Recently we have found a novel antifungal substance possessing growth self-inhibiting activity from cherry brown rot fungus M. fructicola, which was named chloromonilicin (1). 1 was isolated from the culture filtrate of this fungus, and its novel structure with β-chloro-α,β,γ,δ-unsaturated seven-membered lactone ring was determined on the basis of chemical and spectroscopic evidence. In addition, a new xanthone metabolite obtained was identified as 4-chloropinselin (7), suggesting 7 to be a probable precursor of 1. These bromine congeners, bromo-monilicin (8) and 4-bromopinselin (9), were prepared for biological activity and biosynthetic studies by inoculation of M. fructicola into a KBr-containing medium. Antimicrobial activity of 8 was about one-fourth of that of 1. Biosynthetic incorporation of 9 into 8 was accomplished. To the best of our knowledge, this is the first instance of Baeyer-Villiger type oxidation of phenolic metabolites. In addition to 8 and 9, a new benzophenone derivative, which was named moniliphenone, was isolated and identified as 12. Deuterated 12's were prepared by treatment of 12 with methanol-d_4 in the presence of catalytic amount of sulfuric acid and was shown to be straightforwardly incorporated into 7 and 1. Furthermore, an anthraquinone pigment, chrysophanol, was isolated as a probable precursor of 12. These observations show that the biosynthesis of 1 in M. fructicola proceeded in the sequence chrysophanol (13)→12→7→1.
