Synthesis of N2-[3-[(trifluoroacetyl)amino]propyl]-5′-O-DMT-O6-(trimethylsilylethyl)-3′-O-[(2-cyanoethyl-N,N′-diisopropyl)phosphoramidite]-2′-deoxyguanosine. a) Ethyl trifluoroacetate and methanol, room temperature, 4 hours; b) 4,4′-dimethoxytrityl chloride, pyridine, room temperature, 8 hours; c) 2-cyanoethyl N,N,N,N-tetraisopropylphosphane, tetrazole, dichloromethane, room temperature, 3 hours.