Use of phosphorus oxychloride in synthesizing nucleotides and oligonucleotides

Procedures are described for phosphorylating protected nucleotides, oligonucleotides and phosphoramidate oligonucleotide derivatives at the 3′-hydroxyl group. The conditions (phosphorylation with phosphorus oxychloride and pyridine in dioxane followed by hydrolysis with aqueous pyridine) are sufficiently mild that base labile (trifluoroacetylamino; β-cyanoethyl phosphotriester) and acid labile (O-monomethoxytrityl; phosphoramidate) functions are retained intact. Application of the technique is illustrated by the synthesis of dpT, dTp, d(CF₃CONH)Tp, dTp_NTp, and dTp_NTp_NTp. In addition, the utilization of phosphorus oxychloride in joining thymidine derivatives and dinucleoside phosphotriester blocks via phosphodiester links is described.