Browsing by Author "Christopher, Robert"

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    Antimycobacterial, antioxidant and other secondary metabolites from heritiera littoralis and Sonneratia alba
    (University of Dar es salaam, 2012) Christopher, Robert
    This thesis reports results of phytochemical investigations of secondary metabolites from mangrove species Heritiera littoralis Dryand and Sonneratia alba Smith. The studies aimed to establish antimycobacterial, antioxidants and other chemical constituents from two plant species so as to provide information on biomedical plant constituents and contribute to scientific knowledge. In this study, the leaves of H. littoralis yielded a new flavonoid glycoside 3''-Cinnamoyltribuloside, known flavonoid glycosides afzelin, astilbin and tribuloside as well as two pentacyclic triterpenoids 3β-Taraxerol and friedelin. The leaves of S. alba gave a hitherto unreported unusual flavonoid that was trivially named sonneratone. Structures of isolated compounds were elucidated based on spectroscopic data. The pure compounds except 3β-Taraxerol and sonneratone (the latter was not tested) exhibited in vitro antimycobacterial activity against two non-pathogenic mycobacteria species Mycobacerium madagascariense (DSM 44641) and M. indicus pranii (DSM 45239). The flavonoid glycosides exhibited high DPPH (1,1-Diphenyl-2-picrylhydrazyl) radical scavenging activities. These results demonstrate that some of compounds from investigated mangrove species are potential antimycobacterial and antioxidant leads for drug development and/or food supplement. The isolation of secondary metabolites which have proved to be of invaluable antimycobacterial and antioxidant efficacy from investigated mangrove species in this study shows that the two species are good sources of biologically active constituents, from which further studies may lead towards unraveling more interesting compounds.
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    Chemical constituents, antitrypanosomal, antiplasmodial and antimicrobial activities of extracts from selected diospyros, millettia and annonaceae species.
    (University of Dar es Salaam, 2018) Christopher, Robert
    This thesis reports on phytochemical investigations of methanol extracts of root bark, leaves and stem bark from 13 Tanzanian plant species selected for the study from the genera Diospyros and Millettia as well as from the family Annonaceae. The antitrypanosomal assay of methanol extracts carried out against Trypanosoma brucei brucei exhibited activities with IC50 values ranging from 1.28-7.85 g/mL. The antiplasmodial assay of methanol extract carried out against Plasmodium falciparum showed activities with IC50 values ranging from 4.55-24.22 g/mL. The antimicrobial assay of methanol extracts tested against Staphylococcus aureus, Bacillus cereus and Escherichia coli, exhibited activities with MIC values ranging from 1.25–6.25 g/mL (more active), 125–500 g/mL (moderately active), 1000–8000 g/mL (less active) and some were inactive at 16000 g/mL. The stem bark extract of Diospyros natalensis yielded two lignans namely 4-O-methylcedrusin and (-)-syringaresinol. The stem bark extract of D. squarrosa gave three compounds including methyl 2,4-dihydroxy-3,6-dimethylbenzoate, lupeol and sitostenone. The root bark methanol extract of Millettia sacleuxii yielded two pterocarpans namely (-)-medicarpin and (-)-maackiain along with 4′,7-dimethoxyisoflavone. The root bark methanol extract of Uvaria tanzaniae yielded two dihydrochalcones namely uvaretin and diuvaretin. The stem bark methanol extract of Monodora minor yielded a new indole (E)-4-(1H-indol-5-yl)-but-3-en-2-one along with sitosterol and 5-formyl-1H-indole. Uvaretin showed promising activity against Plasmodium falciparum with IC50 value of 7.20  and other compounds were inactive at 20 M concentrationExtracts which showed good activity are potential for future research.