P-32-postlabelling of diastereomeric 7-alkylguanine adducts of butadiene monoepoxide

The reaction of 3,4-epoxy-1-butene (BMO) with deoxyguanosine-3' -monophosphate (3'-dGMP) resulted in the formation of two pairs of diastereomeric 7-alkyl-3'-dGMP derivatives corresponding to two isomers C ''-1 and C ''-2, The T4 polynucleotide kinase-mediated phosphorylation with [gamma-P-32]-ATP showed preferential labelling of diastereomers of the C ''-1 isomer. The diastereomers 1 and 2 of the C ''-1 isomer had labelling efficiencies of 42%. However, the labelling efficiencies of diastereomers 3 and 4 of the C ''-2 isomer were 11 and 10%, respectively. The P-32-postlabelling of BMO-modified DNA yielded four isomers in the ratio of 4:4:1:1 with overall recoveries being 14%. The two isomers had a half-life of 270 min (C ''-1 isomer) and 300 min (C ''-2 isomer) which is in accordance with the stability predicted by other similar adduct experiments. The molecular modelling experiments showed more pronounced restricted rotation of butadiene residue in C ''-2 isomers due to steric interaction between butadiene residue at N-7 and O-6 atom of guanine than in C ''-1 isomer. The butadiene residue also leads to steric overcrowding at 3'-phosphate in C ''-2 isomer which probably restricts the access to the active site of T4 polynucleotide kinase.