Effect of sugar modifications on the solution stability of nucleoside phosphoramidites

Oligonucleotide therapeutics represent a rapidly advancing class of medicines that has attracted substantial attention in recent years. Phosphoramidites with chemical modifications are essential building blocks for their chemical synthesis. Therefore, a deep understanding about the stability of phosphoramidites is crucial for the manufacturing of oligonucleotide therapeutics. Especially, it is known that the DNA phosphoramidite with isobutyryl protected-guanine nucleobase (dG[iBu]) is unstable in anhydrous solution. In this study, the solution stabilities of dG[iBu] phosphoramidites with sugar modification were evaluated. The sugar-modified phosphoramidites in acetonitrile were found to be more stable than DNA phosphoramidites, probably due to steric hindrance of the modifications at their 2′-position. Moreover, N,N-dimethylformamide and dichloromethane were identified as alternative solvents that could improve stability without affecting the reactivity of phosphoramidites in oligonucleotide synthesis.