[Oligonucleotide analogues containing a C3'-NH-C(O)-CH(2)-C5' amide internucleotide bond]

A dinucleoside containing a C3'-NH-C(O)-CH(2)-C5' amide internucleoside bond was synthesized by the interaction of 3'-deoxy-3'-amino-5'-O-(tert-butyldimethylsilyl)thymidine with 3'-O-benzoyl-2'-O-tert-butyldimethylsilyl-5'-deoxy-5'-carboxymethylribosylthymine, which was obtained from 2'-O-acetyl-3'-O-benzyl-5'-deoxy-5'-ethoxycarbonylmethylribosylthymine through the methanolysis of the acetyl group followed by silylation and ester saponification. After standard manipulation with protecting groups, the dinucleoside was converted into 3'-O-(2-cyanoethyl-N,N-diisopropylphosphoramidite), which was used for the synthesis of modified oligonucleotides on an automated synthesizer. The melting curves of the duplexes formed by modified and complementary natural oligonucleotides were registered, and the melting temperatures and thermodynamic parameters of the duplex formation were calculated. The introduction of a single modified bond into the oligonucleotide led to an insignificant decrease in the melting temperature of these duplexes as compared to unmodified ones.