The antibacterial, antioxidant and sun protection potential of a benzophenone from Dolichopentas decora (S. Moore)

Abstract

Dolichopentas decora (S.Moore) (Rubiaceae) is used locally in Western Uganda in the treatment of microbial skin infections and could therefore be a potential source of antimicrobial agents. This study aimed at the isolation and identification of compounds from D. decora leaf extracts and an investigation of their bioactivities. The compounds were sequentially extracted from the powdered aerial plant parts using n-hexane, EtOAc, MeOH, and distilled water, and compounds were isolated using a combination of chromatographic techniques. Structure elucidation was performed using NMR spectroscopy and mass spectrometric techniques. This resulted in the identification of seven known compounds: squalene (1), β-sitosterol (2), stigmasterol (3), ursolic acid (4), rutin (5), mitraphenone A (6), and protocatechuic acid (7). An investigation of the antibacterial activity of the extracts and isolated compounds was carried out using an agar well diffusion test against Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae. In addition, the extracts and isolated compounds were screened for antioxidant activity using the 2,2-diphenyl-1-picryl-hydrazyl (DPPH) radical scavenging assay. Compound (6) was screened for sun protection potential between 290 and 320 nm. The binding interactions of compound 6 against the penicillin-binding protein 1b (PBP 1b) of E. coli were studied using Molecular Operating Environment (MOE) 2015.10 software. Compound 6 was found to be active against K. pneumoniae (zone of inhibition, 10.0 ± 0.1 mm), it showed a good sun protection factor (SPF = 24.61) and a low radical scavenging activity (28.8 %). Compound 6 binds better to lysine through the hydroxyl group of C-6’’ with a binding affinity value (ΔG = − 3.7 kcal/mol). This study is the first report of compounds 1–7 from D. decora.