Development of an N-unprotected phosphoramidite method for the chemical synthesis of aminoacylated RNAs

Abstract

In the previous study, we developed a method for O-selective phosphorylation, i.e., "the activated phosphite method" for DNA synthesis without base protection. However, the O-selectivity was low in RNA synthesis when the activated phosphite method was used. In this paper, we developed a new method for the O-selective phosphorylation available for the chemical synthesis of aminoacylated RNAs on polymer supports. As the result, it was found that the selectivity of the phosphorylation in RNA synthesis without base protection increased to more than 99% by treatment of the undesired N-P(III) bonds with 1-hydroxyl-6-nitorobenzotriazole, independent of the kind of protecting groups at the 2' position. Moreover, we succeeded in synthesizing a 21 mer oligoRNA without base protection.

Solid-phase synthesis of base-sensitive oligonucleotides

“…re In order to combine a good O-selectivity with a high yield, several HOBt derivatives have been screened for the phosphite triester coupling. 87 89 However, the required longer coupling time lowers the O-selectivity. The shortcoming may be resolved by a NBT (107) promoted post-condensation treatment, which increased the selectivity to more than 99% independently on the kind of protecting groups (TDMS, TOM) at the 2'-position.…”