(Photo; Rauwolfia tetraphylla an alternative to R. serpentina)
A number of medicinal plants are on the verge of extinction due to overexploitation caused by an increasing demand. Many of us would be knowing that biologically related plants having similar flowers, fruits, phytochemicals etc or in other words, plants of same family, produce same or similar compounds, just like the “blood relationships” of humans and animals. That is why Chemotaxonomists (Taxonomists assessing relationships based on the chemicals in plants) are doing to find out the kinship among plants. Thus all plants in the family Menispermaceae would have isoquinoline alkaloids like that of Amruta (Tinospora) and those of Solanaceae contain Datura alkaloids like atropine or related compounds. Thus we can find out an alternative source plant among the closest relatives of a threatened medicinal plant from among the tribe, subfamily or family where it belongs and this process is known as Bioprospecting. Once the related plants are selected we have to screen that plant/s for the same or similar compounds, pharmcological properties and side effects, if any.
Classic cases of bioprospecting : Rauwolfia and Taxus
Rauwolfia serpentina (Sarpaganddha) is a threatened plant and it is very difficult to get a large amount of its roots for commercial manufacturing of medicines based on it. But another species of genus Rauwolfia, i.e. R. tetraphylla, is found to have the same alkaloids (of R. serpentina) but containing more of deserpidine, which possesses the same activity of reserpine but without the side effects. Another classic example of bioprospecting is seen in genus Taxus, a conifer. The antileukemic diterpenoid Taxol was reported from the bark of Pacific/Western yew (Taxus brevifolia) and one needs the bark of at least 7 full-grown trees to isolate 1g of Taxol. But in India we have Taxus baccata/T.wallichiana (in Sikkim Himalayas) which is found to contain taxol and another diterpenoid baccatin in “leaves” which could semisynthetically be converted to Taxol by a few steps. The advantage with T. baccata is that taxol/baccatin is obtained from leaves which can be harvested periodically without harming the tree (In T. brevifolia, the removal of bark endangers the life of tree.)
If you see a chemotaxonomic classification (like that of A. Cronquist or my classification which I proposed in my book on Taxonomy) every family is described with its specific group of phytochemicals and with a list of plants having medicinal and other uses.
Bioprospecting potential = Plants which are potential sources of valuabe phytochemicals and are yet to be screened (At a glance)
1. Acetogenins in Annonaceae, Anticancer and biopesticides
Plants studied so far = 15-20; Remaining plants 2300
2. Limonoids and quassinoids. treatment for leukemia, breast cancer, induce apoptosis, antipyretic, anti microbial, anthelmintic, skin diseases. Oils with them are used in rheumatism and leprosy and best Biopesticides
Plants studied: 15-20 only ; Plants remaining 1979
3. Ergot alkaloids like Ergotamine, Ergotoxine and Clavine alkaloids, Morning Glory seeds, Argyreia, Rivea, Convolvulus, Evolvulus
Plants studied 25-30 Remaining Convolvulaceae : 1450
4. Isoquinoline alkaloids as seen in Berberis, Alangium, Tinospora: Poppy, Tiliacora:
Plants rich in isoquinolines; Ranales : 3200; Papaverales : 600
5. Sulphur containing glycosides, Glucosinolates and isothiocyanates, The best antioxidants and antinicrobials..
Brassicaceae=3250, Capparaceae = 625
6. Sulphides of Garlic like ajoene, allyl propyl disulphide, diallyl sulphides, Allicin etc.
• Plants which are potential sources, Liliaceae = 4950
7. Isoflavonoids Genistein/Genistin – for breast cancer, used in stent coating, Rotenones = very important biopesticides (harmless to humans)
Plants screened 50 Plants remaining Members of Fabales = 17200
Others
• Lupinane alkaloids in Fabaceae,
• Tropolones in Liliaceae,
• Amaryllidaceous alkaloids in the Amaryllidaceae,
• Biflavones in Coniferales and Clusiaceae,
• Non-protein amino acids in Fabaceae,
• Erucic acid in the Brassicaceae (Cruciferae),
• Petroselinic acid in the Apiaceae (Umbelliferae),
• Polyacetylenes in the Asteraceae (Compositae)
• Hydnocarpic and chaulmoogric acid in the Flacourtiaceae,
• Hypoglycine in the Sapindaceae,
• Xanthones in the Gentianaceae,
• Peptide alkaloids in the Rhamnaceae etc.
Interested persons may go through the books mentioned below.
References;
1. Arthur Cronquist (1981) An Integrated System of Classification of Flowering Plants, Columbia University Press, New York.
2. Mammen Daniel (2009) Taxonomy: Evolution at Work, Alpha Science International, Oxford, UK.(Indian Edition by Narosa Publishers, New Delhi.)
Mammen Daniel
