Abstract The aim of this study was to isolate and evaluate the antimicrobial constituent of the leaves of Pterocarpus santalinoides DC (Fabaceae) growing in the tropical rain forest region of Nigeria, Sub Saharan Africa. The powdered leaf materials were defatted with n-hexane and extracted in a soxhlet extractor with 90.0 % methanol. The methanol extract was further fractionated to yield the chloroform, ethyl acetate, butanol and methanol soluble fractions. Each of the fractions was screened for antimicrobial activity using Agar-well diffusion method. Phytochemical tests were carried out using standard procedures. The fractions that had antimicrobial activity were subjected to column chromatographic separation and monitored by analytical thin layer chromatography (TLC). The n-butanol fraction that gave the best antimicrobial bioassay result was subjected to further fractionation and purification to afford some pooled fractions.FractionF5 that showed good antimicrobial activity was subjected to semi-preparative chromatographic purification to isolate the bioactive constituent. The isolate was characterized using a combination of analytical and spectral techniques which included: ultra violet (UV), Fourier Transform Infrared spectrometry (FTIR), gas chromatography-mass spectroscopy (GC-MS), etc.
Preliminary phytochemical screening showed that the leaves of Pterocarpus santalinoides contained alkaloids, tannins, flavanoids, saponins, terpenoids and free anthraquinones. All fractions tested showed mild antimicrobial activity. The Infrared (IR) chromatogram revealed peaks that strongly suggest the presence of O-H, C-H, RC=C-H, C=O and C=N functional groups. These preliminary results indicated that the antimicrobial potential of leaves of Pterocarpus santalinoides may be attributable to such hydroxyl (OH)-bearing constituents like alkaloids, tannins, saponins, terpenoids, flavanoids and anthraquinones which might be responsible for this activity either singly or in combinations. Other analytical and phytochemical parameters are being evaluated to elucidate the actual structure of the active ingredient.
Keywords Antimicrobial, Pterocarpus santalinoides, Phytochemical, Fourier Transform Infrared Spectrometry.