method
The phosphoramidite method of DNA synthesis is currently considered as the standard synthesis method used in most automated synthesizers today. This method allows achieving the high coupling efficiencies needed to synthesize longer and longer oligonucleotides with low amounts of failure sequences. The oligonucleotide phosphoramidite synthesis chemistry was introduced nearly 20 years ago (McBride and Caruthers, 1983). Building blocks used for synthesis are commonly referred to as “monomers”, which are activated DNA nucleosides (phosphoramidites). The dimethoxytrityl (DMT) group is used to protect the 5’-end of the nucleoside, a β-cyanoethyl group protects the 3’-phosphite moiety, and may also include additional groups that serve to protect reactive primary amines in the heterocyclic nucleo bases. The protecting groups are selected to prevent branching or other undesirable side reactions from occurring during synthesis. Oligonucleotides are synthesized on solid supports. Typically, the support is a small column filled with control pore glass (CPG), polystyrene or a membrane. The oligonucleotide is usually synthesized from the 3’ to the 5’. The synthesis begins with the addition of a reaction column loaded with the initial support-bound protected nucleotide into the column holder of the synthesizer. The first nucleotide building block or monomer is usually anchored to a long chain alkylamine-controlled pore glass (LCAA-CPG).
A schematic diagram general outline the solid phase oligonucleotide synthesis of a dinucleotide is illustrated below.