A new method for introducing amidate linkages in oligonucleotides using phosphoramidite chemistry.

Cyanoethyl-protected phosphotriester links in oligonucleotides made with standard pophosporamidite chemistry were converted to pbosphoramidate linkages during oligonucleotide synthesis on solid support. The cyanoethyl group was removed with piperidine, and the resulting phosphodiester was activated with p-tosyl chloride. An amine nucleophile displaced the tosyl to yield a phosphoramidate linkage.