Synthesis of (+)-8-methyl cercosporamide: Stereochemical correlation of natural (-)-cercosporamide with (+)-usnic acid

Article abstract of DOI:10.1016/S0040-4020(01)81572-6

The absolute configuration of the antifungal antibiotic cercosporamide was established as C-9b-(-)-(S) by correlation with synthetic (+)-8-methylcercosporamide. This was accomplished via conversion of the isoxazole (6) available from (+)-usnic acid. Structure revision of the key isoxazole (6), previously assigned structure (5), is described; some of the ¹³C-assignments for usnic acid made by previous workers have also been corrected.