Lack of influence of the carbamoyl group on the stereochemistry of the acid-catalyzed opening of the aziridine ring of the mitomycins and of congeners

The acid-catalyzed opening of the aziridine ring of mitomycins A and C is known to occur predominantly with cis stereochemistry. We have observed that the presence or absence of a carbamoyl group at C-10 of mitomycin C and in certain of its analogues does not have a significant influence on the stereochemistry of the opening of this ring. The trans product obtained from mitomycin C was shown to be stable when treated with acid under the conditions of its formation. Mitomycin B was also shown to yield predominantly the cis product when it was subjected to acid-catalyzed opening of its aziridine ring. The 1H NMR spectra of acetate derivatives prepared from mitomycin B show two sets of signals that are due to two populations of rotamers. The analysis of these spectra has substantiated several previous spectral assignments. This paper also presents some thoughts on acid-catalyzed bifunctional DNA alkylation by mitomycins and 10-decarbamoyloxy-9-dehydromitomycins.