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)

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Abstract
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 25 °C in phosphate buffer (pH 7.5). The β-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 (55 °C) and found to be the same within experimental error (t1/2 = 20.5 h). Implementation of the activation parameters measured for the deglycosylation of 1 indicates that the half-life for deglycosylation of Fapy•dA at 37 °C is approximately 103 h. Analysis of the rate constant for deglycosylation of Fapy•dG in an oligonucleotide, revealed that this lesion is ∼25 times more resistant to hydrolysis than Fapy•dA at 55 °C. 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.