A new approach to the synthesis of oligonucleotides and their phosphorothioate analogues in solution

A new approach to the synthesis of oligonucleotides and oligonucleotide phosphorothioates in solution is described; it is based on H-phosphonate coupling at −40°C, followed by in situ sulfur-transfer with either N-[(4-chlorophenyl)sulfanyl]phthalimide19 or 4-[(2-cyanoethyl)sulfanyl]morpholine-3,5-dione 21.