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The constituents of medicinal plants - Pengelly A.

Pengelly A. The constituents of medicinal plants - London, 2001. - 109 p.
Download (direct link): theconstituents2001.djvu
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Allyl sulphides
These are a group of sulphur compounds based on the “allyl” group (СНг=СНСН2) which are found in garlic -Allium sativa, onion - Л сера, and other members of the Allium genus (Liliaceae). Their common precursor is the sulphur-containing amino acid cysteine. The complex chemistry of garlic and onions is best reviewed by Eric Block (1985) and more recently by Sendl (1995). Extraction techniques using different solvents has assisted in identification of oxidation and decomposidon products of garlic and onions. These include: diallyl disulphide - product of steam distillation of garlic
О allicin - the oxide of diallyl disulphide, and source of
И garlic odour
ajoene - formed from decomposition of allicin allicin lacrimatorv factor - converted from precursor by
enzymic action when slicing onion [Block 1995].
Apart from antimicrobial properties noted above, allyl derivatives such as ajoene have demonstrated activity against platelet aggregation, inhibition of proinflammatory prostaglandins, antitumor and hypoglycaemic effects [Reuter 1995].
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RESINS
Resins are solid, brittle substances secreted by plants into special ducts, often as a response to damage to the plant by wounding, wind damage etc. Their main role appears to be protection of the plant from attack by fungi and insects. Resins are difficult to classify because of their amorphous nature, they are complex mixtures which include lignans, resin acids, resin alcohols, resinotannols, esters and resenes [Tyler 1988J.
Resins are insoluble in water but soluble in alcohol, fixed oils, volatile oils. They are heavier than water and volatile oils, and have high boiling points. They are translucent and burn with a characteristic smoky flame - hence their use in incense. They have fixative actions hence their use in crafts and industry.
While classifying individual resins is difficult, they are sometimes classified as mixture with other plant constituents eg. gum-resins, oleo-gum-resins, glycoresins. One of the most well known resins comes from the Pinus genus (Pinaceae) and is known as rosin. This amber coloured resin is mainly used in varnishes and other industrial products.
Balsams
These are resinous mixtures that contain cinnamic and/or benzoic acid or their esters.
Benzoin
This balsamic resin is derived from the bark of Styrax benzoin (Styraceae) trees in S.E. Asia. Benzoin contains cinnamic, benzoic and triterpene acids. Its action is antiseptic, stimulant, expectorant, diuretic and antifungal. It is used as a food preservative as well as an ingredient in pharmaceutical preparations such as Whitfield’s Ointment (with salycilic acid) for ringworm, athletes foot [Tyler 1988].
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tetrahydrocannabinol
Podophyllin
Derived from dried rhizomes and roots of Podophyllum peltatum (Berberidaceae), a plant which originates in the forests of central and eastern USA.
Contains 3.5-6% podophyllin resin consisting of the lignans: podophyllotoxin 20% a & b peltatin 15% - purgative principle + lignan glycosides (lost during preparation of resins)
Podophyllin powder has a peculiar bitter taste and is highly irritating to mucous membranes, especially of the eyes. Its caustic nature is utilized in the form of topical applications for warts and condylomas. Internally it acts as a drastic though slow acting purgative. It is also anti-mitotic, ie. stops cell divisions and is sometimes used in leukemia, but problems with side effects limits its use.
Kava Kava - Piper methysticum (Piperaceae)
This large shrub is widely cultivated in Oceania. The dried rhizome and root are used in preparation of an intoxicating beverage. Kava contains 5-10% resin, made up of lactones known as kava pyrones - kavain C14H14O3; methysticin
C14H15O3.
Kava pyrones are potent, centrally acting skeletal muscle relaxants. The action is hypnotic; antipyretic; sedative; local anaesthetic; smoothe muscle relaxant; antifungal. No interaction with benzodiazepine drugs or with moderate consumption of alcohol occurs, nor does kava impair mental alertness. However continually chewing the root can desUoy tooth enamel, and eventually becomes habit-forming [Bone 1994].
Cannabis
Cannabis resin or Indian hemp is derived from dried flowering tops of pistillate plants of Cannabis sativa and C. indica (Cannabaceae). The plants contain 15-20%
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resin consisting mainly of Д9-tetrahydrocannabinol or THC. THC is technically a benzotetrahydropyran and its structure derives from both phenolic and terpenic precursors [Bruneton 1995].
THC is a lipophilic compound which is quickly absorbed but slowly excreted. It is responsible for most of the pharmacologic actions of Cannabis. Therapeutically it is euphoric, sedative, anti-nauseant, appetite stimulant, bronchodilator and reduces intra-ocular pressure in glaucoma. However legal restrictions mean that most use of the herb is illicit. The euphoric effects of the herb are well documented, as are the psychological dependence and disruptive effects on memory and cognitive processes. Its use has also been linked to infertility [Sethi 1991). However acute toxicity is very low and there are no documented cases of fatalities from Cannabis use [Bruneton 19951.
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