THE ROLE OF A QUINONE METHIDE IN THE SEQUENCE-SPECIFIC ALKYLATION OF DNA

Oligonucleotide-naphthoquinone conjugates were prepared and examined f or use as inducible, site-directed alkylating agents of DNA. Reaction was found to be sequence specific and under control of either biomimet ic reduction or near-UV irradiation. Both conditions induced the forma tion of a transient and highly electrophilic intermediate consistent w ith a quinone methide. Enzymatic reduction of 5-((mesyloxy) methyl)- a nd 5-(bromomethyl) naphthoquinone derivatives produced cross-linking b etween a target and probe sequence, but the equivalent 5-(acetoxymethy l), 5-(hydroxymethyl) and 5-methyl analogues were predictably inactive . Conversely, irradiation of the 5-methylnaphthoquinone derivative pro duced cross-linking through a mechanism of photochemical enolization t hat was not available to the 6-methyl, 3-methyl, or unsubstituted anal ogues. Hydroxyl radical footprinting of the modified DNA demonstrated that guanine and cytosine were targets of alkylation.