STRUCTURE AND BIOSYNTHESIS OF XANTHOQUINODINS, ANTICOCCIDIAL ANTIBIOTICS

The structures of xanthoquinodins A1, A2, A3, B1, and B2, anticoccidial antibiotics, produced by Humicola sp. FO-888 were confirmed by analyzing C-13-labeled xanthoquinodins prepared biosynthetically in C-13-labeled precursor feeding experiments on the basis of extensive spectroscopic techniques including H-1-H-1 COSY, C-13-H-1 COSY, and HMBC. Xanthoquinodins are the first heterodimers of octaketide-derived xanthone and anthraquinone monomers connected in an ''end-to-body'' fashion. The stereochemistry of xanthoquinodin B2 was determined by NMR including NOE measurements. Accordingly, the stereochemistry of xanthoquinodins A1, A2, and B1 was also deduced by studying the mechanism of interconversion among xanthoquinodins.