Chemical constituents and bioactivity studies of bauhinia rufescens lam. (fabaceae) and ficus platyphylla del. (moraceae)

Abstract

The chemical constituents and bioactivities of the stem barks and leaves of Bauhinia rufescens and the stem barks of Ficus platyphylla have been studied. Extraction of the plant materials using Soxhlet method with petroleum ether, ethyl acetate, and methanol afforded nine crude extracts. Fractionation and purification of the ethyl acetate and methanol extracts of stem bark of B. rufescens yielded two new compounds identified as 4-(2'-hydroxyphenethyl)-5-methoxy-2-methylphenol and bauhiniside. Compounds identified as 6-methoxy-7-methyl-8-hydroxydibenz [b,f]oxepin, a-amyrin acetate, ß-sitosterol 3-O-ß-D-xylopyranoside, menisdaurin, sequoyitol, 6-hydroxy-7,7a-dihydrobenzofuran-2(6H)-one, glyceryl trilinoleate, linoleic acid, stigmasterol and ß-sitosterol were also isolated from the stem barks. The leaves extract yielded glyceryl trilinoleate, sequoyitol and bauhiniside. F. platyphylla yielded two new phenolic compounds from its methanolic extract which was identified as ficuside A and ficuside B. In addition, hordenine was isolated via alkaloid extraction, and also 3,4-dihydroxybenzoic acid anhydride, epicatechin, lupeol, lupeol acetate and a-amyrin acetate were identified from F. platyphylla. Bioactivities including antioxidant, antimicrobial, inhibitory studies on the brine shrimp larvae, tyrosinase, acetylcholinesterase and cyclooxygenase-2 were investigated. Among the nine crude extracts from the two plants, the methanol extract from the stem barks of B. rufescens showed a strong DPPH radical scavenging activity (14.31 µg/mL), and similar extract from F. platyphylla showed higher total phenolic content (719.58 µg GAE/mg), while the methanol extract from the leaves of B. rufescens showed the highest antioxidant value based on ß-carotene bleaching assay (78.75%). The antimicrobial activity revealed the methanol extract from F. platyphylla was active against Gram-positive bacteria, Staphylococcus aureus (113 µg/mL) and a fungus, Aspergillus niger (56 µg/mL). Meanwhile, toxicity study indicated that, ethyl acetate from the leaves of B. rufescens was toxic against brine shrimp larvae (LC50 0.06 mg/mL). The methanol extract from F. platyphylla was found active against tyrosinase enzyme (49.2%). Evaluation of acetylcholinesterase inhibition using the microplate and bioautographic assays showed the methanol extract from F. platyphylla inhibited the enzyme activity with percent inhibition of 44.7% (LD 30.0 µg). In addition, among the isolated compounds, oxepin from the stem barks of B. rufescens was found to be active against Staphylococcus aureus (113 µg/mL) and lupeol acetate from F. platyphylla was found active against Candida glabrata (56 µg/mL). It was also found that, hordenine inhibited acetylcholinesterase activity at 58.6% (LD 33.0 µg). Lupeol and 3,4-dihydroxybenzoic acid anhydride from F. platyphylla showed the highest inhibitory activity against tyrosinase (67.7%) and COX-2 (IC50 0.15 µM) enzymes, respectively.