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Title: Phytochemical and pharmacological investigation of some medicinal plants
Author: Habtemariam, Solomon
ISNI:       0000 0001 3523 3662
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 1992
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This thesis describes phytochemical and biological/pharmacological studies on six medicinal plants. Plant materials were extracted by ethanol, tested for their biological activity and then subjected to "bioassay-guided fractionation" to yield active and inactive compounds. The compounds were identified by standard physico-chemical techniques including UV, IR, NMR and ElMS. The crude ethanol extract of the leaves of Premna shcimperi was found to be antibacterial against gram positive bacteria (Staphylococcus aureus and Bacillus subtilis). An antibacterial bioassay-guided fractionation of the extract resuited in the isolation of the active principle, (5R,8R,9S,10R)-12-oxo-ent-3,13(16)- clerodien-15-oic acid (SHM-l). This novel compound was bactericidal against S. aureus and B. subtilis at concentrations of 25 and 50 µg ml⁻¹. Studies on the structural-activity relationship of SHM-l showed that the α,β unsaturated moiety played a major role in its antibacterial activity. Investigation of the inactive fractions of P. schimperi extract afforded three flavonoid aglycones: luteolin, quercetin and kaempferidej three flavonoid glycosides: luteolin-4" -,β-D-glucoside, quercetin-3-,β-D-galactoside and quercetin-α-L-arabinopyranoside and five cinnamate and benzoate derivatives. The ethanol extract of the leaves of Premna oligotricha was also found to be antibacterial against a range of gram-positive bacteria. A bioassay-directed isolation afforded three novel active principles, two diterpenes: 16-hydroxy-clerod- 3,13(14}-diene-15,16-olide (SHM-3) and ent-12-oxolabda-8,13(16}-dien-15-oic acid (SHM-S) and a sesquiterpene, 7-α, hydroxy-2-oxo-6,11-cyclofarnes-3(15)-ene (SHM-19). While the activity of SHM-5 and SHM-19 was marginal that of SHM-3 was good, almost comparable with streptomycin. The antimicrobially inactive fractions of P. oligotricha extract yielded a novel diterpene, ent-8,β12α-epidioxy- 12,β-hydroxlabda-9(11), 13-dien-15-oic acid γ lactone and two novel flavonoids: 3,5,5'-trihydroxy-6,7 ,3' ,4'-tetramethoxyflavone and 3,5,7 ,5'-tetrahydroxy-6,3',4'- trimethoxyflavone. Investigation of the leaves of Premna recinosa afforded six flavonoids: quercetin, luteolin, pachypodol, chrysosplenol-D, naringenin and eriodictyol and three lignans: {+)-8-hydroxy-pinoresinol, {+)-lariciresinol and {-)-seco-isolariciresinol. Portulaca oleracea and Pentas schimperiana are used in the folk medicine as local anaesthetics. Studies on the isolated nerve and/or muscle preparations showed that extracts do block nerve conduction in these excitable tissues. A subsequent systematic bioassay-guided fractionation of crude extracts showed that excess potassioum ions in the extracts were responsible for the in vitro pharmacological activity of P. oleracea and P. schimperiana. Extracts from the leaves of Leonotis ocymifolia var raineriana showed no antibacterial activity. Three novel diterpenes: ent- {13S)-9,13α-epoxylabda- 6{ 19),β,16{15)-diol dilactone, (13R)-6,β-acetoxy-9, 13α-epoxylabda-19(20),8,16{ 15)- diol dilactone and 20,8-acetoxy-9α,13e-dihydroxy-15(16)-epoxy-Iabd-14-en-6,19,(β- O-lactone together with a known compound: {13S)-20,β-acetoxy-9,13α-epoxylabda- 6(19),β,16{15)-diol dilactone were isolated. Investigation of the root afforded two known compounds 3-methoxy-4-hydroxy-{trans)-cinnamaldehyde and 3-methoxy- 4-hydroxy-bezaldehyde.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Pharmacology & pharmacy & pharmaceutical chemistry