Phytochemical and anti-microbial investigation of ochna holtzii gilg. from the Kenyan Costal region
Awadh, Mohamed Mbarak
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Plants are used widely in traditional health systems to treat a variety of diseases. This research was specifically directed to investigate a coastal plant Ochna holtzii Gilg., a medicinal plant mainly found in the coastal region of Kenya. The communities in the region use various parts of the plant (stem and root bark) to treat different health problems. Common uses include treatment of high fever, headache and coughs, and relieving persistent backaches especially in the old age. It is also used extensively as a mixture with other plant extracts in treating microbial infections. Crude solvent (hexane, DCM, ethyl acetate and methanol) extracts of O. holtzii were subjected to antimicrobial bioassays against two Gram-positive bacteria: Staphylococcus aureus and Bacillus subtilis, two Gram-negative bacteria: Salmonella typhi and Pseudomonas aeruginosa and a yeast Candida albicans. The methanol extracts of the root bark (2 mg/disc) showed the highest activity against B. subtilis and S. aureus with zones of inhibition of 20 and 14 mm, respectively. The zones of inhibition for the stem bark against the same bacteria were 14 and 12 mm, respectively. Ethyl acetate extracts of both the root and the stem bark (2 mg/disc) showed moderate activities against the same bacteria with zones of inhibition of 11 and 9 mm, respectively. Hexane and DCM extracts showed no activity. The minimum inhibitory concentrations (MICs) of the root bark methanol extract was 250 and 500 ug/ml against B. subtilis and S. aureus, while that of the stem bark was 500 and 1000 ug/ml, respectively. Isolation and purification of the bioactive constituents of the plant were made using standard chromatographic techniques: VLC, TLC, CC, prepTLC, Sephadex LH-20. Eight compounds were isolated in relatively pure forms from ethyl acetate extracts of root and stem barks. The structures of the compounds were elucidated using standard spectroscopic techniques: UV, IR, 1 D and 2D NMR and comparison with known spectral data. All compounds except one were found to be rearranged biflavonoids, of which three [afzelone D methylether (MM/HRE/03), dehydrolophirone C (MM/HSE/04) and the dephenyl lophirone C (MM/HSE/06)] have not been reported previously, while the other four [lophirone A (MM/HRE/01), afzelone D (MM/HSEV/02), lophirone K (MM/HSE/05) and calodenin B (MM/HRE/07)] are known compounds. The eighth compound was 5-methyl-3,5-resorcinol (MM/HSE/08). Three of the compounds: lophirone A, afzelone D methylether and calodenin B were isolated from the root bark. Two compounds (lophirone A and calodenin B) were bioassayed against S. aureus and P. aeruginosa where lophirone A showed significant activity with zone of inhibition 15 and 11 mm, respectively. Calodenin B was less active against the same bacteria, with zones of inhibition of 11 and 13 mm, respectively. Further extensive research work needs be done on the isolation and identification of other constituents of the plant to establish the full range of bioactive constituents in O. holtzii.