthraquinone formation.

Substitutes

Several species of Rhamnus have a similar geographical distribution to that of R. purshianus. These include R. alnifolia, which is too rare to be a likely substitute; R. crocea, whose bark bears little resemblance to the official drug, and R. californica Esch. The latter is so closely related to R. purshianus that some botanists do not divide them into separate species. The plant appears to have a much more southerly distribution than the typical R. purshianus and is therefore unlikely to occur in bark of Canadian origin. It has a more uniform coat of lichens and wider medullary rays than the official species, but resembles the latter in having sclerenchymatous cells. The bark of R. fallax has been recorded as a cascara substitute. European frangula bark, distinguished by the BP/EP TLC test, is described below.

Uses

Cascara is a purgative resembling senna in its action. It is mainly used in the form of liquid extract or elixir or as tablets prepared from a dry extract. It is also used in veterinary work.

Allied drugs

The common buckthorn, Rhamnus cathartica, has a glossy reddish-or greenish-brown cork and does not possess sclereids. It contains frangula-emodin and a glycoside, rhamnicoside, which yields on hydrolysis rhamnicogenol (an anthraquinone derivative), glucose and xylose. Rauwald and Just (Planta Med., 1981, 42, 244) reported the isolation of the anthraquinone glycoside alaternin; 1,2,6,8- tetrahydroxy-3-methyl-anthraquinone; physcion; chrysophanol; and frangula-emodin. The bark also contains a number of blue-fluorescent substances which in the chromatograms produced by the BP/EP tests of identity for Cascara and Frangula serve to distinguish this adulterant. The fluorescent substances have recently been identified as naphtholide glycosides of the sorigenin type, as below.

The bark of R. carniolica has a dull reddish cork and differs from frangula bark in that it possesses sclerenchymatous cells and has wider medullary rays. In recent years the barks of a number of Turkish species of Rhamnus have been systematically examined for their anthraquinone and flavonoid contents (see M. Koskun, Int. J. Pharmacognosy, 1992, 30, 151 and references cited therein).

Species and commercial grades

The genus Rheum comprises about 50 species, which may be classified into two sections, the first including R. palmatum and R. officinale, and the second R. rhaponticum, R. undulatum and R. emodi. A systematic study is made unusually difficult by geography and by the tendency of cultivated plants to form hybrids such as R. palmatum × R. undulatum and R. palmatum × R. emodi. The exact morphological and chemical characters of such hybrid rhizomes appear not to have been described. Formerly most of the drug was derived from R. palmatum L. var. tanguticum Maximowicz and R. officinale H. Br. and was traditionally known in commerce as Shensi, Canton and high-dried rhubarb. R. palmatum and R. palmatum var. tanguticum now appear to be the chief sources. The best grade of the present-day drug corresponds to that formerly known as Shensi rhubarb. Another present-day grade is similar to the old Canton. In addition, some inferior drug is exported, much of which fails to give the pink fracture characteristic of good-quality rhubarb.

In practice the grading system is more complex than the above might imply, and currently about a dozen grades of rhubarb are recognized by merchants. The grades commonly listed are: ‘flat’, ‘common round’, ‘small round’, ‘extra small round’, ‘sticks’, ‘third grade’ and lower qualities. The flat and round are further categorized on a percentage basis (e.g. ‘flat 90%’ or ‘common round 80%’), depending on the pinkness and quality of the fracture. However, not all of these grades are necessarily available at any one time. Currently (2000) it is almost impossible to obtain rhubarb from China which meets BP/EP requirements for hydroxyanthraquinone derivatives. Demand for the better grades (CR & Flat 80 & 90%) is now almost exclusively for the beverage industry.

History

Chinese rhubarb has a long history. It is mentioned in a herbal of about 2700 BC and subsequently formed an important article of commerce on the Chinese trade routes to Europe. Today it still holds a place in medicine. The first international symposium on the drug was held in Chengde, China in 1990 under the title ‘Rhubarb 90’.

Collection and preparation

Provided that the older accounts are still substantially correct, the rhizomes are grown at a high altitude (over 3000 m) dug up in autumn or spring when about 6–10 years old, decorticated and dried. The decorticated rhizomes are when whole roughly cylindrical (‘rounds’) or if cut longitudinally are in planoconvex pieces (‘flats’). Pieces used often to show a hole indicating that they had been threaded on cords for drying.

The drug is exported from Shanghai to Tientsin, often via Hong Kong. The better qualities are packed in tin-lined wooden cases containing either 280 lb or 50 kg, and inferior quality in hessian bags.

Botanical characters of rhizome

The rhizomes of R. palmatum and R. officinale are similar in structure except for the size and distribution of the abnormal vascular bundles, ‘star spots’, of the pith. Transverse sections of both, after peeling, show phloem on the outside, cambium, radiate wood and a pith with ‘star sports’ (Fig. 21.14A, B). In R. palmatum the latter are relatively small (about 2.5 mm) and most of them are arranged in a continuous ring; in R. officinale the ‘star spots’ are larger (about 4 mm) and are irregularly scattered.

Fig. 21.14 Chinese rhubarb. A, common round (×0.5); B, star spot in transverse section (×20); C–E, fragments of the powder (×200); C, portions of reticulate vessels; D, calcium oxalate crystals; E, starch; c, cambium; cr, crystals; f, facets produced by peeling; m.r, medullary ray; ph, phloem; st, star spot; v, vessel; x.p, xylem parenchyma.

Macroscopical characters

Despite the large number of commercial grades, it is convenient to describe the various rhubarb types under three headings.

Microscopy of powder

Powdered rhubarb (Fig. 21.14) is easily identified. It shows abundant calcium oxalate rosettes up to 200 μm in diameter; simple two to five compound starch grains; reticulate vessels and other wood elements which give no reaction for lignin. The yellow contents of the medullary ray cells (anthraquinone derivatives) become reddish-pink with ammonia solution and deep red with caustic alkalis.

Constituents

As with other anthraquinone-containing drugs, the chemical complexity of rhubarb was not fully appreciated by the earlier research workers. Free anthraquinones were the first substances to be isolated: chrysophanol, aloe-emodin, rhein, emodin and emodin monomethylether or physcion (1844–1905). Glycosides of some of the above were also separated. These substances did not account satisfactorily for the action of the drug, and modern methods of investigation have established the presence of the following types of anthraquinones in rhubarb.

In addition to the above purgative compounds, rhubarb contains astringent compounds such as glucogallin, free gallic acid, (–)-epicatechin gallate and catechin. Other derivatives of gallic acid include glycerol gallate, gallic acid glucoside gallates and isolindleyin (a methyl p-hydroxyphenylpropionate derivative of a glycogallate). A new class of gallototannins has a sucrose core and chromone glucosides have also been identified (Y. Kashiwada et al., Phytochemistry, 1988, 27, 1469; 1990, 29, 1007).

Rhubarb also contains starch and calcium oxalate. The total ash is very variable, as the amount of calcium oxalate varies from about 5 to 40%. The acid-insoluble ash should not exceed 1%. The BP assay for anthraquinone derivatives is a spectrophotometric method and replaces the former standard for alcohol-soluble extractive.

Ontogenetic production of anthraquinone derivatives

As the drug is collected in autumn, variations in constituents arising from seasonable changes should present no problem. Nevertheless, considerable research has been devoted to this aspect over many years. Work by Lemli and colleagues (1982) indicated that oxidized compounds, the anthraquinones, are the major components of the anthracene mixture in the summer months and the reduced forms, the anthrones, in winter. The conversions occur within a time lapse of about 3 weeks, and just before each, the anthrone diglycoside content increases markedly. Experiments showed that the anthraquinone → anthrone conversion could be artificially induced by decreasing the ambient temperature. Earlier reports by Schmid (1951) suggested that the age of the rhizome also affected the ratio of reduced:oxidized glycosides. Chinese workers have also addressed the problem (Chem. Abs., 1992, 117, 66652; 66653).

Constituents of rhapontic rhubarb

Rhapontic rhubarb contains a glycoside, rhaponticin, which is a stilbene (diphenylethylene) derivative of the formula

This substance and desoxyrhaponticin (glycoside of 3,5-dihydroxy-4′-methoxystilbene) account for the difference in fluorescence between official and rhapontic rhubarbs. Rhapontic rhubarb does contain anthraquinone derivatives, although these differ from those in the official drug. One is the glucoside glucochrysaron (see Table 21.3).

Chemical tests

Other rhubarbs

Uses

Rhubarb is used as a bitter stomachic and in the treatment of diarrhoea, purgation being followed by an astringent effect. The drug is suitable as an occasional aperient but not for the treatment of chronic constipation.

Plants

Of about 180 known species of Aloe, the drug is mainly obtained from the following: Cape variety from Aloe ferox and its hybrids; Curaçao variety from Aloe barbadensis; Socotrine and Zanzibar varieties from Aloe perryi. The genus Aloe includes herbs, shrubs and trees, bearing spikes of white, yellow or red flowers. Aloe ferox is an example of the arborescent type and A. barbadensis of the herbaceous type. Aloe leaves are fleshy, are strongly cuticularized and are usually prickly at the margins.

It has been suggested that if natural stocks of A. ferox became exhausted then A. classenii and A. turkanensis would be preferable for cultivation because chemical races would not be a problem and their production of sideshoots would make vegetative propagation easier. However, some problems have arisen concerning the commerce in the African aloes because the Washington Conference of the Convention on International Trade in Endangered Species (CITES) placed all species of Aloe, with the exception of A. vera (a cultivar of A. barbadensis), on the protected list.

Leaf structure

Transverse sections of an Aloe leaf usually show the following zones: (1) a strongly cuticularized epidermis with numerous stomata on both surfaces; (2) a region of parenchyma containing chlorophyll, starch and occasional bundles of needles of calcium oxalate; (3) a central region which frequently occupies about three-fifths of the diameter of the leaf, consisting of large, mucilage-containing parenchymatous cells; (4) a double row of vascular bundles which lie at the junction of the two previous zones and have a well-marked pericycle and endodermis. The aloetic juice from which the drug is prepared is contained in the large, pericyclic cells and sometimes in the adjacent parenchyma. When the leaves are cut, the aloetic juice flows out. No pressure should be applied or the aloes will be contaminated with mucilage. The mucilage, contained in zone 3 as above is used in the cosmetic and herbal industries in ‘aloe vera’ preparations (see Chapter 19).

History

According to legend, Socotrine aloes was known to the Greeks as early as the fourth century BC; the Greek colonists were sent to the island by Alexander the Great solely to preserve and cultivate the aloe plant. The drug was apparently known in England in the tenth century, and from the seventeenth century records of the East India Company it would appear that they frequently purchased the whole stock of aloes of the ‘King of Socotra’. Socotrine and Zanzibar aloe were for many years the only official aloes, but they have now been replaced by the Cape and Curaçao varieties. Cape aloes was first exported about 1780 and became official in Britain in 1932. Barbados aloes was produced from about 1650 and lapsed about the beginning of the present century. The production of Curaçao (also called Barbados) aloes was started by the Dutch in the Islands of Curaçao, Aruba and Bonaire about 1817; recently aloes of similar type has been exported from nearby Venezuela.

Preparation and characters of Cape aloes

Cape aloes is prepared from wild plants of A. ferox and its hybrids. The leaves are cut transversely near the base and about 200 of them are arranged round a shallow hole in the ground, which is lined with plastic sheeting or more traditionally a piece of canvas or a goatskin. The leaves are arranged so that the cut ends overlap and drain freely into the canvas. After about 6 h all the juice has been collected and it is transferred to a drum or paraffin tin in which it is boiled for about 4 h on an open fire. The product is poured while hot into tins, each holding 25 kg, where it solidifies. For export the tins are placed in cases holding either two, four or eight tins.

The drug occurs in dark-brown or greenish-brown, glassy masses. Thin fragments have a deep olive colour and are semitransparent. The powder is greenish-yellow, and when pieces of the drug have rubbed against one another, patches of powder are found on the surface. The drug has a very characteristic, sour odour (the so-called rhubarb or apple-tart odour), which is particularly noticeable if one breathes on the drug before smelling. Taste, nauseous and bitter. The powder when examined under the microscope in lactophenol is usually amorphous.

Preparation and characters of Barbados (Curaçao) aloes

Curaçao aloes is produced from cultivated plants of A. barbadensis. The cut leaves are stacked in V-shaped troughs arranged on a slope so that the juice flows from a hole at one end of the trough into a collecting vessel. When sufficient juice has been collected, it is evaporated in a copper vessel. The temperature used is generally lower than in the case of Cape aloes and the product is, therefore, usually opaque, although some which is semi-transparent may be produced and is known in commerce as ‘Capey Barbados’. Originally Barbados and Curaçao aloes were packed in gourds, now seen only in museums. The present-day drug is exported in cases each holding about 58.5 kg.

Typical Barbados aloes varies in colour from yellowish-brown to chocolate-brown, but poorer qualities that have been overheated may be almost black. The drug is opaque and breaks with a waxy fracture. The semi-transparent ‘Capey Barbados’ becomes more opaque on keeping. Curaçao has a nauseous and bitter taste and a characteristic odour recalling iodoform. Mounted in lactophenol, it shows small acicular crystals.

Substitutes and adulterants

Socotrine and Zanzibar aloes are now rare in the British market, and Natal aloes from A. candelabrum is no longer imported. Socotrine is yellowish-brown to blackish-brown, opaque and breaks with a porous fracture. Zanzibar is similar but has a waxy fracture and may be packed with leaves or skins (so-called ‘monkey-skin aloes’). All may be distinguished from official aloes by chemical tests.

Chemical tests

A chromatographic test is included in the BP/EP together with assays for hydroxyanthracene derivatives. Of the latter Barbados aloes should contain not less than 28% and Cape aloes not less than 18% calculated as barbaloin.

Constituents

Aloes contain C-glycosides and resins. The crystalline glycosides known as ‘aloin’ were first prepared by T. and H. Smith of Edinburgh, UK, from Barbados aloes in 1851; Aloin (BP, 1988) contains not less than 70% anhydrous barbaloin. The main crystalline glycoside, barbaloin, is found in all the commercial varieties (Leger, 1907). Leger showed that on heating to about 160°C barbaloin is partly converted into amorphous beta;-barbaloin. This substance is said to be absent from the Barbados variety, but present to the extent of about 8% in the Cape.

Barbaloin is a C-glycoside—a 10-glucopyranosyl derivative of aloe-emodin-anthrone. Unlike O-glycosides, it is not hydrolysed by heating with dilute acids or alkalis. It can, however, be decomposed by oxidative hydrolysis, with reagents such as ferric chloride, when it yields glucose, aloe-emodin anthrone and a little aloe-emodin. It will be seen from the formula of barbaloin that stereoisomerism is possible at C-10; in 1979 both isomers were obtained by HPLC of a methanolic extract of Aloe ferox and in 1980 Auterhoff et al. separated commercial aloin into its stereoisomers. The absolute configuration of the two aloins was independently elucidated by Rauwald et al. (Angew. Chem., Int. Ed. Engl., 1989, 28, 1528) and Manitto et al. (J. Chem. Soc., Perk. Trans. I, 1990, 1297); aloin A is (10S)-barbaloin and aloin B the (10R)-epimer (Fig. 21.15). The two are interconvertible via the corresponding anthranol form. All varieties of aloes give a strong greenish fluorescence with borax, a characteristic of anthranols, which are readily formed from anthrones by isomeric change. This has long been used as a general test for aloes.

Fig. 21.15 Constituents of aloes

Small quantities of aloe-emodin are sometimes present in aloes, and Cape aloes also contains aloinosides A and B, which are O-glycosides of barbaloin; aloinoside B has rhamnose attached via an oxymethyl group at C-3. In A. barbadensis free and esterified 7-hydroxyaloins A and B are characteristic 10-C-glucosyl-anthrones. These compounds are responsible for the violet-purple colours given in various specific tests for Barbados aloes (see H. W. Rauwald et al., Planta Med., 1991, 57, Suppl. 2, A129).

The resin of aloes, reputed to have a purgative action, has been periodically investigated from the end of the nineteenth century onwards. In South African spp. (e.g. A. ferox) aloesin (now often referred to asaloeresin B) was identified in 1970 by Haynes et al., and was the first C-glucosyl-chromone to be described. Other 5-methylchromones isolated from Cape aloes include aloeresin A and C which are p-coumaroyl derivatives linked via a hydroxyl of the glucose. Two non-glucosylated 5-methylchromones present in smaller amounts than the aloesins were reported in 1997. A glycosidic 6-phenylpyran-2-one derivative (aloenin A) was isolated and characterized from A. arborescens leaves in 1974 by Japanese workers. Aloenin B has now been obtained from Kenya aloes (see formulae). (For research on these and related constituents see G. Speranza et al., Phytochemistry, 1993, 33, 175; J. Nat. Prod., 1992, 55, 723; 1993, 56, 1089; 1997, 60, 692. Two aloesol derivatives (Fig. 21.14) have been isolated: 8-C-β-D-glucopyranosyl-7-O-methyl-(R)-aloesol (L. Duri et al., Fitoterapia, 2004, 75, 520) from a commercial sample (Kenya) and the 10S diastereoisomer from A. vera (N. Okamura et al., Phytochemistry, 1996, 43, 495).

Three new naphtho[2,3-c]furan derivatives have recently been isolated from a commercial sample of Cape aloes (J. Koyama et al., Phytochemistry, 1994, 37, 1147).

As with other anthraquinone-producing plants, in Aloe species the content of anthraquinones is subject to seasonal variation, and these compounds are implicated in the active metabolism of the plant. McCarthy and coworkers in South Africa have shown that the anthraquinone derivatives are confined to the leaf juices and that aloin reaches a maximum concentration in the dried leaf juices of A. ferox and A. marlothi in the summer (24.1% in November) and is lowest in winter (14.8% in July).

Uses

Aloes is employed as purgative. It is seldom prescribed alone, and its activity is increased when it is administered with small quantities of soap or alkaline salts, while carminatives moderate its tendency to cause griping. It is an ingredient of Compound Benzoin Tincture (Friars’ Balsam).

There appears to be little variation of the major constituents of the leaf exudate of A. ferox depending on geographical location of the plant but selection of high-yielding strains giving a high production of aloin (25%) is recommended for commercial cultivation (B.-E. van Wyk et al., Planta Medica, 1995, 61, 250).

‘Aloe vera’ products See Chapter 20.

History

The plant was known in ancient Greece for its medicinal attributes and since the Middle Ages has been used for its anti- inflammatory and healing properties. It also became highly regarded for the treatment of mental illness. The generic name derives from the Greek hyper—above, and icon (eikon)—picture, referring to the ancient practice of hanging the plant above religious pictures to ward off evil spirits. The common name St John’s wort is attributed to the fact, among others, that it comes into flower around St John’s Day (June 24th).

The drug is now included in the BP/EP, a number of European pharmacopoeias, the British Herbal Pharmacopoeia, the American Herbal Pharmacopoeia, and as monographs for the German Commission E and ESCOP.

Collection

Collection is from wild and cultivated plants and increased demand has meant that farmers in the US and Australia who battled to eradicate it as a weed now harvest it as a viable crop. Care should be taken during collecting as contact photosensitivity has been reported. Drying at 70° for 10 hours is recommended.

Macroscopy

The drug consists of green leaf fragments and stems, unopened buds and yellow flowers. Oil glands are visible in the leaves as transparent areas, hence the specific name perforatum, and as small black dots on the lower surface. The opposite, sessile leaves are 1.5–4.0 cm in length, elliptical to ovate in outline, glabrous with an entire margin. Pieces of hollow stem are cylindrical with two faint ribs on either side.

The odour is distinct and the taste slightly sweet and astringent.

Microscopy

The upper epidermal cells of the leaf are sinuous in outline with beaded anticlinal walls; the lower epidermis possesses anomocytic and paracytic stomata. The mesophyll has large hypericin-containing oil glands, some with red contents, and these are also found in the petals and sepals. Pollen grains are ellipsoidal, 20–25 μm in diameter, with three pores and a smooth exine. Trichomes and calcium oxalate are absent.

In an innovative study, Rapisarda et al. (Pharm. Biol., 2003, 41, 1) have used scanning electron microscopy and image analysis involving size and shape parameters of leaf epidermal cells to provide a quantitative morphological analysis of the three Italian Hypericum spp.—H. perforatum L., H. hircinum L. and H. perfoliatum. The markers obtained provided key factors for the identification and selection of these species and their hybrids.

Constituents

Hypericum contains a variety of constituents with biological activity.

Anthraquinones. Principally hypericin and pseudohypericin; also iso-hypericin and emodin-anthrone. The BP/EP requires not less than 0.08% of total hypericins expressed as hypericin calculated with reference to the dried drug. The extracted hypericins are assayed by absorption measurement at 590 nm.

Prenylated phloroglucinol derivatives. Hyperforin (2.0–4.5%), adhyperforin and furohyperforin (L. Verotta et al., J. Nat. Prod., 1999, 62, 770), the latter at concentrations of about five per cent of the hyperforin content. These phloroglucinols constitute the principal components of the lipophilic extract of the plant and are considered to be the most important active constituents regarding antibiotic and antidepressant properties. Unfortunately, they are very prone to oxidative transformations and a number of such degradation products have been identified, see L. Verotta et al., J. Nat. Prod., 2000, 63, 412; V. Vajs et al., Fitoterapia, 2003, 74, 439. For an article, with many references, on the wide-ranging aspects of hyperforin, see L. Beerhues, Phytochemistry, 2006, 67, 2201.

The involvement of branched-chain amino acids in the biosynthesis of hyperforin and adhyperforin has been demonstrated with shoot cultures of H. perforatum: L-[U-¹³C₅] valine and L-[U-¹³C₆] isoleucine, when fed to the shoots, were incorporated respectively into the side-chains of hyperforin and adhyperforin. Production of the former was not increased by the administration of unlabelled L-valine, whereas the latter was enhanced by the feeding of the unlabelled L-isoleucine (K. Karppinen et al., Phytochemistry, 2007, 68, 1038). Two phloroglucinols, hyperfirin and adhyperfirin, previously reported to be precursors of hyperforin and adhyperforin, respectively, have now been detected in the plant (E. C. Tatsis et al., Phytochemistry, 2007, 68, 383).

Flavonoids. These include flavonols such as kaempferol, luteolin and quercetin, the flavanol glycosides quercitrin, isoquercitrin and hyperoside. The biflavonoid amentoflavone (Fig. 21.18) is confined principally to the flowers (A. Umek et al., Planta Medica, 1999, 65, 388).

Selected formulae for the above are shown in Figs 21.16 and 21.18.

Fig. 21.16 Hypericins and phloroglucinols of hypericum.

Volatile oil. Up to 0.35% consisting principally of saturated hydrocarbons including alkanes and alkanols in the range C₁₆–C₂₉.

Other constituents. Many other components of hypericum have been reported including various plant acids (caffeic, chlorogenic, etc.), amino acids, vitamin C, tannins and carotenoids.

Many reports have appeared concerning the distribution of the above constituents in different organs of the plant and generally on a weight for weight basis it is the flowers, particularly the petals, that possess the highest concentrations. According to an Australian report (I. A. Southwell et al., Phytochemistry, 1991, 30, 475) it is the narrow-leaved varieties, both in Europe and Australia, that possess a relatively high proportion of oil glands and give a higher yield of hypericin compared with the broad-leaved forms. Hypericin concentrations determined on twelve samples of herb collected throughout Oregon varied widely (0.01–0.38%) (G. H. Constantine and J. Karchesy, Pharm. Biol., 1998, 36, 365). B. Buter et al. (Planta Medica, 1998, 64, 431) have suggested that a key factor for successful future field production will rest in the selection of genetically superior strains giving increased secondary metabolite production, together with improvements in agrotechnological methods. In this connection R. J. Percifield et al. (Planta Medica, 2007, 73, 1525), studying 50 Hypericum accessions, have demonstrated the value of amplified fragment-length polymorphism analysis for the characterization of closely related samples.

Cell culture of Hypericum spp. and their chemotypes has proved extremely variable in naphthadianthrone yields with pseudohypericin production exceeding that of hypericin (T. Kartnig et al., Planta Medica, 1996, 62, 51). Flavonoids, completely different to those of the intact plant and including the new compound 6-C-prenylluteolin, have been identified in callus cultures of H. perforatum (A. P. C. Dias et al., Phytochemistry, 1998, 48, 1165).

Other Hypericum spp

The genus contains some 400 spp.; most of the more common ones have lower or nil hypericin contents and are often distinguishable in the dried condition by the nature of the ridges on the stem. H. maculatum (Imperate St John’s wort) is similar in constituents to H. perforatum but contains less; it may be distinguished by the slightly quadrangular stem and larger leaves. H. hirsutum, H. tetrapterum and H. montana are other common European species.

The essential oils of two Turkish species (H. hyssopifolium and H. lysimachioides) are rich in sesquiterpene hydrocarbons, but unlike some other species investigated, poor in monoterpene hydrocarbons. Caryophyllene oxide is a major component. Both oils possess antimicrobial activities (Z. Toker et al., Fitoterapia, 2006, 77, 57). Eight species from S. Brazil showed no detectable amounts of hypericin or pseudohypericin (A. Ferraz et al., Pharm. Biol., 2002, 40, 294). H. chinense finds use in Japanese folk medicine for the treatment of female disorders. It contains acyl phloroglucinols and spirolactones; six new xanthones have been reported (N. Tanaka and Y. Takaishi, Chem. Pharm. Bull., 2007, 55, 19).

Action and uses

An explosion in the popularity of St John’s wort related to its unregulated availability for the treatment of mild to moderate depression. In the USA, for the first eight months of 1999, it ranked second to ginkgo as the best-selling product of the herbal mainstream market, with retail sales valued at over 78 million (M. Blumenthal, HerbalGram, 1999, 47, 64). In Germany, it represented 25% of all antidepressant prescriptions. It was described as ‘nature’s Prozac’, without the disadvantageous side-effects of the latter. However, a cautionary warning was struck by two reports (S. Piscitelli et al., Lancet, 2000, 355, 547; F. Ruschitzka et al., Lancet, 548). In the first, St John’s wort was observed to lower plasma concentrations of the protease inhibitor indinavir. In the second report, heart transplant rejection, as a result of the lowering of ciclosporin plasma concentrations below therapeutic levels, followed St John’s wort therapy. It has subsequently transpired that St John’s wort will adversely affect the performance of a number of common drugs by causing their rapid elimination from the body, either by enhanced metabolism or as a result of increased action of the drug transporter P-glycoprotein. Among common drugs so affected are anticoagulants such as warfarin, digoxin, tricyclic antidepressant agents, simvastatin and others.

In the UK, there are currently (2007) no specific restrictions on the sale of St John’s wort as a herbal preparation but it is recommended that professional advice be sought if it is to be taken in conjunction with other medicines.

Isoflavonoids

Isoflavones are found in the heartwood of species of Prunus and in species of Iris, and are particularly abundant in the Leguminosae (e.g. in dyer’s broom, Genista tinctoria). The latter contains genistin (not to be confused with the gentisin of gentian), the 7-glucoside of genistein. Rotenone contained in the roots of Derris and Lonchocarpus species (see Chapter 40) is an isoflavonoid in which the 2,3 double bond of an isoflavone is reduced.

Phyto-oestrogens

Isoflavones, along with coumestans (also flavonoids) and lignans (q.v.), belong to a class of substances known as non-steroidal phyto-oestrogens. Both structurally and functionally they are similar to oestradiol (see Fig. 23.4) and related sex hormones and exert weak oestrogenic effects. They are present in certain foods and herbal remedies and are well-documented as producing infertility in animals as, for example, clover disease in sheep grazing on clovers containing a high phyto-oestrogen content.

Studies provoking much medical and general press attention have centred on the role of phyto-oestrogens as dietary constituents having positive effects in the prevention of cancer, heart disease and postmenopausal symptoms.

Foods containing appreciable quantities of isoflavones are soya beans, soy products and other legume crops; they are also present in the herbs Red Clover Flower BHP (Trifolium pratense) and broomtops (Cytisus scoparius). In the plant they occur free or in the glycosidic form, in the latter case being hydrolysed by colonic bacteria to give the active aglycone; genistein and daidzein are the principal examples, the latter being formed from formononetin (Table 21.5). As plant nutraceuticals, these compounds are more fully discussed in Chapter 32.

A new class of non-steroidal phyto-oestrogens are the prenylated flavonoids. Many of these compounds are known and this activity has been described for 8-isopentenylnaringenin.

Biflavonoids

The first biflavonoid to be isolated was gingetin, in 1929. Now more than 100 are known with a variety of biological activities being reported. Amentoflavone is of wide distribution, e.g. species of Ginkgo, Hypericum, Rhus and together with robustaflavone has been shown to have activity against influenza A virus, HSV-1 and HSV-2 viruses (Y.-M. Lin et al., Planta Medica, 1999, 65, 120).

Allied drug

Vitex negundo fruits are used in Asian medicine and can be distinguished from the BP drug by larger fruits.

Source

Calendula flower derives from the marigold Calendula officinalis L., family Compositae, and is not to be confused with ‘marigold’ referring to Tagetes spp. The EP and BP specify the whole or cut, dried, and fully opened flowers detached from the receptacle and obtained from cultivated varieties. The BHP allows also the whole composite flowers which includes the involucre of bracts.

C. officinalis is a native of Central, Eastern and Southern Europe and commercial supplies are obtained largely from Eastern Europe and Egypt.

Characters

Detailed descriptions for the ligulate florets and the composite flower heads will be found in the BP and BHP respectively. Diagnostic features are the morphology of the ligulate and tubular florets, various biseriate clothing and glandular trichomes (see e.g. Fig. 42.4), pollen grains with a spiny exine, and corolla fragments with yellow oil-droplets, calcium oxalate and fairly large anomocytic stomata.

Constituents

Flavonoids, triterpenoids, essential oil and polysaccharides are the principal constituents of calendula flowers. All groups have been shown to exhibit pharmacological activity and serve to illustrate the difficulty of devising an assay which represents the true therapeutic activity of the drug. The EP and BP determine the flavonoid content, expressed as hyperoside (not less than 0.4%), utilizing the same method as for Birch Leaf. Other assays based on triterpenoid assessment have been described.

The flavonoid mixture involves quercetin and isorhamnetin derivatives. Triterpenoid saponins (calendulosides A–F, see Table 23.5) are glycosides based on oleanolic acid-3-O-β-D-glucuronide and are present in variable proportions (2–10%) depending on time of harvesting and chemotype. The roots are a richer source than the flowers. These saponins have haemolytic and anti-inflammatory activity. Polysaccharides include a rhamnoarabinogalactan (M_r 15 000; rhamnose 24.8%, arabinose 34.2%, galactose 41.0%) and two arabinogalactans with M_r’s of 25 000 and 35 000 (J. Varljen et al., Phytochemistry, 1989, 28, 2379). Antitumour and phagocytosis stimulation properties have been reported for the polysaccharide fraction. At least 15 compounds have been identified in the essential oil.

Other constituents of the flowers are triterpene alcohols (e.g. α- and β-amyrin, calenduladiol, etc.), sesquiterpenes and carotenoids.

Uses

Calendula is used internally for the alleviation of gastrointestinal disorders and externally, as an ointment or lotion, for the treatment of minor wounds and rashes.

Characters

The elder inflorescence consists of small regular flowers arranged in compound umbel-like cymes; calyx superior, 5-toothed; corolla flat, rotate, deeply 5-lobed, creamy white with 5 stamens inserted in the tube; anthers yellow. The flowers have a slightly bitter taste and a sweet, not altogether agreeable odour.

The microscopical characters of the corolla include numerous small oil globules and an upper epidermis with cells having slightly thickened, beaded walls and a striated cuticle. Epidermal cells of the calyx also have striated walls and those at the basal end exhibit unicellular marginal teeth. Calcium oxalate is seen as idioblasts of sandy crystals. There are numerous pollen grains about 30 μm in diameter (as measured in a chloral hydrate mountant) with a faintly pitted exine and three germinal pores and furrows.

Constituents

The drug contains a small proportion (up to c. 0.2%) of a semi-solid volatile oil consisting of free acids, principally palmitic acid, and C₁₄–C₃₁ n-alkanes. By 1985 over 80 components had been identified in the oil.

Flavonoids (up to 3.0%) are predominantly flavonols and their glycosides: rutin predominates with smaller quantities of isoquercetrin, astragalin and hyperoside together with the aglycones quercetin and kaempferol.

Other constituents are triterpenes (α- and β-amyrin principally as esters of fatty acids), triterpene acids (ursolic, oleanolic and 20β-hydroxyursolic acids), various other plant acids (chlorogenic, p-coumaric, caffeic and ferulic acids, (Fig. 19.5), and their beta;- glucosides), sterols, mucilage, tannin and traces of sambunigrin (Table 25.1).

Standards

There are BP/EP limits for discoloured, brown flowers (15%) and for fragments of coarse pedicels and other foreign matter (8%). Thin-layer chromatography is employed as a test for identity with further modification to detect adulteration with Sambucus ebulus. Flavonoids, calculated as isoquercetrin are determined by absorbance measurements at 425 nm.

Allied species

Sambucus ebulus (danewort) is a perennial, foetid glabrous herb with a creeping rhizome and upright little-branched stems. It occurs throughout Europe and apart from habit, is distinguished from S. nigra by obvious ovate stipules. S. canadensis, American elder, is a somewhat smaller tree than S. nigra and is widely spread throughout North America; it is used similarly to S. nigra.

Uses

Elder flowers are administered principally as an infusion or herbal tea for the treatment of feverish conditions and the common cold; it acts as a diaphoretic but the mechanism and constituents involved are unclear. The flowers also have diuretic properties.

It may be noted that the sialic acid-binding lectin present in elder stem-bark extracts finds considerable current use in certain biochemical procedures.

Constituents

Various flavonoids occur in horsetail to the extent of 1.0%, the BP/EP requiring a content of at least 0.3% total flavonoids expressed as isoquercitroside. A major component is quercetin 3-glucoside, also luteolin glycosides in some samples (Fig. 21.18). Chemical races of horsetail involve flavonoids, see M. Veit et al., Planta Medica, 1989, 55, 214. Horsetail also contains a naturally high mineral content, with silicic acid and silicates comprising about 8% of the drug; also present are potassium and aluminium chlorides, all contributing to a high ash value for the drug for which, unusually for crude drugs, the pharmacopoeia sets a minimum, as well as higher limit, viz: total ash within 12–27%, acid-insoluble ash within 3–15%. Alkaloids are usually absent or present in small amounts, but see below for poisonous adulterants. Phenolic acids, saponins and phytosterols are among other reported constituents.

Uses

At one time the high siliceous mineral content of horsetail rendered it useful for the abrasive cleaning of copper and bare wooden objects. Traditionally, it has been used medicinally for its diuretic, haemostatic and astringent properties in particular for genitourinary complaints and externally to assist wound healing.

Allied species

A number of Equisetum spp. grow in similar damp localities to that of E. arvense, including E. sylvaticum the wood horsetail, E. palustre the marsh horsetail and E. fluviatile the water horsetail and might be mistaken or substituted for the genuine drug. As these are known to cause animal poisoning due to the alkaloids, e.g. palustrine and saponins, which have been reported, correct identification of the drug is essential. This is addressed by the pharmacopoeial macroscopic and microscopic descriptions of the drug, briefly covered above, and the TLC test for ‘Other Equisetum species and hybrids’.

Characters

The shortly petiolate leaves are 2–7 cm long with pointed apex, cuneate base, coarsely serrate margin, deep green to yellowish-green upper surface, greenish-grey lower surfaces and, often pigmented pinnate venation.

Microscopical characteristics include wavy-walled, slightly beaded epidermal cells, diacytic stomata more numerous on the lower surface, laminaceous glandular trichomes having in contrast to many other species only four secretory cells, multicellular uniseriate conical clothing trichomes often with reddish contents. The stems afford considerable non-specific vascular tissue.

Constituents

Flavonoids as represented by sinensetin (Fig. 21.18) and various derivatives; diterpenes as illustrated by orthosiphols A–J and other highly oxygenated diterpenes (see S. Awale et al., Chem. Pharm. Bull., 2003, 51, 268); various benzochromenes, including methylripariochromene A in variable amounts and others; volatile oil up to 0.7% and containing β-caryophyllene and its oxide, α-humulene, β-elemene, etc.; caffeic acid and its derivatives, particularly rosmarinic acid; phytosterols such as β-sitosterol; and inorganic salts, particularly potassium at around 3.0%.

The BP/EP requires a minimum content of 0.05% sinensetin for the drug determined by liquid chromatography using sinensetin as the reference compound.

Uses

Traditional uses in Europe invoke the diuretic properties of the drug for the treatment of urinary and kidney problems; in S.E. Asia it is used for the treatment of diabetes and hypertension.

Constituents

Apart from the earlier isolation of stachydrine (formula, see Fig. 26.2), it was in the period 1970–1985 that the major constituents of motherwort were elucidated; these include flavonoids, iridoids, terpenoids and tannins.

Flavonoids include hyperoside, kaemferol-3-D-glucoside, quercitrin and rutin (for formulae of these see Fig. 21.18 and Table 21.5). Iridoids include leonuride (see Fig. 24.1), ajugol and others. Minor alkaloids in addition to the major alkaloid stachydrine include the stereoisomers of its 4-hydroxy derivative (turicin) and betonicine (see formula under ‘Yarrow’). Diterpenes of the labdane type include leocardin and a diterpene similar to marrubiin (q.v.). For the structural determination of three new labdane diterpenes see K. Vijai et al., Planta Medica, 2008, 74, 1288.

The BP/EP requires a minimum flavonoid content for the drug of 0.2% expressed as hyperoside and assayed by absorbance measurements at 425 nm on a hydrolysed extract.

Traditional uses

For nervous tension and menstrual problems. There is some pharmacological support for its use as a uterotonic and for cardiovascular disorders.

Constituents

Isoflavones include the pterocarpan medicarpin (Fig. 21.18) (also a constituent of lucerne), homopterocarpin-7-O-glucoside and trifolirhizin (maackianin-7-O-glucoside); possibly the isoflavone formonoetin and its 7-O-glucoside. Tannins, lectins and triterpenoids, including α-onocerin (α-onoceradiendiol) have also been recorded. Volatile oil (0.02–0.29%), occurring in the entire plant, gives the drug a somewhat unpleasant odour and contains principally anethole, carvone and menthol; among other constituents are methone, camphor and estragole.

The BP/EP identification of the drug includes a TLC test.

Uses

The roots are traditionally used for their diuretic, antilithic and anti-inflammatory properties in the treatment of infections of the urinary tract and in removal of kidney and bladder stones.

Constituents of the fruits

Anthocyanins, particularly glucosides and galactosides of cyanidin, peonidin, delphinidin, petunidin and malvidin (Table 21.6) are responsible for the final colour of the berries. These pigments increase in quantity during ripening whereas that of the polyphenols (−)-epicatechin, (+)-catechin and dimeric proanthocyanidins (Fig. 21.7) decrease. Other constituents include a number of common phenolic acids, vitamin C and volatile compounds. Over 100 volatiles have been identified, the principal ones that afford the characteristic odour of the berries being trans-2-hexenal, ethyl 3-methylbutyrate and ethyl 2-methylbutyrate.

For the dried fruits, the BP/EP specifies a minimum tannin content of 1.0% expressed as pyrogallol and for the fresh fruits a minimum of 0.30% anthocyanins expressed as cyanidin-3-glucoside chloride. The latter is determined by absorption measurements at 528 nm on an acidified aqueous extract of the dried fresh berries. The loss on drying of the fresh berries is 80–90%.

Frozen fresh berries should be stored at or below −18°C. It is important to inspect the dried drug for insect and mouldiness.

Uses and actions

Bilberry has many traditional medicinal uses, a number of which have been supported by fairly extensive pharmacological research. For detailed references, the reader should consult J. Barnes et al., Herbal Medicines, 2nd edn. 2002, p. 73, The Pharmaceutical Press, London. See also P. Morazzoni et al., Fitoterapia, 1996, 66, 3 for an overall review of bilberry.