[CH3:1][O:2][C:3]([C:5]1[C:14](=[O:15])[NH:13][C:8]2=[N:9][CH:10]=[CH:11][N:12]=[C:7]2[C:6]=1[O:16][C:17](=[O:21])[CH:18]([CH3:20])[CH3:19])=[O:4].[C:22](=O)([O-])[O-].[K+].[K+].CI>C(#N)C.C(OCC)(=O)C.O>[CH3:1][O:2][C:3]([C:5]1[C:14](=[O:15])[N:13]([CH3:22])[C:8]2=[N:9][CH:10]=[CH:11][N:12]=[C:7]2[C:6]=1[O:16][C:17](=[O:21])[CH:18]([CH3:19])[CH3:20])=[O:4]
To a suspension of 8-isobutyryloxy-6-oxo-5,6-dihydro-pyrido[2,3-b]pyrazine-7-carboxylic acid methyl ester (0.422 g) (Example 7.2) in acetonitrile (12 ml) was added potassium carbonate (0.401 g) followed by methyl iodide (0.30 ml). The reaction mixture was heated to 100° C. for 10 minutes in a microwave, and then cooled to ambient temperature. The reaction mixture was diluted with ethyl acetate and water. The phases were separated. The organic phase was washed with water and brine, dried over magnesium sulfate and concentrated. The residue was purified by column chromatography on silica gel (eluent: ethyl acetate/hexane 1:2 to 1:1) to give 8-isobutyryloxy-5-methyl-6-oxo-5,6-dihydro-pyrido[2,3-b]pyrazine-7-carboxylic acid methyl ester as an orange oil (0.418 g). 1H-NMR (400 MHz, CDCl3): 1.36 (d, 6H), 2.95 (sept, 1H), 3.79 (s, 3H), 3.94 (s, 3H), 8.49 (d, 1H), 8.59 (d, 1H) ppm.
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