Base-catalyzed isomerism in elfamycin antibiotics. Structures of ganefromycins epsilon and epsilon 1

The structures of ganefromycins epsilon (2a) and epsilon 1 (2b) have been determined by spectroscopic techniques. The compounds are isomeric deoxygenated precursors of the parent antibiotics ganefromycins alpha and beta. The nature of the isomerism was determined by chemical interconversion experiments and spectroscope analysis to be a change in configuration at C-21. Evidence is provided for other cases of this type of isomerism in the elfamycin class of antibiotics.