4.1.4.3 Comprising of ‘O’ into Heterocyclic Rings: There are a number of natural plant
constituents that essentially possess an oxygen atom into the heterocyclic ring-system. A few typical example are cited below to initiate some commendable interest in the domain of “phytochemistry”:
4.1.4.3A Furan-based Constituents: These constituents are derived from five-membered
heterocyclic ring ‘furan’, namely:
(a) Furfural (or 2-Furfuraldehyde): It is a heterocyclic aldehyde that usually occurs in the first fraction of many essential oils, belonging to the natural order-Pinaceae, for instance: Pinus palustris (Pine oil) and cade oil. It is also present in oil of orris rhizome, clove oil, petit-grain, lavender and cinnamon oils.
4.1.4.3B Pyran-based Constituents: They are derived from six-membered heterocylic ring ‘pyran’, namely:
(a) Dicoumarol (Syn: Dicoumarin: Dufalone; Melitoxin;): It was originally isolated from sweet clover (Improperly cured Mililotus hay).
(b) Umbelliferone (Syn: Hydrangin; Skimmetin;): It is present in many plants and obtained by the distillation of resins belonging to the natural order Umbelliferae. It is the aglucon of skimmin.
(c) Meconic Acid (Syn: Oxychelidonic acid): It is obtained from opium i.e., Papever\ somniferum which contains 4 to 6% of meconic acid.
(d) Coumestrol: An estrogenic factor occuring naturally in forage crops, especially in ladino clover (Trifolium repens L.), strawberry clover (T. fragiferum) and alfalfa (Medicago sativa L.).
4.1.4.3C Flavan based Constituents:
(a) Caechin (Syn: Catechol; Cyanidol): It is a flavonid found primarily in higher woody plants as (+)–catechin along with (–)–epicatechin (cis-form). Source: From mahogany wood and catechu (gambir and acacia).
(b) Leucocyanidin (Syn: Flavan; Leucocyanidol): It is obtained from the petals of Asistic cotton flower (Gossipum spp.) Stephens; Butea frondosa Koen ex Roxb. and taxifolin.
4.1.4.3D Phenylbenzopyrilium based Constituents:
(a) Cyanidin Choride: It is isolated from bananas and prepared by the reduction of quercitin.
4.1.4.3E Carbohydrates: There are several examples of well known compounds belonging to the carbohydrates:
(a) Glucose: It occurs naturally in the free state in fruits and other parts of plants, it is also found in the combined form in glucosidase, in di- and oligosaccharides, in the polysaccharides (cellulose and starch) and in glycogen.
REFERENCES
Ashutosh Kar (2003), Pharmacognosy and Pharmaco biotechnology, 2nd Edition
‘Handbook of Medicinal Herbs’ (2001), J.A. Duke, CRC-Press, London, 1st Edn.
William Charles Evans (2002), Trease and Evans Pharmacognosy 15th Edition by: Trease, Bailliere Tindall; Evans.
Ramstad (1956), E., ‘Modern Pharmacognosy’, McGraw Hill, London.
