When a special nucleoside is required, it is necessary for users to prepare a phosphoramidite themselves. A phosphoramidite is prepared by reacting an amidite synthetic reagent such as 2-cyanoethyl N,N,N',N'-tetraisopropyl phosphorodiamidate with nucleosides protected at appropriate positions. Before the reaction, protection of the 5'-hydroxyl group is required. FUJIFILM Wako also introduces tritylation reagents (trityl chloride derivatives) and organic bases used for this protection.