O 4 -Alkylated-2-Deoxyuridine Repair by O 6 -Alkylguanine DNA Alkyltransferase is Augmented by a C5-Fluorine Modification.

Oligonucleotides containing various adducts, including ethyl, benzyl, 4-hydroxybutyl and 7-hydroxyheptyl groups, at the O ⁴ atom of 5-fluoro-O ⁴ -alkyl-2'-deoxyuridine were prepared by solid-phase synthesis. UV thermal denaturation studies demonstrated that these modifications destabilised the duplex by approximately 10 °C, relative to the control containing 5-fluoro-2'-deoxyuridine. Circular dichroism spectroscopy revealed that these modified duplexes all adopted a B-form DNA structure. O ⁶ -Alkylguanine DNA alkyltransferase (AGT) from humans (hAGT) was most efficient at repair of the 5-fluoro-O ⁴ -benzyl-2'-deoxyuridine adduct, whereas the thymidine analogue was refractory to repair. The Escherichia coli AGT variant (OGT) was also efficient at removing O ⁴ -ethyl and benzyl adducts of 5-fluoro-2-deoxyuridine. Computational assessment of N1-methyl analogues of the O ⁴ -alkylated nucleobases revealed that the C5-fluorine modification had an influence on reducing the electron density of the O ⁴ -C _α bond, relative to thymine (C5-methyl) and uracil (C5-hydrogen). These results reveal the positive influence of the C5-fluorine atom on the repair of larger O ⁴ -alkyl adducts to expand knowledge of the range of substrates able to be repaired by AGT.
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