Base sequence selectivity in the alkylation of DNA by 1,3-dialkyl-3-acyltriazenes

The base sequence selectivity of DNA alkylation for a series of structurally related 1,3-dialkyl-3-acyltriazenes was examined with calf thymus DNA or polymers containing the sequences GGG, CGC, TGT, and AGA. The reaction products at the N7 and the O6 positions of guanine were identified, quantitated, and then correlated with the decomposition rates of the triazenes, 1-(2-chloroethyl)-3-methyl-3-carbethoxy- (CMC), 1-(2-chloroethyl)-3-methyl-3-acetyl- (CMA), 1-(2-hydroxyethyl)-3-methyl-3-carbethoxy- (HMC), 1-(2-hydroxyethyl)-3-methyl-3-acetyl- (HMA), and 1,3-dimethyl-3-acetyl- (DMA). The results of these studies revealed that DNA sequences with runs of purines were more reactive toward alkylation by all of the triazenes tested, irrespective of whether the alkylation was measured by N7, O6, or total guanine adducts. Within this generalization, the (hydroxyethyl)triazenes showed a preference for the AGA sequence, while the (chloroethyl)triazenes favored the GGG sequence. The structure of the 3-acyl group of the triazene also played a role in the extent of alkylation of a particular sequence of DNA. Both the (chloroethyl)- and the (hydroxyethyl)triazenes produced higher alkylation product yields for the 3-carbethoxytriazenes as compared with the 3-acetyl derivatives for most of the sequences examined. These overall patterns correlated well with the order of decomposition of the triazenes at 37 degrees C: HMC > DMA > HMA > CMC > CMA. This study has demonstrated how varying the structure of 1,3-dialkyl-3-acyltriazenes can modulate DNA alkylation, a finding which may be important in the design of new triazene antitumor agents.