SECONDARY MOLD METABOLITES .41. STRUCTURE AND BIOSYNTHESIS OF CERCOSPORA-BETICOLA TOXIN (CBT)

The structure of Cercospora beticola toxin (CBT) 1, a phytotoxic metabolite, was elucidated on the basis of mass, H-1 NMR, C-13 NMR and 2D NMR (C-13, C-13 COSY and H-1, H-1 ROESY) spectra and from biosynthetic evidence obtained from incorporation of [1-C-13]acetate and (1,2-C-13]acetate. The product is a 2:2 complex with Mg of a compound derived from the coupling of two octaketide-derived reduced anthraquinone and xanthone moieties.