[NH:1]([C:3]1[C:4]2[C:14](=O)[CH:13]([C:16]([O:18]CC)=[O:17])[CH2:12][N:11]([C:21]3[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=3)[C:5]=2[N:6]=[C:7]([S:9][CH3:10])[N:8]=1)[NH2:2].[OH-].[Na+]>C(O)C>[CH3:10][S:9][C:7]1[N:6]=[C:5]2[C:4]3[C:14](=[N:2][NH:1][C:3]=3[N:8]=1)[CH:13]([C:16]([OH:18])=[O:17])[CH2:12][N:11]2[C:21]1[CH:26]=[CH:25][CH:24]=[CH:23][CH:22]=1Crude ethyl 4-hydrazinyl-2-(methylthio)-5-oxo-8-phenyl-5,6,7,8-tetrahydropyrido[2,3-d]pyrimidine-6-carboxylate (20 g), was dissolved in ethanol (300 mL). Aqueous sodium hydroxide (300 mL) (22.52 g, 563 mmol) was added. The reaction mixture was warmed to 60° C. and stirred for 3 h. Upon completion of the reaction (TLC, LCMS), ethanol was removed under reduced pressure and the aqueous layer was acidified using 10% citric acid. The aqueous layer was then extracted with dichloromethane (200 mL×3). The combined organic layers were washed with water (500 mL), dried over anhydrous sodium sulphate, filtered and concentrated under reduced pressure to give crude 7-(methylthio)-5-phenyl-1,3,4,5-tetrahydro-1,2,5,6,8-pentaazaacenaphthylene-3-carboxylic acid (20 g). The crude product was used for decarboxylation in the next step without purification. LCMS [M+H]: 328
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