P-32 POSTLABELING OF DIASTEREOMERIC 7-ALKYLGUANINE ADDUCTS OF BUTADIENE MONOEPOXIDE

The reaction of 3,4-epoxy-1-butene (BMO) with deoxyguanosine-3' -monop hosphate (3'-dGMP) resulted in the formation of two pairs of diastereo meric 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 th e C ''-1 isomer. The diastereomers 1 and 2 of the C ''-1 isomer had la belling efficiencies of 42%. However, the labelling efficiencies of di astereomers 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 t he 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 p ronounced restricted rotation of butadiene residue in C ''-2 isomers d ue 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 r estricts the access to the active site of T4 polynucleotide kinase.