VARICULANOL - STRUCTURE AND ABSOLUTE STEREOCHEMISTRY OF A NOVEL 5/12/5 TRICYCLIC SESTERTERPENOID FROM ASPERGILLUS-VARIECOLOR

The structure, absolute stereochemistry, and conformation of variculanol, a sesterterpenoid with novel skeleton isolated from Aspergillus variecolor, has been described. The molecular structure was deduced from extensive application of 2D NMR methods, in particular HMBC, which established the unambiguous assignment of the novel 5/12/5 ring system. NOEDS measurements were very useful in establishing the relative stereochemistry. The NMR-mandelate method and CD spectral analysis of the 1,17-bis(4-bromobenzoate) were used to determine the absolute stereochemistry. A unique solution-phase conformation was determined from both extensive NOE measurements and MM2 calculations and optimization.