PHYTOCHEMICAL AND BIOLOGICAL STUDIES OF THE COMPOUNDS FROM THE ROOT BARK OF VERNONIA AURICULIFERA; HIERN (ASTERACEAE)

Abstract

In the present study, the root bark of V. auriculifera was sequentially extracted with n-hexane, dichloromethane (DCM) and methanol respectively. The activities of crude extracts of n-hexane, DCM and methanol against brine shrimp larvae were compared. As larvicides, the DCM crude extract was most active (LD50 = 318 ppm), followed by n- hexane (LD50 = 788 ppm), and lastly by methanol extract (LD50 = 931 ppm). The anti-bacterial assay showed that crude extracts were generally more active on E. coli than S. aureus. n-hexane and methanol extracts were found to be active against E. coli (Inhibition diameter > 10 mm) at 1000 ppm. Fractionation of DCM extracts appears to have yielded compounds whose activity against S. aureus seems to be enhanced. Fractionation is thought to concentrate active ingredients. The n-hexane extract, methanol extract and compounds 3, 4, 5, 10 and 11 with activities (inhibition diameters ≥ 10 mm) against E. coli can be used to control this bacterium. For S. aureus only compounds 5, 7, 9 and 10 which had activities ≥ 10 mm that could be used to control it. The fungal assay using Candida albicans showed significant activity (Inhibition diameter > 10 mm) with n–hexane and DCM extracts. For compounds only 1 and 11 had good 16 results (inhibition diameters ≥ 10) with this fungus. Thus n-hexane, DCM extracts and compounds 1 and 11 could suitable candidates for control of Candida albicans. Column chromatography of the n-hexane extracts followed by re-crystallization in methanol yielded two triterpenoids which were characterized as lupeol (6) and an ester of a long chain fatty acid and taraxerol (7) whose suggested name is α-taraxerol octanoate and is a possible novel compound. The structures of these compounds were elucidated and using ¹H-NMR and ¹³C-NMR experiments and also matching their spectra with those found in the literature. Melting points, ultra-violet (UV) and infra-red (IR) absorptions of these compounds are reported.