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. 2003 Dec 15;31(24):7175–7188. doi: 10.1093/nar/gkh154

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graphic file with name gkh154s2.jpg — Scheme 2. Conditions: (a) N,N-di-t-butylformamide dimethyl acetal, DMF, room temperature, 3 h; (b) diphenylcarbamoyl chloride, i-Pr₂NEt, room temperature, 2 h, 97% (two steps); (c) TBAF, THF, 0°C–room temperature, 1 h, 87%; (d) DMTrCl, pyridine, room temperature, 1 h, 82%; (e) 2-cyanoethyl N,N-diisopropylchlorophosphoramidite, i-Pr₂NEt, CH₂Cl₂, room temperature, 20 min, 90%.

graphic file with name gkh154s3.jpg — Scheme 2. Conditions: (a) N,N-di-t-butylformamide dimethyl acetal, DMF, room temperature, 3 h; (b) diphenylcarbamoyl chloride, i-Pr₂NEt, room temperature, 2 h, 97% (two steps); (c) TBAF, THF, 0°C–room temperature, 1 h, 87%; (d) DMTrCl, pyridine, room temperature, 1 h, 82%; (e) 2-cyanoethyl N,N-diisopropylchlorophosphoramidite, i-Pr₂NEt, CH₂Cl₂, room temperature, 20 min, 90%.