In vitro antimicrobial activities guided isolation of novel compounds from selected fractions of three South African Hypoxis species

Introduction This study demonstrated the quest to fully expound the phytochemical composition of some South African medicinal Hypoxis species including H. hemerocallidea, H. colchicifolia and H. galpinii. Methods In vitro minimum inhibitory (MIC) studies of extracts (ethanol, acetone, ethyl acetate and chloroform) of these three species were investigated against staphylococcus aureus, Enterococcus faecalis , Bacillus cereus, Escherichia coli, and Candida albicans . Vacuum liquid and column chromatography were used for the isolation of compounds from extracts with the best antimicrobial potentials. Results The chloroform extract of H. colchicifolia exhibited best in vitro MIC of between 2.0 and 0.25 mg mL⁻¹ against all the pathogens while the ethyl acetate fraction of H. galpinii exhibited poorest minimum inhibitory concentration (MIC) of 4.0 and 8.0 mg mL⁻¹ for the same pathogens. Based on the in vitro antimicrobial inhibition by the extracts (chloroform ' acetone ' ethanol ' ethyl acetate), two new phenolic glycosides named hemerocalloside and colchicoside were isolated from acetone fraction of H. hemerocallidea and ethanol fraction of H. colchicifolia respectively . In addition, known curculigoside C (from ethanol fraction of H. colchicifolia), oleic acid and 2-hydroxyethyl linoleate (from chloroform fraction of H. hemerocallidea) were also isolated. All the structures were elucidated based on IR, UPLC-MS, GC-MS, 1D and 2D NMR. Conclusions Hypoxoside and β-sitosterol are not the only active secondary metabolites in Hypoxis hemerocallidea and related species and the two new glycosides, hemerocalloside and colchicoside underpins the novelty and vital outcome of this study.