The key step in the use of any universal support in oligonucleotide synthesis is the dephosphorylation of the 3'-phosphate group to form the desired 3'-hydroxyl group. Azhayev1,2 has excelled in the investigation of neighboring group assistance in the dephosphorylation reaction. Amide groups may be considered to be weak N‑H acids and can display basic properties in ammonium hydroxide or aqueous methylamine. In the original work1,2 (±)-3-Amino-1,2-propanediol was used to form a novel universal support(1). A succinate linker attaches the 3-amino group to the support and the 2-OH is protected with a base-labile group to set up an amide assisted elimination in mildly basic conditions. In this way, the dephosphorylation reaction would eliminate the desired 3'-OH oligonucleotide into solution and the product of any β-elimination competing side reaction would remain bound to the support. A further improvement has been achieved by using a carbamate group to connect the universal linker to the support, now called Universal Support III. The structures of the two supports are shown below right. Because the universal linker is unchanged and the succinate or carbamate groups remain attached to the support, as in product Universal Support III (2). Using Universal Support III, an oligo yield of > 80% can be achieved on polymeric supports, with purity equivalent to the same oligo prepared normally.
Conditions for Cleavage and Deprotection are outlined in the table opposite. Universal Support III has been shown to generate oligonucleotides with the same efficacy in polymerase extension reactions as regular oligos. Despite the mild elimination reaction, oligonucleotides up to 75mer in length can be prepared routinely without loss of oligo during the synthesis cycles. This support is also used for the production of siRNA oligos.