[CH3:1][O:2][C:3]1[CH:4]=[CH:5][C:6]2[N:11]=[CH:10][C:9](=[O:12])[NH:8][C:7]=2[N:13]=1.I[CH2:15][CH2:16][C@H:17]1[CH2:21][O:20][C:19]([CH3:23])([CH3:22])[O:18]1.C(=O)([O-])[O-].[Cs+].[Cs+].O>CN(C)C=O>[CH3:22][C:19]1([CH3:23])[O:18][C@@H:17]([CH2:16][CH2:15][N:8]2[C:9](=[O:12])[CH:10]=[N:11][C:6]3[CH:5]=[CH:4][C:3]([O:2][CH3:1])=[N:13][C:7]2=3)[CH2:21][O:20]1In N,N-dimethylformamide (400 ml) were dissolved 6-methoxypyrido[2,3-b]pyrazin-3(4H)-one (14.53 g, 82.00 mmol) and (4S)-4-(2-iodoethyl)-2,2-dimethyl-1,3-dioxolane (23.10 g, 90.20 mmol). Cesium carbonate (34.7 g, 1.06.6 mmol) was added to the solution and the mixture was stirred at 50° C. for 11 hours. After cooling in the air, water was added to the reaction solution and the mixture was extracted with ethyl acetate. The extract was washed with saturated sodium chloride solution, dried over anhydrous sodium sulfate and the solvent was removed under reduced pressure. The residue was purified by silica gel column chromatography (hexane/ethyl acetate) to yield 22.58 g (90%) of the title compound in the form of a yellow orange oily product.
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