Ukulactones A and B, new NADH-fumarate reductase inhibitors produced by Penicillium sp. FKI-3389

Screening for NADH-fumarate reductase inhibitors led to the isolation of the new polyketide compounds, ukulactones A and B (1 and 2, Fig. 1) from a culture broth of Penicillium sp. FKI-3389. The structure of ukulactone A was elucidated as a methylated derivative of prugosene A1, which was produced by Penicillium rugulosum and NOESY experiment revealed ukulactone B was a stereoisomer of ukulactone A. Ukulactone A showed potent inhibitory activity against NADH-fumarate reductase of the roundworm Ascaris suum in vitro.