Microbial metabolites. Part XI. Total synthesis and absolute configuration of (S)-carlosic acid (4-butyryl-2,5-dihydro-3-hydroxy-5-oxo-furan-2-acetic acid) and conversion of (R)-5-methyltetronic acid into (R)-carolic acid {3,4-dihydro-8-methylfuro[3,4-b]oxepin-5,6(2H,8H)-di-one}

Abstract

Syntheses of (S)-2,5-dihydro-3-hydroxy-5-oxofuran-2-acetic acid (5) and its methyl ester are described. Biomimetic acylations of the ester and of (R)-3-hydroxy-2-methylfuran-2(5H)-one[(R)-γ-methyltetronic acid](1) to produce (S)-carlosic acid (3) and (R)-carolic acid (2), respectively, are described. The absolute configuration of carlosic acid from Penicillium charlesii NRRL 1887 has been established as S.