Studies on N4-(2-deoxy-D-pentofuranosyl)-4,6-diamino-5-formamidopyrimidine (Fapy•dA) and N6-(2-deoxy-D-pentofuranosyl)-6-diamino-5-formamido-4-hydroxypyrimidine (Fapy•dG)

Exposure of DNA to oxidative stress produces a variety of DNA lesions including the formamidopyrimidines, which are derived from the purines. These lesions may play important roles in carcinogenesis. We achieved the first chemical syntheses of a monomeric form of Fapy.dA (1) and oligonucleotides containing this lesion or Fapy.dG at a defined site. Monomeric Fapy.dA readily epimerized at 25degreesC in phosphate buffer (pH 7.5). The beta-anomer was favored by a ratio of 1.33:1.0, and equilibration was achieved in less than 7 h. Deglycosylation of Fapy.dA in the monomer follows first-order kinetics from 37 to 90.C. The rate constants for deglycosylation of Fapy.dA in the monomeric and oligonucleotide substrates were measured at a common temperature (55degreesC) and found to be the same within experimental error (t(1/2) = 20.5 h). Implementation of the activation parameters measured for the deglycosylation of I indicates that the half-life for deglycosylation of Fapy.dA at 37degreesC is approximately 103 h. Analysis of the rate constant for deglycosylation of Fapy.dG in an oligonucleotide, revealed that this lesion is similar to25 times more resistant to hydrolysis than Fapy.dA at 55degreesC. These results indicate that Fapy.dA and Fapy.dG will be sufficiently long-lived in DNA so as to warrant investigation of their genotoxicity, and both anomers will be present during this time.