Antimicrobial, antioxidant and cytotoxicity of isolated compounds from leaves of Pappea capensis

Pappea capensis is a medicinal plant widely used in the management of eye infections, sexually transmitted infections and as an aphrodisiac in South Africa. Two flavonoids quercetin-3-O-rhamnoside (1) and epicatechin (2) were isolated through bio-assay guided fractionation. The extracts and isolated compounds were evaluated for antimicrobial, antigonococcal, antioxidant and cytotoxicity potential. The ethyl acetate fraction exhibited a broad spectrum of activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Candida albicans with MIC values ranging from 0.39 to 0.78 mg/mL. In the DPPH radical scavenging assay, extracts and isolated compounds showed free radical scavenging activity with EC50 values ranging from 6.34 to 158.00 μg/mL. The isolated compound epicatechin (2) exhibited higher antioxidant activity in the β-carotene-linoleic acid model system (EC50 = 9.64 μg/mL) than the ascorbic acid standard (EC50 = 13.37 μg/mL). Cytotoxicity of the samples was determined using the MTT (3-(4,5-dimethylthiazol)-2,5-diphenyl tetrazolium bromide) assay against Vero monkey kidney cells. Little to no cytotoxicity of the extracts and isolated compounds was observed. These results may help to discover new chemical classes of natural antimicrobial and antioxidant substances that could serve as selective agents for infectious microbial diseases.