Stereochemistry of internucleotide bond formation by the H-phosphonate method. 1. Synthesis and 31P NMR analysis of 16 diribonulceoside (3'-5')-H-phosphonates and the corresponding phosphorothioates.

Sixteen diribonucleoside (3'-5')-H-phosphonates were synthesized via condensation of the protected ribonucleoside 3'-H-phosphonates with nucleosides, and the influence of a nucleoside sequence on the observed stereoselectivity was analyzed. 31P NMR spectroscopy was used to evaluate a relationship between chemical shift and absolute configuration at the phosphorous center of the H-phosphonate diesters as well as of the corresponding phosphorothioate diesters. Although for the most cases such correlation was found, there was however several exceptions to the rule where the relative positions of resonances arisingfrom Rp and Sp diastereomers were reversed.