Pigments of Fungi. LXIII. Synthesis of (1S,3R)- and (1R,3S)-Austrocortilutein and the Enantiomeric Purity of Austrocortilutein in some Australian Dermocybe Toadstools

Abstract

The naturally occurring tetrahydroanthraquinones (1S,3R)- and (1R,3S)-austrocortilutein (1b) and (1d), respectively, are synthesized for the first time in enantiomerically pure form by Diels–Alder cycloaddition between the functionalized butadiene derivative (4) and the corresponding monochiral trans-1,3-dihydroxy-1,2,3,4- tetrahydro-5,8-naphthoquinone (5a) or (5b), themselves derived from citramalic acid. Separation of the four stereoisomeric austrocortiluteins by using h.p.l.c. over a chiral stationary phase reveals that the enantiomeric purity of the (1S,3S)- and (1R,3R)-quinones (1a) and (1c) varies from species to species whereas the (1S,3R)-isomer (1b) is, in the five cases examined, enantiomerically pure.