Abstract The present Ph. D. thesis comprises two parts, Part A and Part B. The Part A describes the isolation and structural elucidation of a new flavonoid and two new natural amines from the whole plant of Onosma hispida Wall. In addition to this eleven known compounds have also been isolated for the first time from this species. -----------------------------------------------------------------Snaps--------------------------------------------------------- Known compounds isolated for the first time from Onosma hispida 1. 5, 2'-Dihydroxy-7, 5'-imethoxyflavone (46) 2. Apigenin (47) 3. 3,5,7 - Trihydroxy-6,4' -dimethoxyflavone (48) 4. 3,5,4' -Trihydroxy-6,7-dimethoxyflavone (49) 5. Apigenin 7-O-β-D-glucoside (50) 6. Benzoic acid (51) 7. 4-Hydroxybenzoic acid (52) 8. 5,4' -Dihydroxy-3,6,7-trimethoxyflavone (53) 9. 5-Hydroxy-3,6,7,4' -tetramethoxyflavone (54) 10. Methyl 4-methyltetradec-9-enoate (55) 11. Methyl 4-methyltetradeca-9, 12-dienoate (56) The compounds isolated from Onosma hispida were screened against various clinically important enzymes studied in the enzymology section of our Institute, including acetyl- and butyryl cholinesterase and lipoxygenase. SAR studies were also carried out in case of the enzyme lipoxygenase inhibitors. The results are described in Tables-13 and -14. The Part B describes the isolation and structural elucidation of three new iridoids, a new sesquiterpene, a new steroidal galactoside and three new long chain aryl esters from the whole plant of Buddleja crispa Benth. In addition to this eight known compounds have also been isolated for the first time from this species. -----------------------------------------------------------------Snaps--------------------------------------------------------- Compounds isolated for the first time from Buddleja crispa 1. β-Sitosterol (275) 2. Ursolic acid (276) 3. Genipin (277) 4. β -Gardiol (278) 5. Buddlejoside A2 (279) 6. Buddlejoside As (280) 7. 1-Heptacosanol (281) 8. Methylbenzoate (282)
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