Patent ID: 7635772

Claim:
A process for the synthesis of an oligonucleotide in which an oligonucleotide is assembled on a swellable solid support using the phosphoramidite approach in the presence of a solvent and an activator, wherein, the solvent and swellable support are selected such that a swell ratio of from 5 to 20 is achieved, swell ratio being calculated according to the formula: Swell ⁢ ⁢ Ratio = Vol final - Vol initial Vol initial wherein Vol final is the final volume occupied by the swellable support after full swelling; and Vol initial is the initial dry bed volume of the swellable support, the activator being selected from the group consisting of i) compounds having the chemical formula (1): wherein p is 0 or an integer from 1 to 4; X is O or S; and R for each occurrence is a substituent selected from the group consisting of halo groups, aliphatic groups, —NR 1 R 2 , —OR 3 , —OC(O)R 3 , —C(O)OR 3 , cyano, aryl groups, heterocyclyl groups, —CHO, —COR 3 , —NHCOR 3 , aralkyl groups, and —SR 13 , wherein R 11 and R 12 are each, independently, —H, an aliphatic group, an aryl group, an aralkyl group; or together with the nitrogen to which they are attached form a 5 or 6-membered heterocyclic ring; and R 13 is an aliphatic group, an aryl group, or an aralkyl group; or two adjacent R groups taken together with the carbon atoms to which the are attached form a six membered saturated or unsaturated ring; and ii) salts formed between a compound of chemical formula (1) and an organic base.