Development of a new synthetic method for oligodeoxynucleotides using 3′-H-phosphonamidate derivatives

In this study, we developed a new approach for the solution-phase synthesis of oligodeoxynucleotides (ODNs) using nucleoside 3′-H-phosphonamidate derivatives as monomers. The H-phosphonamidate monomers having a heterocyclic amino group as the leaving group reacted with an alcohol to form an internucleotidic H-phosphonate diester under mild basic conditions without using additives. The resultant internucleotidic linkage was converted into a more stable linkage, such as an S-cyanoethyl phosphorothioate diester. Moreover, under the conditions for detritylation, the unreacted H-phosphonamidate monomer was converted into a water-soluble compound, which was easily removed by extraction. Thus, only simple extractions were required to purify intermediates, and the solution-phase synthesis of trithymidine diphosphorothioate from the monomer was achieved with only one silica gel column chromatography purification. This method was applied to deoxyadenosine, deoxycytidine, and deoxyguanosine derivatives. This strategy enables us to reduce the number of reagents and simplify the purification process.