Abstract This thesis describes phytochemical investigations on the chemical constituents of two plants: Silene conoidea and Stocksia brahuica and resulted in the isolation and characterization of nine new natural products and a new derivative prepared synthetically. In addition to new constituents, 21 known compounds have also been isolated and characterized for the first time from these species. The new constituents isolated from Silene conoidea are conoidene (1),8(4”-o-α-L-rhamnopranosyl)-C-β-Dglucopyranosylidiosmetin (2),8(4”-o-α-L-rhamnopyraosyl)-C-β-D-glucopyranosylapigenin (3) and from Stocksia brahuic are ethyl 3, 5-dihydroxy-4-methoxybenzoate (8), 2-hydroxy-3-methylbenzoic acid (9), diphenylacetic acid (10), brahol (22) and methyl α-D-fructoside (23). A new synthetically prepared derivative is braholpentaacetate (22a). The new source coumpounds isolated from S. conoidea are α-spinasterol (4), α-spinasterolglucoiside (5), D-pinitol (6), sucrose (7) and from S. brahuica are 3, 4, 5-trihydroxhbenzoic acid (11), 3, 4, 5-trimethoxybenzoic acid (12), methyl 4-hydroxy-3, 5-dimethoxybenzoate (13), ethyl 3, 4, 5-trihydroxybenzoate (14), methyl 4-hydroxybenzoate (15), n-propyl 4-hydroxybenzoate (16), methyl p-hydroxycinnamate (17), brahene (18), 3-O-rutinosyl-3’, 4’, 5, 7-tetrahydroxyflavone (19), 7-hydroxy-6-methoxycoumarin (20), α-tocopherol (21), ethyl β-D-glucoside (24), sucrose (25), pimaric acid (26), isopimaric acid (27), stigmasterol (28), stigmasterolglucoside (29), β-sitosterol (30) and β-sitosterolglucoside (31). The structure elucidation of all compounds was carried out b using different spectroscopic techniques including 1H-NMR, 13C-NMR, DEPT, HMQC, HMBC, COSY-45°, nOe, EI, CI, FD, -ve and +ve FABS, IR, UV etc.
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