CHEMICAL INVESTIGATION OF SOME PLANTS OF MEDICINAL IMPORTANCE

Abstract

From the beginning of human civilization, man has been dependent upon plants for food, fibres, timbers, medicines and a host of other useful products. From times immemorial the crude extracts of several plants had been used as medicines in the treatment of various ailments and diseases and there was no ailment known which could not be cured by these crude extracts of plants. This knowledge about medicinal plants led to the development of two well known indigenous systems of Ayurvedic and Unani medicines. There are a large number of references mentioning the therapeutic uses of more than 700 plants recorded by Susruta Samhita, Charaka and Vagbhatta. Until the last century, it was not known why certain plants possessed curative properties. However, in the last few decades, with the introduction of sophisticated instruments and efficient techniques, the isolation, purification and structural elucidation of chemical constituents responsible for the therapeutic activities of plants became possible and a systema tic phytochemical investigation could be carried out for understanding structure-activity relationships resulting in useful drug-designs and subsequently a large number of drugs could be synthesised with improved biological activity and less toxicity. Although a large number of Indian plants have been investigated leading to the discovery of several efficient drugs, there is still an ample scope of carrying out a (ii) systematic chemical examination of uninvestigated and unexploited plants for proper utilization of natural wealth towards industrial,scientific, pharmaceutical and medicinal purposes to strengthen economic and industrial development of this country. It was, therefore, thought worthwhile to undertake a systematic and detailed chemical investigation of some medicinally important plants of local region. Four plants namely Boerhaavia diffusa Linn (fam: Nyctaginaceae), Phyllanthus nirurii Linn (fam: Euphorbiaceae), Launaea asplenif olia Hook (fam: Compositae) and Aster acantha lonqifolia Nees (fam: Acanthaceae) were selected for the study as litera ture survey reveals that only very little work seems to have been dene so far on these plants. The present thesis incorporates results of chemical investigation on the isolation and characterization of chemical constituents of the 3bove plants namely steroids, triterpenoids.flavonoids and their glycosides. Four hitherto unknown compounds have been isolated and their structures have been conclusively established. A new C-methylflavone has been isolated from the roots of Boerhaavia diffusa Linn which has been characterized as 5, 7 - dihydroxy- 3 , 4*- dimethoxy- 6,8-dimethylflavone (Chapter_2 ). Two new flavoncids have been isolated from Phyllanthus nirurii Linn. They were characterized as fisetin-4 -glucoside and a new prenylated flavanone glycoside, designated as nirurin. The structure of nirurin has been suggested as 5,6,7,4 - tetrahydroxy-8- (3-methylbut-2-enyl) flavancne-5-O-rhamnoglucoside (Chapter-3). (iii) The fourth compound has been isolated from Launaea asplenifolia Hook, which has been characterized as 5,7, » i » 3 ,4 ,5 -pentahydroxy-3-(3-methylbutyl) flavone and has been designated as asplenetin. Its glycoside has also been isolated and characterized as asplenetin-5-O-neohesperidoside and designated as asplenin (Chapter-4). The thesis has been divided into five chapters. The first chapter is an introductory one dealing with the importance and development of plant chemistry in India, general important techniques employed for the isolation, purification and characterization of plant constituents as well as an account of the classes of compounds discussed in the thesis. The second chapter deals with the chemical investigation of the roots of Boerhaavia diffusa Linn which is used in dropsy, jaundice, anaemia and Urinogenital infections. It was collected from Saharanpur(U.P) region in the month of April, dried and extracted with ethanol. The extract after concentration was resolved into pet.ether, chloroform and ethyl acetate soluble fractions. The pet ether extract on chromatography over silica gel using pet ether, benzene and ethyl acetate as eluants afforded three compounds namely, Octacosanoic acid, e-sitosterol and ursolic acid while the latter two fractions yielded a new flavone which was characterized as 5, 7- dihydroxy- 3,4- dimethoxy- 6,8- dimethyl flavone. The third chapter describes the chemical examination of phyllanthus nirurii Linn which is used in jaundice, dropsy and Urinogenital infections. It was collected in the month of (iv) September, dried and extracted with pet ether and ethanol. The patrol extract on chromatography over silica gel afforded three compound namely, octadecanol, octacosanoic acid and P-sitosterol. The ethanolic extract was repeatedly extracted with ethyl acetate which on removal of the solvent was resolved intc chloroform and methanol soluble fractions. The chloroform fraction gave kaempferol, quercetin, naringenin and chrysoeriol en chromatography over silica gel while the methanol soluble fraction yielded seven flavonoid glycosides namely, astragalin, quercitrin, isoquercitrin, rutin, isorhamnetin 3-o-galactoside and two new flavonoids, characterized as fisetin-4 -O-glucoside t and 5,6,7,4 -tetrahydroxy-8-(3-methylbut-2-enyl) flavanone-5-Orutinoside. The latter has been designated as nirurin. Its aglycone i.e. 5,6,7,4 -tetrahydroxy-8-(3-methylbut-2-enyl) flavanone has been designated as nirurinetin. The fourth chapter incorporates the results of chemical investigation of Launaea asplenifolia Hook which has been used as a lactagogue. The whole plant was collected in the month of March, dried and extracted with ethanol. The extract was resolved into pet ether and ethyl acetate soluble fractions. The pet.ether fraction afforded two compounds namely, octacosancic acid and lupeol. The ethyl acetate soluble fraction was again resolved into chloroform and methanol soluble portions. The chloroform soluble portion gave 7-hydroxy-3 ,4 -dimethoxy flavone, luteolin, apigenin and a new flavone designated as asplenetin and characterized as 5,7,3 ,4 ,5 -pentahydroxy-3- (3-rnethylbutyl) flavone, while methanol soluble portion (v) afforded vitexin, apigenin-7-0 glucoside, luteolin -7-0- glucoside, delphinidin and a glycoside of this new flavone which has been characterized as asplenetin-5-0-neohesperidoside and designated as asplenin. The fifth chapter deals with chemical investigation of Asteracnntha lonqifolia Nees which is used in gonorrhoea, jaundice and rheumatism. It was collected in the month of October, dried and extracted with ethanol. The extract on evaporation of the solvent was extracted with petroleum ether, which on chromatography afforded three compounds namely, lupeol, betulin and stigmasterol. It was also observed that betulin was absent in the aerial parts while stigmasterol was absent in roots of this plant. The constituents obtained from the above plants were characterized by physico-chemical methods such as IR,UV,NMR and mass spectroscopy. For characterization of flavonoids, UV spectra were recorded in methanol using various diagncsitic reagents such as NaoMe, A1C13, AlCLj/HCl, NaO*c and NaOAc/H3Bo3 and observing the characteristic shifts in wave lengths. The structures of the compounds were substantiated by degradation, oxidation and preparation of suitable derivatives wherever possible. The final confirmation was made by their comparison with authentic samples.