Abstract The work presented in the thesis deals with the isolation, structure elucidation and study of pharmacological properties of the four plants. Investigation on the chemical constituents of each plant is discussed in separate parts. 1) PART-A It describes the studies on the chemical constituents of the leaves of Rhazya Stricta, which have led to the isolation of two new indole alkaloids (i,ii) with six known alkaloids (iii-viii) which are as follows Rhaziattarine (64) Hexahydroalstonine (70) Akuammidine (71) Rhazimine(72) N-acetyl aspidosphermidine(73) Eburnamenine(74) Strictamine (75) Rhazimanine(76) 2) PART-B It deals with the investigation on the chemical constituents of roots of Taxus baccata,, which led to the isolation of two new taxane diterpenoids (i,ii)and three known diterpenoids (iii-v) (i)Taxa-4(20), 11.diene-10-methoxy-2a,5a-diacetoxy-14b,a-methyl butyrate {116} (ii) Taxa-4(20),11-diene-2a-5a, 10B triacetoxy-14Bya methyl butyrate {117} iii)Taxusin {118) (iv)2-Deacetoxy taxini J {119} (v)7B-acetoxy taxusin {120} 2) PART-C It describes the studies on the chemical constituents of Fritillaria persice This led to the isolation of one new (i) and two known alkaloids isolated for the first time from F.Persica (ii-iii). (i)Persinin {137) (ii)Delavinone (138) (iii)Delavine (139) 4) PART-D It deals with the investigation carried on the chemical constituents of Zizyphus lotus.which led to the isolation of one new cyclopeptide alkaloid. (i)Lotusinin {149} Extensive aspectroscopic techniques such as EIMS, FDMS, FAMBS,HRMS,Peak matching MS,UV,IR,1H and 13 C-MMR (BB,DEPT)COSY.45 , NOE difference HMBC and HMOC were employed to elucidate the structures of the above compounds.
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