Secondary Metabolites from Annulohypoxylon sp. and Structural Revision of Emericellins A and B.

Seven previously undescribed compounds were isolated from the endophytic fungus Annulohypoxylon sp. KYG-19 (family Xylariaceae), including three gymnomitrane-type sesquiterpenes xylariacinols A, B, and D ( 1 , 2 , and 4 ), one bisabolane-type sesquiterpene annulnol F ( 6 ), one phenol derivative lariacinol G ( 7 ), and two polyhydroxy compounds hypoxylonols H and I ( 8 and 9 ), together with two known gymnomitrane-type sesquiterpenes emericellin A ( 3 ) and 3-gymnomitren-15-ol ( 5 ). The assignments of their structures was determined by extensive spectroscopic and spectrometric analysis, acetonide analysis, Mosher's method, and X-ray crystallography. In addition, the structures of emericellins A and B, which were reported to possess an unprecedented tricyclo[4, 4, 2, 1]hendecane scaffold, were revised by comparing their spectroscopic data with those of 1 and 3 . Compounds 1 and 4 exhibited antibacterial activity against Escherichia coli with minimum inhibitory concentrations of 4 and 2 μg/mL, respectively.