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Utility of 5'-O-2,7-dimethylpixyl for solid-phase synthesis of oligonucleotides containing acid-sensitive 8-aryl-guanine adducts.

To study the structural and biological impact of 8-aryl-2'-deoxyguanosine adducts, an efficient protocol is required to incorporate them site-specifically into oligonucleotide substrates. Traditional phosphoramidite chemistry using 5'-O-DMT protection can be limiting because 8-aryl-dG adducts suffer from greater rates of acid-catalyzed depurination than dG and are sensitive to the acidic deblock conditions required to remove the DMT group. Herein we show that the 5'-O-2,7-dimethylpixyl (DMPx) protecting group can be used to limit acid exposure and improve DNA synthesis efficiency for DNA substrates containing 8-aryl-dG adducts. Our studies focus on 8-aryl-dG adducts with 8-substituents consisting of furyl ((Fur)dG), phenyl ((Ph)dG), 4-cyanophenyl ((CNPh)dG), and quinolyl ((Q)dG). These adducts differ in ring size and sensitivity to acid-promoted deglycosylation. A kinetic study for adduct hydrolysis in 0.1 M aqueous HCl determined that (Fur)dG was the most acid-sensitive (55.2-fold > dG), while (Q)dG was the most resistant (5.6-fold > dG). The most acid-sensitive (Fur)dG was chosen for optimization of solid-phase DNA synthesis. Our studies show that the 5'-O-DMPx group can provide a 4-fold increase in yield compared to 5'-O-DMT for incorporation of (Fur)dG into DNA substrates critical for determining adduct impact on DNA synthesis and repair.