Metabolites produced by the scleroderris canker fungus, Gremmeniellaabietina. Part 2. The structure of scleroderolide

Abstract

Scleroderolide, a yellow pigment produced by the Scleroderris canker fungus Gremmeniellaabietina (Lagerb.) Morelet, is shown to possess structure 1. The structure was determined by an X-ray crystallographic study of the racemic monoacetate 1a. The crystal of 1a belongs to the triclinic system space group, P1, the R-factor converged to 0.047 for the 1957 observed reflections. Scleroderolide occurs mainly as the levorotatory enantiomer (S configuration at C-2′) although on one occasion it was obtained in partially racemic form. The absolute stereochemistry of the levorotatory form was determined by transformation of (−)-sclerodione (5) of known absolute configuration into (−)-scleroderolide. The absolute configuration of (−)-sclerodione was established by correlation with (−)-sclerodin (3). The diacetyl derivative of scleroderolide (1b) shows interesting temperature dependent nuclear magnetic resonance spectral properties due to restricted rotation of the C-4 O-acetyl group. Oxidation of the red pigment sclerodione (5) with m-chloroperbenzoic acid provides both sclerodin (3) and scleroderolide (1). Scleroderolide (1) is the first natural product to be reported that contains a phenylglyoxylate lactone functionality.