ISOLATION AND STRUCTURAL ELUCIDATION OF SECONDARY METABOLITE FROM STEM BARK EXTRACT OF Pterocarpus Mildbreadii

Abstract

Pterocarpus mildbreadii leaves and stem bark have been exploited in Nigeria, in the area of alternative medicine, due to their numerous biological properties. The upsurge in the search for new chemical agents to replace conventional drugs, prompted this study. The study was carried out for the first time, in the area of isolation and structural elucidation of bioactive compounds, from the ethanolic extracts of the stem bark of Pterocarpus mildbreadii. The ethanol extract of the stem bark was separated using column chromatographic technique. The fractions obtained were screened for antioxidant activity in a DPPH assay. The active fraction was further purified and the structure elucidated by subjecting it to a number of identification instruments, such as FTIR, MS and 1D &2D NMR spectroscopy. The FTIR analysis of isolated bioactive compound gave the following λ max: 3400-2500 cm-1 a broad band characteristic of a carboxylic acid functional group and 1740 cm-1 carbonyl stretch. The mass spectrum game a molecular ion peak at m/z 282 consistent with the molecular formula C18H34O2. The proton NMR showed a doublet of doublet of doublet at 4.9, 5.3 and 5.8 ppm attributed to vinyl protons, two proton multiplets at 1.6,1.3, and 1.2 ppm; and a three proton triplet at 0.9 ppm. The HMBC and 13C NMR showed the presence of a carboxylic carbon at 176 ppm and vinylic carbons at 135 and 143 ppm respectively; the methyl carbon was observed at 14.12 ppm. On the basis of spectral analysis, results obtained suggested compound was cis-vaccenic acid and was confirmed by comparison with literature data. Isolated compound has antioxidant activity, with a maximum percentage scavenging activity of 89.66. The present study lends credence to the use of the plant in traditional medicine and posits pterocarpus mildbreadii as a rich source of secondary metabolites which can find application in the pharmaceutical industries.