The H-phosphonate approach to the synthesis of oligonucleotides and their phosphorothioate analogues in solution

Abstract

A new approach to the synthesis of oligonucleotides and oligonucleotide phosphorothioates in solution is described; it is based on H-phosphonate coupling [with bis(2-chlorophenyl) phosphorochloridate 22 as the coupling agent] at –40 °C, followed by in situ sulfur transfer involving either 2-(4-chlorophenylsulfanyl)isoindole-1,3(2H)-dione 23a or 4-[(2-cyanoethyl)sulfanyl]morpholine-3,5-dione 26. The yields of the coupling and sulfur transfer reactions are virtually quantitative and, following unblocking by previously reported procedures, very pure products (d[ApC], d[TpGpApC], d[TpGp(s)ApC], d[Gp(s)A] and d[Cp(s)Tp(s)Gp(s)A]) are obtained.