Oligonucleotide synthesis involving deprotection of amidine-type protecting groups for nucleobases under acidic conditions.

Amidine-type protecting groups, i.e., N,N-dimethylformamidine (dmf) and N,N-dibutylformamidine (dbf) groups, introduced into nucleobases were rapidly removed under mild acidic conditions using imidazolium triflate (IMT) or 1-hydroxybenztriazole (HOBt). This new deprotection strategy allowed a 2'-O-methyl-RNA derivative bearing a base-labile group to be efficiently synthesized using a silyl-type linker. It was also found that our new method could be applied to the synthesis of an unmodified RNA oligomer.