Figure 41.1 The synthesis of a DNA strand by the phosphite triester method. The activated monomer added to the growing strand is a deoxyribonucleoside 3′-phosphoramidite containing a dimethoxytrityl (DMT) protecting group on its 5′-oxygen atom, a β-cyanoethyl (βCE) protecting group on its 3′-phosphoryl oxygen atom, and a protecting group on the base.