Conjugation of a hairpin pyrrole-imidazole polyamide to a quinone methide for control of DNA cross-linking.

A series of quinone methide precursors designed for DNA cross-linking were prepared and conjugated to a pyrrole-imidazole polyamide for selective association to the minor groove. Although reaction was only observed for DNA containing the predicted recognition sequence, yields of strand alkylation were low. Interstrand cross-linking was more efficient than alkylation but still quite modest and equivalent to that generated by a comparable conjugate containing the N-mustard chlorambucil. Varying the length of the linker connecting the polyamide and quinone methide derivative did not greatly affect the yield of DNA cross-linking. Instead, intramolecular trapping of the quinone methide intermediate by nucleophiles of the attached polyamide appears to be the major determinant that limits its reaction with DNA. Self-adducts of the quinone methide conjugate form readily and irreversibly as detected by a combination of chromatography and mass spectroscopy. This result is unlike comparable self-adducts observed for oligonucleotide conjugates that form more slowly and remain reversible. Equivalent intramolecular alkylation of a polyamide by its attached chlorambucil mustard was not observed under similar condition. The presence of DNA, however, did facilitate hydrolysis of this mustard conjugate.