Antimicrobial prenylated acetophenones from berries of Harrisonia abyssinica

The ripe berries of Harrisonia abyssinica yielded two new prenylated acetophenones, namely 5-(ethan-1'''-one)-4,6-dihydroxy-7-(3'',3''-dimethylallyl)-2 S-(1' S-hydroxy-1',5'-dimethylhex-4'-enyl)-2,3-dihydrobenzofuran (1) and 5-(2'''-hydroxyethan-1'''-one)-4,6-dihydroxy-7-(3'',3''-dimethylallyl)-2 S-(1' S-hydroxy-1',5'-dimethylhex-4'-enyl)-2,3-dihydrobenzofuran (2), herein named harronin I and harronin II, respectively. The compounds were isolated following activity guided fractionation and the structures were determined using 1D, 2D NMR spectroscopic, CD and MS spectrometric techniques. The methanol-dichloromethane mixture (1 : 1 v/v) crude extract exhibited strong antimicrobial activity against Candida albicans, Bacillus cereus, Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, and Lactobacillus casei. Harronin I (1) showed a MIC of 5 µg/mL against C. albicans, 6 µg/mL against B. cereus, and more than 20 µg/mL against other tested microorganisms. Harronin II (2) showed much weaker MIC values (> 100 µg/mL) against all the tested microorganisms.