Patent ID: 8569476

Claim:
A method for preparing an oligonucleotide, comprising reacting the compound represented by Formula (1) with the compound represented by Formula (2) in a liquid reaction medium under the condition of condensation reaction to obtain the compound represented by Formula (3), wherein 1-(2-mesitylenesulfonyl)-3-nitro-1H-1,2,4-triazole (MSNT) is applied as condensing agent, and wherein: R 1 represents 4,4′-dimethoxytriphenylmethyl, or a covalently attached 5′-substituent derived from RNA or from DNA; R 2 and R 3 independently represent a sterically hindered trisubstituted silyl protective group; R 4 represents a halogen atom; A + represents a tri-alkyl ammonium ion; B 1 and B 2 independently represent 9-guaninyl substituted with N-acyl, 9-adeninyl substituted with N-acyl, 1 cytosinyl substituted with N-acyl, 1-thyminyl or 1-uracilyl; and with the proviso that in Formula (1) or (3), —CH 2 —N 3 is at an ortho-position.