[C:1]1([C:7]2[N:12]=[C:11]3[N:13]=[C:14]([NH2:17])[CH:15]=[CH:16][C:10]3=[N:9][CH:8]=2)[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[CH3:18][O:19][NH:20][C:21](=O)[O:22]C1C=CC([N+]([O-])=O)=CC=1>N1C=CC=CC=1>[CH3:18][O:19][NH:20][C:21]([NH:17][C:14]1[CH:15]=[CH:16][C:10]2[C:11]([N:13]=1)=[N:12][C:7]([C:1]1[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1)=[CH:8][N:9]=2)=[O:22]100 mg of 3-phenylpyrido[2,3-b]pyrazin-6-ylamine (0.45 mmol) were dissolved in pyridine and admixed with 191 mg of p-nitrophenyl N-methoxycarbamate (0.90 mmol). The mixture was heated under reflux for 4 h. For workup, the pyridine was removed under reduced pressure, and the residue was partitioned in ethyl acetate and distilled water. The phases were separated and the aqueous phase was extracted twice with ethyl acetate. The combined organic phases were dried over MgSO4 and the solvent was removed under reduced pressure. The residue was purified by column chromatography on silica gel (dichloromethane/methanol eluent). A light beige solid was isolated.
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