Nigerapyrones A-H, α-pyrone derivatives from the marine mangrove-derived endophytic fungus Aspergillus niger MA-132

Eight new α-pyrone derivatives, namely, nigerapyrones A-E (1-5) and nigerapyrones F-H (8-10), along with two known congeners, asnipyrones B (6) and A (7), were isolated from Aspergillus niger MA-132, an endophytic fungus obtained from the fresh tissue of the marine mangrove plant Avicennia marina. The structures of these compounds were elucidated on the basis of spectroscopic analysis. The undescribed geometries of the trisubstituted double bonds (C-9 and C-11) for asnipyrone B (6) have now been explicitly determined, while the incorrect placement of the methyl group at C-5 of asnipyrone A (7) has now been revised at C-3. The cytotoxic activities of the isolated α-pyrone derivatives against eight tumor cell lines as well as antimicrobial activities against two bacteria and four plant-pathogenic fungi of these compounds were evaluated. Compounds 2, 4, 5, and 7 showed weak cytotoxicity against some of the tested tumor cell lines.