Cytotoxic and anti-microbial constituents from some Bangladeshi Bridelia and Erythrina species

Abstract

This thesis describes the isolation and structure elucidation of secondary metabolites from four plants Bridelia verrucosa, B. stipularis, B. tomentosa (Family: Phyllanthaceae) and Erythrina fusca (Family: Fabaceae) as well as biological studies of the extractives from these plants along with E. variegata (Family: Fabaceae). A total of nineteen compounds were isolated of which three appear to be new. The structures of the isolated compounds were elucidated mainly by spectroscopic studies including high field NMR. The stem bark of B. verrucosa afforded eight compounds viz. glochidonol (BVSP-1, 46), brassicasterol (BVSP-2, 47), friedelin (BVSP-4, 48); 5β-24S-ethylcholestan-3β-ol (BVSP-6, 49); stigmasterol (BVSP-34, 50); 5,5'-dihydroxysesamine (BVBC-2, 51), 3-ketoleanane (53) and pinoresinol (BVS-65, 54). Except stigmasterol (50) and pinoresinol (54) this is the first report of the isolation of compounds 46-49, 53 and 54 from the genus Bridelia and 51 has been identified as a new natural product. Phytochemical investigations of methanolic extract of the stem bark of B. stipularis provided two triterpenes namely, glut-5(6)-en-3-one (BS-01, 55), glut-5(6)-en-3α-ol (BS-06, 56) and a cholestane type compound (22E)-7-hydroxy-28methylcholesta-4,22-dien-3-one (BS-11, 57). All these are the first report of their occurrence from B. stipularis while (22E)-7-hydroxy-28-methylcholesta-4,22-dien-3-one is a new compound. On the other hand, phytochemical investigation of methanol extract of the stem bark of B. tomentosa yielded friedoolean-5(6),14(15)-dien-3-one (BT-1, 58), β-taraxerol (BT6, 59), D -stigmasterone (BT-8, 60) and lupeol (BT-14, 61). This is the first report of their occurrence from this plant and friedoolean-5(6),14(15)-dien-3-one (58) is a novel compound. The carbon tetrachloride soluble fractions of a methanol extract of the stem bark of E. fusca provided three flavonoids namely, shinpterocarpin (EF-7, 62), lupinifolin (EF-8, 63) and 3,9dihydroxy-4-(3,3-dimethylallyl)[6aR,11aR]-pterocarpan (64) and a steroid, β-sitosterol (EF38, 65). All these are the first report except 65 from E. fusca. The crude extracts and organic soluble material of the investigated plants and some purified compounds were screened for their antimicrobial activity against a wide range of Grampositive and Gram-negative microorganisms and fungi by the standardized disc diffusion method. Kanamycin and Griseofulvin were used as reference drugs for the test.