LAUSR

Oligonucleotides containing various adducts, including ethyl, benzyl, 4‐hydroxybutyl and 7‐hydroxyheptyl groups, at the O4 atom of 5‐fluoro‐O4‐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. O6‐Alkylguanine DNA alkyltransferase (AGT) from humans (hAGT) was most efficient at repair of the 5‐fluoro‐O4‐benzyl‐2′‐deoxyuridine adduct, whereas the thymidine analogue was refractory to repair. The Escherichia coli AGT variant (OGT) was also efficient at removing O4‐ethyl and benzyl adducts of 5‐fluoro‐2‐deoxyuridine. Computational assessment of N1‐methyl analogues of the O4‐alkylated nucleobases revealed that the C5‐fluorine modification had an influence on reducing the electron density of the O4−Cα 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 O4‐alkyl adducts to expand knowledge of the range of substrates able to be repaired by AGT.