Synthesis of 3′-deoxy-3′-carboxymethylnucleosides, precursors of oligonucleotides with an amide internucleoside bond

An improved method for the synthesis of 3-deoxy-3-carboxymethyl nucleosides was suggested. Oxidation of 5- O -benzoyl-1,2- O -isopropylidene-α- D -xylofuranose resulted in the 3-keto derivative, which was treated with triethylphosphonoacetate in the presence of sodium hydride to obtain the 3-deoxy-3-ethoxycarbonylmethylene derivative. Hydrogenation of the unsaturated compound proceeded strictly stereospecifically and gave the product with the ribo -configuration. Acetolysis of the resulting compound with AcOH-Ac 2 O-CH 3 SO 3 H led to 1,2-di- O -acetyl-5- O -benzoyl-3-deoxy-3-ethoxycarbonylmethyl- D -ribofuranose, whose interaction with persilylated nucleic bases gave 3-deoxy-3-ethoxycarbonylmethylnucleosides in a total yield of 42–49% from the starting compound.