New Terpendole Congeners, Inhibitors of Sterol O-Acyltransferase, Produced by Volutella citrinella BF-0440.

New terpendoles N-P (1-3) were isolated along with 8 structurally related known compounds including terpendoles and voluhemins from a culture broth of the fungus Volutella citrinella BF-0440. The structures of 1-3 were elucidated using various spectroscopic experiments including 1D- and 2D-NMR. All compounds 1-3 contained a common indole-diterpene backbone. Compounds 2 and 3 had 7 and 6 consecutive ring systems with an indole ring, respectively, whereas 1 had a unique indolinone plus 4 consecutive ring system. Compounds 2 and 3 inhibited both sterol O-acyltransferase 1 and 2 isozymes, but 1 lost the inhibitory activity. Structure-activity relationships of fungal indole-diterpene compounds are discussed.