The mixture of isobutyryl chloride (160 mg, 1.5 mmol) and ammonium isothiocyanate (114.2 mg, 1.5 mmol) in acetone (2.0 mL) was heated at 40° C. for 3 h. To the above reaction mixture, 3-(5-amino-2-methylphenyl)-1,7-dimethyl-1,6-naphthyridin-2(1H)-one (15) (419 mg, 1.5 mmol) was added at rt and stirred for 30 min. The solvent was removed under vacuum to yield N-(3-(1,7-dimethyl-2-oxo-1,2-dihydro-1,6-naphthyridin-3-yl)-4-methylphenylcarbamothioyl)isobutyramide 22, which was used without purification. MS m/z 409.2 (M+1).
