Chemophenetic significance and antibacterial activity of extract, various fractions and secondary metabolites from the stem bark of Ochna afzelii R. Br. (ex Oliv.)

Abstract

Chemical investigation of the acetone-soluble sub-fraction of the methanolic extract of the stem bark of Ochna afzelii R. Br. (ex Oliv.) led to the isolation of fourteen known secondary metabolites comprising two dimeric chalcones namely dihydrolophirone M (1) and lophirone L (2), two rearranged biflavonoids: lophirone A (3) and 4‴-methoxylophirone A (4), two biflavanone derivatives: biflavanone I (5) and biflavanone II (6), two isoflavonoids: methylirisolin (7) and biochanin A (8), one flavanol: epicatechin (9), one phenolic acid: 3,4-dihydroxybenzoic acid (10), one anthraquinone: physcion (11), two triterpenoids: lupeol (12) and oleanolic acid (13), and one steroid: sitosterol-3-O-β-d-glucopyranoside (14). Biochanin A (8) and 3,4-dihydroxybenzoic acid (10) are herein reported for the first time from the family Ochnaceae. The antibacterial activity was assessed in vitro against pathogenic strains of Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis. The crude methanolic extract as well as its acetone-soluble and insoluble fractions exhibited high to significant antibacterial activity, while isolated compounds mostly displayed moderate antibacterial activity (MIC = 16–64 μg/mL).