Chemical Synthesis of Capped Oligoribonucleotides, m7G5′ pppAUG and m7G5′ pppAUGACC

Abstract

The fully-protected pAUG (15) and pAUGACC (21) were synthesized by the phosphotriester approach where the phenylthio group was employed as the internal and 5′-terminal phosphate-protecting groups. The partially unblocked oligomers (32) and (33), obtained by alkaline treatment of (15) and (21), were condensed with a capping reagent (1a) in the presence of imidazole by activation with silver nitrate to afford the capped trimer and hexamer protected with the acid-labile protecting groups, i.e., 4,4,′4″-trimethoxytrityl (TMTr), 4-monomethoxytrityl (MMTr), tetrahydropyran-2-yl (THP), and methoxymethylene (mM) groups. The protected capped oligomers were unblocked by a dilute HCl solution to afford m7G5′ pppAUG and m7G5′ pppAUGACC, which were purified by HPLC and characterized by enzyme assays.