Antibacterial thymol derivatives isolated from Centipeda minima

Two new monoterpenoids, 8,10-dihydroxy-9(2)-methylbutyryloxythymol (1) and 10-hydroxy-8,9-dioxyisopropylidene-thymol (2), together with five known thymol derivatives: 8,9,10-trihydroxythymol (3), thymol-beta-glucopyranoside (4), 9-hydroxythymol (5), 8,10-dihydroxy-9-isobutyryloxythymol (6), and 8-hydroxy-9,10-diisobutyryloxythymol (7), were isolated from Centipeda minima. Their structures were identified by means of spectroscopic analyses. Interestingly, compound 2 is not an extraction artifact according to a close HPLC examination of material after extraction by analytical MeOH at ambient temperature. The antibacterial activities of compounds 1-7 were evaluated against eight microbial strains by the agar dilution method.