N3'-->P5' Oligodeoxyribonucleotide Phosphoramidates: A New Method of Synthesis Based on a Phosphoramidite Amine-Exchange Reaction.

A new method for the synthesis of N3'-->P5' phosphoramidate oligodeoxynucleotides is demonstrated. Described herein is the synthesis of the monomers utilized in the phosphoramidite amine-exchange process and the experimental details pertaining to this new mode of chain assembly. The phosphoramidite amine-exchange method generates coupling yields in the 92-95% range per cycle and further enables the synthesis of chimeric phosphoramidate/phosphodiester or phosphoramidate/phosphorothioate oligonucleotides with no instrument modifications.