The preparation of fully protected labeled diisopropylamino-β-cyanoethyl-[1′-13C] ribonucleoside phosphoramidites with regioisomeric purity is described. We demonstrated in this paper that a regioselective 2′-O-silylation, through a 3′, 5′-O-di-tert- butylsilanediyl protection, has been applied for the synthesis of [1′-13C] ribonucleoside phosphoramidite units. This method allowed us to obtain only the desired 2′-O-silyl-3′- ...