The aminoglycoside antibiotic neomycin B has been converted into several novel building blocks that can be used for the specific modification of three of the four ring systems. Under carefully controlled conditions, the Mitsunobu reaction can be used to selectively dehydrate the ido ring to give the talo epoxide. Subsequently however, under more forcing conditions, the 2-deoxy streptamine ring undergoes Mitsunobu dehydration to give an aziridine. An ...