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

A new austin-type meroterpene, namely, ustusaustin A (), together with seven related known analogues (-), were isolated and identified from the culture extract of TK-5, an endophytic fungus obtained from the marine ascidian . 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 was confirmed by X-ray crystallographic analysis. Among them, ustusaustin A () represents the first example of 1'-nor-austin analogues with an unique 7-benzoylation. Compounds -, , and exhibited potent neuraminidase inhibitory activity and this is the first report of neuraminidase inhibitory activity for austin-type meroterpenes.