Pigments of fungi, part 19. A degradative method for the determination of central chirality in naturally occurring 3-hydroxy-3-methyl-3,4-dihydroanthracen-1(2 H)-ones: Application to pigments of the flavomannin type.

Abstract

The absolute stereochemistry at both chiral centres in the flavomannin-6,6′-di- O-methyl ethers A 1 ( 23) and B 1 ( 24) si determined as ( R) by chemical correlation over six steps without the need for intermediate purification with methyl ( S)-(−)-tetrahydro-2-methyl-5-oxo-2-furanetate ( 25); the methodology is developed using the fungal metabolite ( S)-torosachrysone ( 2) as an initial substrate.