The synthesis of the internucleotide (phosphodiester) bond by a base-catalysed reaction.

Potassium tert-butoxide in hexamethyl phosphoramide and dimethyl formamide provides an excellent catalyst for the reaction of a 3'-hydroxyl or a 5'-hydroxyl group of a nucleoside with an appropriate nucleoside phosphorofluoridate to yield the dinucleoside phosphate. This paper describes the experiments leading to the development of this reaction together with the synthesis of thymidylyl-(5' leads to 3')-thymidine (dT-dT).