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Development of new N-unprotected phosphoramidite building blocks having a silyl-type linker.

New silyl-type linkers 2 and 3 were developed for the synthesis of oligonucleotides having base-labile functional groups in the phosphoramidite method without base protection. These linkers could be introduced into polymer supports in high yields and easily cleaved under neutral conditions. Particularly, the use of the N-unprotected phosphoramidite building block 3 having a silyl-type linker enabled us to synthesize oligodeoxynucleotides without protecting groups for the amino groups of 3'-terminal deoxyribonucleosides.