Seven new phenolic bisabolane sesquiterpenoids, (7R,10S)-7,10-epoxysydonic acid (1), (7S,10S)-7,10-epoxysydonic acid (2), (7R,11S)-7,12-epoxysydonic acid (3), (7S,11S)-7,12-epoxysydonic acid (4), 7-deoxy-7,14-didehydro-12-hydroxysydonic acid (5), (Z)-7-deoxy-7,8-didehydro-12-hydroxysydonic acid (6), and (E)-7-deoxy-7,8-didehydro-12-hydroxysydonic acid (7), along with five known analogues (8-12), were obtained from the culture of an endophytic fungus Aspergillus sp. xy02 isolated from the leaves of a Thai mangrove Xylocarpus moluccensis. All structures were assigned on the basis of detailed spectroscopic analyses. The absolute configurations of 1-4, being two pairs of epimers, were established by TDDFT-ECD calculations. Compound 12 showed mild antioxidative activity to scavenge DPPH radical with an IC50 of 72.1 μM, whereas 2, 3, 5, 7, 9, 11, and 12 displayed moderate inhibitory activities against Staphylococcus aureus ATCC 25923 with IC50 values ranging from 31.5 to 41.9 μM.
Keywords: Antibacterial activity; Aspergillus; Bisabolane sesquiterpenoids; Endophytic fungus; Mangrove.
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