Bioactive compounds from the leaf extract of Bauhinia galpinii (Fabaceae) used as antidiarrhoeal therapy in southern Africa

Abstract Bauhinia galpinii N. E. Br is a shrub or small tree that grows 3–9 m tall throughout South Africa in nature and as ornamental plant. Various parts of the plant are used to cure gastrointestinal tract (GIT) disorders, epilepsy, convulsion, infertility, and amenorrhoea. Despite popular use, the phytochemicals responsible for the medicinal efficacy of the plant has not been exhaustively investigated. Bioautography-guided fractionation was used to isolate the antimicrobial phytochemicals of the acidified 70% acetone leaf extract. A combination of open column chromatography using silica gel 60, Sephadex LH-20, normal phase thin-layer chromatography (TLC) on precoated Kieselgel 60F 254 plates and the spots visualized under UV 366 and UV 254 light, and spray reagents (vanillin/sulphuric acid) were used to isolate compounds. The compounds were identified by UV spectra, extensive 1D and 2D NMR spectroscopy, mass spectrometry and comparison of the data with those reported in the literature. The antimicrobial activity of isolated compounds was determined against Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 29213), Enterococcus faecalis (ATCC 29212), Candida albicans (ATCC 10231), clinical isolates of Cryptococcus neoformans , Aspergillus fumigatus , C. albicans (M0824), C. albicans (M0825), C. albicans (1051604),and C. albicans (1051608) using a serial dilution microplate method. Result : Six compounds including two novel (24-Isopropylcholest-5-en-3,8-diol( 1 ) and 5, 7, 4′ 5′ tetrahydroxy-2′-methoxyflavone (isoetin 2′ methyl ether) ( 4 )) and four known (3, 5, 7, 3′, 4′-pentahydroxyflavone (quercetin) ( 2 ); 3, 5, 7, 3′, 4′, 5′-hexahydroxyflavone (myricetin) ( 3 ); quercetin-3-O-β-galactopyranoside ( 5 ) and myricetin-3-O-β-galactopyranoside ( 6 )) were isolated and characterised. The isolated compounds inhibited antimicrobial growth with MICs ranging between 3.9 and 125 μg/. The results may provide a rational support for the traditional use of Bauhinia galpinii leaf in the treatment of infectious gastrointestinal disorders, since antimicrobial compounds especially the flavonoids isolated from the 70% acetone extract may also present in the traditional water extract. They could be responsible for the broad spectrum of antimicrobial activity of B. galpinii extract.