HPLC purification of destruxins produced by Alternaria brassicae in culture and leaves of Brassica napus

Abstract

Reversed-phase chromatography was applied for preparative isolation of destruxins from the plant pathogenic fungus Alternaria brassicae. Sample preparation on Sep-Pak C18 cartridges followed by HPLC allowed preparative isolation of two major phytotoxins, destruxin B and homodestruxin B, from the culture broth of the fungus, and also minor quantities of destruxin B, not previously reported. Additionally, identification of the two major toxins was, for the first time, made in leaf tissue infected by the fungus. Destruxin B and homodestruxin B were identified by their 1H and 13C NMR spectra, which were assigned by homonuclear and heteronuclear 2D NMR techniques. Based on this, the minor components were identified as destruxin B2 by homonuclear ID and 2D NMR. The proposed structure was confirmed by FAB/SIMS.