7-N,7′-N′-(1″,2″-Dithianyl-3″,6″-dimethylenyl)bismitomycin C: synthesis and nucleophilic activation of a dimeric mitomycin

Abstract

Dimeric alkylating agents that modify complementary DNA strands have engendered significant interest. We have prepared the novel dimeric mitomycin, 7-N,7′-N′-(1″,2″-dithianyl-3″,6″-dimethylenyl)bismitomycin C (9), in which the mitomycins are bridged by a dithiane unit. Dimer 9, like the clinically tested acyclic disulfides KW-2149 (3) and BMS-181174 (4), was designed to activate under nucleophilic and reductive conditions. Successive nucleophile-mediated disulfide cleavage transformations of 9 are expected to generate thiol species ideally positioned to render the two mitomycin systems vulnerable to nucleophilic attack and permit DNA interstrand cross-link formation. The dithiane linker, strategically positioned between the two mitomycins, distinguished 9 from 3 and 4. Nucleophilic activation of this cyclic disulfide permitted both activated mitomycins to remain tethered to one another. We report the synthesis of 9, and show that the nucleophile Et₃P markedly enhances the activation and consumption of 9, compared with the reference compound 7-N, 7′-N′-(cyclohexanyl-trans-1″,4″-dimethylenyl)bismitomycin C (27). We further demonstrated that 9 provides higher levels of DNA interstrand cross-links than either the dimeric reference compounds, 27 and 7-N,7-N′-(2″,5″-dihydroxy-1″,6″-hexanediyl)bismitomycin C (28), or the monomeric mitomycins, 1 and 3, when Et₃P is added to solutions containing EcoRI-linearized pBR322 DNA.