[OH:1][C:2]1[C:3](=[O:17])[NH:4][C:5](=[O:16])[N:6]([CH:15]=1)[C@@H:7]1[O:14][C@H:11]([CH2:12][OH:13])[C@@H:9]([OH:10])[CH2:8]1.[OH-].[Na+].[CH2:20](Br)[CH3:21]>CO.O>[CH2:20]([O:1][C:2]1[C:3](=[O:17])[NH:4][C:5](=[O:16])[N:6]([CH:15]=1)[C@@H:7]1[O:14][C@H:11]([CH2:12][OH:13])[C@@H:9]([OH:10])[CH2:8]1)[CH3:21]The 2'-deoxy-5-hydroxyuridine (244 mg.,1 mmol) was suspended in a mixture of methanol (10 ml) and water (5 ml) at room temperature, and 1 ml of 1.0N sodium hydroxide solution (1 mmol) was added to generate the monoanion. Ethyl bromide (0.312 ml, 4 mmol) was added, and the reaction mixture was stirred for 16 hours. The solvent was removed in vacuo, and ethanol was added to and evaporated from the residue. The desired 5-ethoxy product was separated from small amounts of the 3-ethyl-5-ethoxy dialkyl byproduct by chromatography on a silica gel column using chloroform-methanol (9:1, v/v) as the solvent. Following crystallization from absolute ethanol, 5-ethoxy-2'-deoxyuridine was obtained in 52% yield (140mg); mp 179°-181° C.; 1H NMR (methyl sulfoxide-d6),δ6 11.38 (1H, br s, NH), 7.58 (1H, s, H-6), 6.18 (1H, t, H-1'), 5.19 (1H, d, 3'-OH), 5.09 (1H, t, 5'-OH), 4.25 (1H, m, H-3'), 3.79 (3H, m. H4' and OCH2CH3), 3.59 (2H, br s,H-5' and H-5"), 2.10 (2H, m, H-2' and H-2") and 1.23 ppm (3H, t, OCH2CH3).
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