[CH3:1][C:2]1[C:3](=[O:18])[NH:4][C:5](=[O:17])[N:6]([CH:16]=1)[C@@H:7]1[O:15][C@H:12]([CH2:13][OH:14])[C@@H:10]([OH:11])[C@H:8]1O.C(=O)(OC1C=CC=CC=1)OC1C=CC=CC=1.C(=O)=O.CCOC(C)=O>CN(C)P(N(C)C)(N(C)C)=O.C(=O)(O)[O-].[Na+]>[CH3:1][C:2]1[C:3](=[O:18])[N:4]=[C:5]2[N:6]([C@@H:7]3[O:15][C@H:12]([CH2:13][OH:14])[C@@H:10]([OH:11])[C@@H:8]3[O:17]2)[CH:16]=1A mixture of 5-methyluridine (16.77 g, 69.2 mmol), diphenyl carbonate (17.8 g, 83.1 mmol) and sodium bicarbonate (100 mg) in hexamethylphosphoramide (175 ml) was heated to 150° C. with stirring until evolution of CO2 ceased (approximately 1 hr). The reaction mixture was cooled and then poured into diethylether (11) while stirring to furnish a brown gum. Repeated washings with diethylether (4×250 ml) furnished a straw colored hygroscopic powder. The solid was purified by short column chromatography on silica gel (400 g). Pooling and concentration of appropriate fractions, which were eluted with CH2Cl2 -MeOH (85:15, v/v) furnished the title compound as a straw colored solid (12 g, 77.3%) which crystallized from EtOH as long needles, m.p. 226°-227° C.
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