Problems of the Synthesis of Oligonucleotide Derivatives in the Realization of the Anchimeric Effect

It has been found that the presence of a free OH group at the 3'-terminal residue of the substituted ethylene glycol fragment in a phosphoryl guanidine oligodeoxyribonucleotide derivative is a factor that determines the instability of the structure of the target oligonucleotide product under the conditions of a standard deblocking protocol. It has been shown that the main by-products of the realization of the anchimeric effect of the OH group are the products of the transesterification of the phosphoryl guanidine (PG) unit carrying the O-substituted ethylene glycol residue. The data of the mass spectrometry analysis indicate that, under alkaline conditions, the accumulation of derivatives devoid of the N,N,N',N'-substituted guanidine residue (1,3-dimethylimidazolidin-2-imine, DMI) or the entire 3'-terminal PG-containing nonnucleotide unit occurs.