OLIGONUCLEOTIDE MANUFACTURING METHOD

The present invention aims to provide a more stable and efficient method for producing oligonucleotide, particularly, oligonucleotide having various functional groups linked to the 3′-terminal and the like. Efficient production of oligonucleotide becomes possible by a production method of an oligonucleotide represented by the formula (Ia-2) (each symbol is as defined in the DESCRIPTION) and having a functional group at the 3′-terminal, the method including a step of subjecting an oligonucleic acid with 3′-terminal protected by a silyl-protecting group to 3′-terminal-selective deprotection under desilylation conditions that do not affect protecting groups other than the silyl group, subjecting same to phosphitylation conditions with a phosphoramidite reagent that do not affect protecting groups on the oligonucleic acid to give a 3′-terminal-phosphoramidited oligonucleotide represented by the formula (Ia-1) (each symbol is as defined in the DESCRIPTION), and linking a functional group to the 3′-terminal of the 3′-terminal phosphoramidited oligonucleotide directly or via a linker, and the like.