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 [w/-15N]-2'-deoxyadenosine and [3-15N]-2'deoxyuridine derivatives. The substitution effects on the NMR parameters were linearly correlated with the pKa values of the 2'deoxyuridine derivatives.