The chemical synthesis of oligoribonucleotides. IX. A comparison of protecting groups in the dichloridite procedure

A series of phosphorodichloridites bas been prepared incorporating the most commonly used phosphate protecting groups in oligonucleotide synthesis. The groups include trichloroethyl, tribromoethyl, cyanoethyl, benzyl, methyl, p-chlorophenyl, and nitrophenethyl. The trichloroethyl and the nitrophenethyl appear to be the most stable groups while the cyanoethyl and methyl offer specific advantages. The benzyl and p-chlorophenyl groups are subject to limitations on their utility. Condensations can be carried out in a range of solvents including THF, pyridine, and DMF and at temperatures from −78 °C to 20 °C with a slight drop in yield with increasing temperature, at least for dinucleotide condensations.