Mitomycin Imp. B (EP): (1aS,8S,8aR,8bS)-8-[[(Aminocarbonyl)oxy]methyl]-1,1a,2,8,8a,8b-hexahydro-6,8a-dimethoxy-5-methylazirino [2’,3’:3,4]pyrrolo[1,2-a]indole-4,7-dione (Mitomycin A).