A unique class of N-acyl O-amino phenol prodrugs of CBI-TMI and CBI-indole2 were synthesized and shown to be prodrugs, subject to reductive activation by nucleophilic cleavage of a weak N—O bond, effectively releasing the free drug in functional cellular assays for cytotoxic activity approaching or matching the activity of the free drug, yet remain essentially stable to ex vivo DNA alkylation conditions. Most impressively, assessment of the in vivo antitumor activity of a representative O-(acylamino) prodrug, 8, indicate that they approach the potency and exceed the efficacy of the free drug itself (CBI-indole2), indicating that the inactive prodrugs not only effectively release the free drug in vivo, but that they offer additional advantages related to a controlled or targeted release in vivo.