Phytochemical investigation of harrisonia abyssinica and thespesia garckeana for antiplasmodial and antimicrobial compounds.

Abstract

Harrisonia abyssinica (Simaroubacea) and Thespesia garckeana (Malvaceae) have been used in folk medicine but there is no scientific data on them. This study therefore sought to investigate the phytochemical and microbial principles in these plants so as to improve the knowledge base and hopefully produce lead compounds. The stem bark of H. abyssinica, the roots and stems of T. garckeana were subjected to solvent extraction by cold percolation. The crude extracts underwent chromatographic separation and a total of seven compounds were isolated. The seven compounds were characterized using spectroscopic techniques and identified as obacunone (1), from H. abyssinica stem barks, gossypol (2), 6,6´-dimethoxygossypol (3), 6-methoxygossypol (4), stigmasterol (5) from T. garckeana roots, E-docosyl 3-(3,4-dihydroxyphenyl) acrylate (6) and betulinic acid (7) from T. garckeana stems. The crude extracts and all the seven compounds were tested for antiplasmodial and antimicrobial activity. The crude extract of H. abyssinica exhibited antiplasmodial activities with IC50 values of 5.6 and 4.4 µg/ml against the (D6) and (W2) strains of Plasmodium falciparum respectively. The crude extract from the roots of T. garckeana showed no antiplasmodial activity at concentrations less than 50 µg/ml, but exhibited 100 % inhibition against Candida glabrata at concentrations of 50 µg/ml. Obacunone (1) was found to have a moderate activity against D6 and W2 strains of P. falciparum with IC50 values > 4.76 µg/ml. Some compounds including gossypol (2) showed strong activity of IC50 value of 0.89 µg/ml against vancomycin resistant Enterococcus (VRE) ATCC 700221 and antimicrobial activities against Candida glabrata, Staphylococcus aureus and methicillin resistant Staphylococcus (MRS) with IC50 values of 3.21, 6.98 and 4.19 µg/ml respectively. However, its monomethoxylated derivative, 6-methoxygossypol (4) showed interesting activities against C. glabrata, MRS and vancomycin resistant Enterococcus (VRE) ATCC 51299 and ATCC 700221 strains with IC50 values of 0.8, 9.37, 2.31 and 1.45 µg/ml respectively