Base-catalyzed Isomerism in Elfamycin Antibiotics Structures of Ganefromycins ε and ε_1

The structures of ganefromycins e (2a) and e 1 (2b) have been determined by spectroscopic techniques. The compounds are isomeric deoxygenated precursors of the parent antibiotics ganefromycins α and β. The nature of the isomerism was determined by chemical interconversion experiments and spectroscopic 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.