Antifungal diastereomeric furanones from Mutisia friesiana: structural determination and conformational analysis

Two diastereomeric furanones, (4S.5S)-5-(4'-methyl-3'-pentenyl)-4-hydroxy a nd (4S,5R)5-(4'-methyl-3'-pentenyl)-4-hydroxy-5-methyldihydrofuran-2-one 2 were isolated for the first time from the shrub Mutisia friesiana, The rela tive stereochemistries of 1 and 2 were ascertained from NOESY NMR dat;l and confirmed by a combination of molecular modeling (molecular mechanics and ab initio molecular orbital calculations) and NMR data. Comparison between experimental and calculated H-1-H-1 vicinal coupling constants revealed tha t both furanones exist in an equilibrium of two stable conformers of the fi ve-membered ring. Application of Mosher's method suggests that both diaster eomeric furanones have the same (S)-configuration at C-(4) and are epimers at C-(5). Furanones 1 and 2 showed antifungal activity against the pathogen ic fungus Cladosporium cucumerinum. (C) 2001 Elsevier Science Ltd. All righ ts reserved.