Abstract
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; beta-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(CF(3)CONH)Tp, dTp(N)Tp, and dTp(N)Tp(N)Tp. In addition, the utilization of phosphorus oxychloride in joining thymidine derivatives and dinucleoside phosphotriester blocks via phosphodiester links is described.