Synthesis of 5-substituted [N3-15N]-pyrimidine nucleosides: Developing model systems for NMR studies of substituent effects on the N-H...N hydrogen bond in duplex DNA.

The effects on various NMR parameters of substitutions, which may influence the hydrogen bond strengths of Watson-Crick-type base pairs, were investigated for DNA dodecamers containing 5-substituted-2'-deoxyuridine derivatives in oligomers, 5'-d(CGCGAATXCGCG)-3', where A and X were [ul-15N]-2'-deoxyadenosine and [3(-15)N]-2'-deoxyuridine derivatives. The substitution effects on the NMR parameters were linearly correlated with the pKa values of the 2'-deoxyuridine derivatives.