DNA ALKYLATION PROPERTIES OF CC-1065 AND DUOCARMYCIN ANALOGS INCORPORATING THE 2,3,10,10A-TETRAHYDROCYCLOPROPA[D]BENZO[F]QUINOL-5-ONE ALKYLATION SUBUNIT - IDENTIFICATION OF SUBTLE STRUCTURAL FEATURES THAT CONTRIBUTE TO THE REGIOSELECTIVITY OF THE ADENINE N3 ALKYLATION REACTION

The DNA alkylation properties of (-)- and ent-(+)-CBQ-TMI and (-)- and ent-(+)N-BOC-CBQ, analogs of the duocarmycins incorporating the reactive 2,3,10,10a-tetrahydrocyclopropa[d]benzo[f]quinol-5-one (CBQ) alkylation subunit, are detailed. The agents were found to alkylate the same sites as the corresponding enantiomers incorporating the DSA, DA, CPI, CBI, or CI alkylation subunit. Consistent with their reactivity, they exhibited less selectivity among the available alkylation sites and alkylated DNA with a lower efficiency. Importantly, only adducts derived from adenine N3 addition to the least substituted cyclopropane carbon were detected under the relevant conditions of limiting agent. The adenine N3 adduct obtained by thermal depurination was isolated, quantitated, characterized, and shown to be derived from addition to the least substituted cyclopropane carbon of CBQ-TMI. Since the CBQ-based agents exhibit nonselective solvolysis regioselectivity with cleavage of both the normal external C9b-C10 and the abnormal internal C9b-C10a cyclopropane bonds, the observations suggest that the clean regiochemical course of the characteristic adenine N3 DNA alkylation reaction may benefit from not only the stereoelectronic control but additional features that complement the normally observed regioselectivity as well. These potentially include preferential adoption of binding orientations that favor the normal adenine N3 addition (proximity effects), and destabilizing torsional strain and steric interactions that accompany the abnormal adenine N3 nucleophilic addition, as well as a potential binding induced conformational change in CBQ which imposes a stereoelectronic preference for adenine N3 addition to the least substituted cyclopropane carbon.