31P NMR Study of the Mechanism of Activation and Coupling Reactions in the Synthesis of Oligodeoxyribonucleotides by the Phosphotriester Method

Article abstract of DOI:10.1021/jo00199a039

The phosphotriester method provides a rapid and convenient procedure for synthesizing oligonucleotides.The mechanism has been revealed and intermediates have been identified by ³¹P NMR methodology.It was found that reaction of a 5'-protected nucleoside 3'-(p-chlorophenyl phosphate) with mesitylenesulfonyl chloride (MSCl) or 1-(mesitylyl-2-sulfonyl)-3-nitro-1,2,4-triazole (MSNT) in anhydrous pyridine yields only two products within 5 min, the sulfonic acid-phosphate mixed anhydride 2 and the (3'-3') symmetrical pyrophosphate tetraester 3 which can be isolated as a mixture.Reaction of 2 and 3 with 3'-O-acetylthymidine yields the phosphotriester dimer <(MeO)2Tr>NpTOAc.The reaction rate and yield of dimers are closely dependent on the presence of catalysts.The reaction finished within minutes when tetrazole or 3-nitro-1,2,4-triazole was used.On the contrary, the reaction completed in hours when imidazole or 1,2,4-triazole was used as catalysts.The possible mechanisms are explored and discussed in detail.