Before any herbal medicine is screened for testing, phytochemical investigations are essential because sometimes a critical constituent is missing from the herb due to reasons like storage, geographical distribution or processing. Today standardized extracts are used in herbal drug industry and their standard is based on the presence of marker compounds. The marker compounds may or my not have pharmacological activity.
A brief account of type of the phytochemicals distributed in plant flora is given below:
1. Alkaloids are basically nitrogen bases and the most important class of phytochemicals. The amino acids act as building blocks for the biosynthesis of alkaloids.
2. Bitter principles are basically glycosides and are found commonly in plants of Genitiaceae. The bitters act on gustatory nerves, which results in increased flow of saliva and gastric juices and acts as appetizers.
3. Phenolic compounds are widely distributed in plant flora. A variety known as polyphenols is found in fruits of some plants. They occur as natural colour pigments and are responsible for the colour of the fruits.
4. Diarylheptanoids are rare compounds found in the family Zingiberaceae. Recent animal studies have shown diarylheptanoids to be potent anti-inflammatory agents.
5. Flavonoids are important group of polyphenols, widely distributed in plant flora. 4,000
flavonoids are known to exist and some of them are pigments in higher plants. Quercetin,
kaempferol and quercitrin are common .Soya flavones have recently gained importance due to variety of pharmacological activities.
6. Furanocoumarins are photosensitizing agents used in the treatment of pigment disorders. Ayurveda, the ancient science of India, has described the use of bawachi (Psoralia corylifolia) for the treatment of leucoderma.
7. Furochromones are group of coumarins, derived from benzopyrone. They are related to furanocoumarins.
8. Hydroxycoumarins represents another group of coumarins.
9. Glycosides are water-soluble constituents, found in the cell sap. They are colourless,
crystalline substances containing carbon, hydrogen and oxygen. Some glycosides are
peculiar in having nitrogen and sulphur.
10. Napthodianthrones are derivatives of anthracene.
11. Neutral principles are bodies of unidentified character.
12. Acylphloroglucinols are group of phenolic compounds having significant antidepressant activity.
13. Resins are brittle, non-volatile, solid substances. Oleoresins are natural products of resin mixed with volatile oils. Gum- resins are plant exudates and are mixtures of gum and resin and often volatile oils. Balsams are combinations of resins or oleoresins with aromatic acids.
14. Saponins are glycosides found in number of plants. They are poisonous.
15. Sesquiterpene lactones constitute significant group of phytochemicals. They are formed by condensation of three isoprene molecules followed by oxidation.
16. Sterols are derivatives of steroids. Modern clinical studies have supported their role as anti-inflammatory and analgesic agents.
17. Tannins are widely distributed in plant flora. They are phenolic compounds of high
molecular weight.According to one estimate, only 20 percent of the plant flora has been screened for drugs. Keeping in view the vast treasure of medicinal herbs, one can expect phytochemicals to play a significant role as modern science has limited options for diseases like diabetes mellitus, rheumatoid arthritis, Alzheimer’s disease and Parkinson’s disease. Work on the identification and isolation of phyochemicals is an ongoing process and herbal medicine is expected to play critical role in the future healthcare system.
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