Ustusaustin A: a new neuraminidase inhibitory meroterpene from the ascidian-derived endophytic fungus Aspergillus ustus TK-5.

A new austin-type meroterpene, namely, ustusaustin A (1), together with seven related known analogues (2-8), were isolated and identified from the culture extract of Aspergillus ustus TK-5, an endophytic fungus obtained from the marine ascidian Pyura momus. The structures of these compounds were established on the basis of detailed interpretation of their NMR and MS data, and the relative and absolute configurations of 1 was confirmed by X-ray crystallographic analysis. Among them, ustusaustin A (1) represents the first example of 1'-nor-austin analogues with an unique 7-benzoylation. Compounds 1-4, 6, and 7 exhibited potent neuraminidase inhibitory activity and this is the first report of neuraminidase inhibitory activity for austin-type meroterpenes.