[Synthesis of 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides, the precursors of oligonucleotides with the amide internucleoside bond C3'-NH-C(O)-CH2-C5'].

A method for the synthesis of 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides has been developed. 3-O-Benzyloxymethyl-1,2-O-isopropylidene-alpha-D-allofuranose was oxidized by sodium periodate to form a 5-aldo derivative, which was converted by the reaction with triethylphosphonoacetate in the presence of sodium hydride into a 5-deoxy-5-ethoxycarbonylmethylene derivative. The hydration of the unsaturated compound gave 5-deoxy-5-ethoxycarbonylmethyl-l,2-O-isopropylidene-alpha-D-ribofuranose. After the benzylation of 3-hydroxyl, the removal of the isopropylidene group by heating with acetic acid, and the subsequent acetylation, l,2-di-O-acetyl-3-O-benzyl-5-deoxy-5-ethoxycarbonylmethyl-D-ribofuranose was obtained, which reacted with persilylated nucleic acid bases to form 5'-deoxy-5'-ethoxycarbonylmethyl nucleosides.