[CH3:1][C:2]1[C:3](=O)[NH:4][C:5](=[O:17])[N:6]([CH:16]=1)[C@@H]1O[C@H](CO)[C@@H](O)[C@H]1O.C1(OC(=O)OC2C=CC=CC=2)C=CC=CC=1.C(=O)(O)[O-].[Na+].C(=O)=O.C[N:44](C=O)C>>[CH3:1][C:2]1[C:3]([NH2:44])=[N:4][C:5](=[O:17])[NH:6][CH:16]=15-Methyluridine (ribosylthymine, commercially available through Yamasa, Choshi, Japan) (72.0 g, 0.279 M), diphenylcarbonate (90.0 g, 0.420 M) and sodium bicarbonate (2.0 g, 0.024 M) were added to DMF (300 mL). The mixture was heated to reflux, with stirring, allowing the evolved carbon dioxide gas to be released in a controlled manner. After 1 hour, the slightly darkened solution was concentrated under reduced pressure. The resulting syrup was poured into diethylether (2.5 L), with stirring. The product formed a gum. The ether was decanted and the residue was dissolved in a minimum amount of methanol (ca. 400 mL). The solution was poured into fresh ether (2.5 L) to yield a stiff gum. The ether was decanted and the gum was dried in a vacuum oven (60° C. at 1 mm Hg for 24 h) to give a solid which was crushed to a light tan powder (57 g, 85% crude yield). The material was used as is for further reactions.
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