Improved Synthesis of Phosphoramidite-Protected N6-Methyladenosine via BOP-Mediated SNAr Reaction.

N6-methyladenosine(m6A) is the most abundant modification in mRNA. Studies on proteins that introduce and bind m6A require the efficient synthesis of oligonucleotides containing m6A. We report an improved five-step synthesis of the m6A phosphoramidite starting from inosine, utilising a 1-H-benzotriazol-1-yloxytris(dimethylamino)phosphoniumhexafluorophosphate (BOP)-mediated SNAr reaction in the key step. The route manifests a substantial increase in overall yield compared to reported routes, and is useful for the synthesis of phosphoramidites of other adenosine derivatives, such as ethanoadenosine, an RNA analogue of the DNA adduct formed by the important anticancer drug Carmustine.