Biological activities of benzoquinones from Badula barthesia and Embelia angustifolia

In our screening program for antihypertensive plant constituents extracts of the leaves and bark of Badula barthesia showed strong in vitro inhibition of angiotensin converting enzyme (ACE). Rapanone (1), 2,5-dihydroxy-3-tridecyl-1,4-benzoquinone, was isolated as an active constituent of the leaves. The IC(50) values of rapanone and three 3-alkyl-2,5-dihydroxybenzoquinones, (2)-(4), (Z)-2,5-dihydroxy-3-(pentadec-8-enyl)-1,4-benzoquinone, (Z,Z)-2,5-dihydroxy-3-(heptadeca-8,11-dienyl)-1,4-benzoqui-none and (Z)-2,5-dihydroxy-3-(heptadec-8-enyl)-1,4-benzoquinone recently isolated from Embelia angustifolia were determined. The following IC(50) ± S.D. values have been obtained (1) 36 ± 4.6 μM, (2) 19 ± 6.2 μM, (3) 19 ± 8.7 μM and (4) 16 ± 3.0 μ.M. The IC(50) value for the reference compound Captopril was determined to 12 ± 2.6 nM. The antimicrobial activity of the four compounds was determined by thin layer chromatography agar overlay technique as minimum growth inhibitory amount in μg. One yeast, Candida albicans, and four bacteria, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus were used as test organisms.