Structure and stereochemistry of multicolanic, multicolic, and multicolosic acids, 4-ylidenetetronic acid metabolites from Penicillium multicolor. Synthesis of methyl (E)-O-methylmulticolanate
Abstract
The application of 2-methoxy-3-n-pentylmaleic anhydride (8) in the synthesis of methyl O-methylmulticolanate (9) and its geometrical isomer is described. Comparison of 1H and 13C n.m.r. data with those of the dimethyl derivative of natural multicolanic acid (1a) from Penicillium multicolor establishes an E-geometry for (1a), and for the related multicolic (1b) and multicolosic acids (1c). The alternative bis-butenolide formulation (11) is entertained for the ylidenetetronic acids.