For large scale oligonucleotide synthesis, the Phosphoramidite method is the most widely used method, which is a kind of solid phase synthesis.
The synthesis cycle mainly include four steps.
Detritylation: Generation of a free 50 -OH group (free_OH) by removal of the 50 -OH protection group (DMT) using an organic acid (e.g., dichloroacetic acid).
Coupling: Prolongation of the oligonucleotide chain by reaction of the free 5’-OH group with a phosphoramidite (amidite), which is activated by a so called activator (for example 1H-tetrazole21).
Oxidation: Oxidation of the 1III phosphor of the newly attached nucleoside to 1V with an oxidation reagent (e.g., aqueous iodine solution).
Capping: Blocking of nonreacted 50 -OH groups by acetylation.