8-epi-erythronolide B and its metabolic fate in fermentations of Streptomyces erythreus

8- epi -erythronolide B ( 4 ) has been isolated as a product formed from the acid treatment of erythronolide B ( 3 ). When this compound was fed to a blocked mutant of the erythromycin producing organism, Streptomycetes erythreus (Abbott 2NU153), nearly quantitative yields of 3- O -(α- l -mycarosyl)-8- epi -erythronolide B ( 10 ) were obtained. The much desired 8- epi -erythromycins ( 2 ) were not realized.