MONOFUNCTIONAL AND DIFUNCTIONAL NITROGEN-MUSTARD ANALOGS OF THE DNA MINOR-GROOVE BINDER PIBENZIMOL - SYNTHESIS, CYTOTOXICITY AND INTERACTION WITH DNA

Two series of mono-and difunctional aniline mustards linked to a bisbe nzimidazole minor groove binder have been prepared using a new method (polyphosphate ester-mediated direct coupling of appropriate mustard a cids with a preformed advanced phenylenediamine intermediate). As the linker chain attaching the mustard was lengthened the binding site siz e of the compounds to calf thymus DNA remained essentially constant at 2.6 nucleotides, but reversible binding strength declined by a factor of 2. Analogues with longer linker chains alkylated DNA much more rap idly than those with shorter chains, consistent with the electronic fa ctors. The short chain analogues also failed to alkylate a 120 bp Hind III to Bg/II fragment of the gpt gene, as measured by gel electrophore sis cleavage assays. The longer chain analogues (both mono- and difunc tional mustards) showed patterns of DNA alkylation that varied with ch ain length. In particular, while most compounds showed substantial N7 alkylation at many guanine residues, the analogue with a (CH2)(3) link er chain showed strong alkylation at adenine sites in poly-AT regions. For the longer chain analogues, the bifunctional mustards were substa ntially (10- to 20-fold) more cytotoxic than the corresponding monofun ctional analogues.