A Novel Method for Oligonucleotide Synthesis on the Basis of Chemoselective Phosphonylation

Abstract

A novel method for oligonucleotide synthesis on the basis of chemoselective phosphonylation is described. Nucleoside 3́-H-phosphonate monomers without amino protection were synthesized by the O-selective phosphonylation of nucleosides bearing the free amino and 3́-hydroxy groups. It was found that the amino groups of nucleosides were not modified during internucleotidic bond formation when carbenium and phosphonium compounds were employed as condensing reagents in the present H-phosphonate method. A mechanism for the O-selective condensation was investigated in detail by means of 31P NMR spectroscopy as well as ab initio molecular orbital calculations. The internucleotidic H-phosphonate linkages were oxidized with N-sulfonyloxazilidine derivatives in the presence of silyating reagents under unhydrous conditions without degradation of the oligonucleotide chain. The present method was found to be effective for the synthesis of base-sensitive DNA derivatives bearing various functional groups.