STRUCTURE OF THE SPIROKETAL-MACROLIDE OSSAMYCIN

Ossamycin is a cytotoxic agent of undetermined structure that was orig inally isolated in 1965 from culture broths of Streptomyces hygroscopi cus var. ossamyceticus. Its overall structure and relative stereochemi stry have now been determined by single crystal X-ray diffraction stud ies. Absolute stereochemistry was established according to the previou sly determined configuration of its aminosaccharide constituent, ossam ine. The aglycone of ossamycin possesses a 24-membered macrolide ring system onto which is incorporated both a 6,6-spiroketal and a 5-member ed hemiketal ring system. The overall three-dimensional structure poss esses features in common with the related macrocyclic antibiotics duna imycin, cytovaricin, and A82548A.