The merits of N-unsubstituted indoles and cyclopent [b] indoles as DNA-directed reductive alkylating agents are described. These systems represent a departure from N-substituted and pyrrolo [1, 2-a]-fused systems such as the mitomycins and mitosenes. The cyclopent [b] indole-based aziridinylquinone system, when bearing an acetate leaving group with or without an N-acetyl group, was cytotoxic and displayed significant in vivo activity against ...