C(NC1C=CN([C@@H]2O[C@H](CO)[C@@H](O)[C@H]2O)C(=O)N=1)(=O)C1C=CC=CC=1.[NH:26]1[C-:30]=[N:29][N:28]=[N:27]1.P([O-])([O-])[O-].[NH:35]1[C:39]2[CH:40]=[CH:41][CH:42]=[C-:43][C:38]=2[N:37]=[N:36]1>C(#N)C>[NH:26]1[CH:30]=[N:29][N:28]=[N:27]1.[NH:35]1[C:39]2[CH:40]=[CH:41][CH:42]=[CH:43][C:38]=2[N:37]=[N:36]1N-Benzoylcytidine linked from the 3' hydroxyl group via a hemisuccinate bridge to aminopropyl-substituted HPLC-grade silica (Vydac) was used as the solid-phase support. Samples (100 mg each; 10 micromoles) were shaken in sealed test tubes in acetonitrile (1 ml) with each of the four 5'-dimethoxytrityl-deoxynucleoside-3'-dimethylaminophosphoramidites and either tetrazole (1 mmole) or benzotriazole (600 micromoles) to form the tetrazolide or benzotriazolide-phosphite active species, the latter being a compound of this invention. After thorough washing by repeated centrifugation and subsequent decanting, and oxidation with 0.01M iodine, the support was treated with 2.75% (w/v) trichloroacetic acid in methylene chloride (10 ml) for 5 minutes. Spectrophotometric assay of the dimethoxytrityl carbonium ion produced in the supernatant demonstrated that all couplings had proceeded to greater than 95% of theoretical yield.
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