Secondary mould metabolites. Part 36. Isolation and structure elucidation of sulcatines C–E, novel norsesquiterpenes from Laurilia sulcata, and 7-epi-sulcatine D

Abstract

Three novel norsesquiterpenes, sulcatines C–E (5, 6 and 11), have been isolated from still liquid cultures of Laurilia sulcata. Their structures were elucidated by ¹H and ¹³C NMR spectroscopic studies, including ¹H–¹³C heteronuclear correlation spectra (HETCOR and COLOC), and the relative configurations were established through a series of NOE difference spectra and the magnitude of the ¹H–¹H coupling constants. The absolute configuration of these metabolites was deduced by the application of the exciton chirality method to the pivalate dibenzoate of sulcatine D, compound 9. Sulcatines C and E (5 and 11) were shown to exist in solution as an equilibrating mixture of ring-closed hemiketal (5a and 11b) and ring-opened keto (5c and 11a) forms. By reduction with NaBH₄ sulcatine C 5 afforded a separable mixture of sulcatine D 6 and its C–7 epimer 10.