The biosynthesis of fungal metabolites. Part III. Structure of shamixanthone and tajixanthone, metabolites of Aspergillus variecolor

The structures of shamixanthone and tajixanthone, optically active metabolites of Aspergillus variecolor, are shown to be (1R,2S)-1,11-dihydroxy-2-isopropenyl-5-methyl-8-(3-methylbut-2-enyl)-(IV) and (1R,2S)-8-[(2S)-2,3-epoxy-3-methylbutyl]-1,11-dihydroxy-2-isopropenyl-5-methyl-2,3-dihydro-1H-pyrano[3,2-a]xanthen-12-one (V) respectively. These structures were established by detailed analyses of the 1H and 13C n.m.r. spectra of the metabolites and their derived compounds as well as by chemical degradation of the substituted dihydrobenzopyran system. The absolute configurations were assigned by application of the Horeau asymmetric synthesis.