[NH2:1][C:2]1[CH:10]=[CH:9][C:8]([CH3:11])=[CH:7][C:3]=1[C:4]([OH:6])=O.C([N:14]([CH2:17][CH3:18])CC)C.[C:19](Cl)(=O)[CH2:20][CH2:21]CC.CCOC(C)=O.CCCCCC>CN(C=O)C.CN(C1C=CN=CC=1)C>[CH2:18]([C:17]1[NH:1][C:2]2[C:3]([C:4](=[O:6])[N:14]=1)=[CH:7][C:8]([CH3:11])=[CH:9][CH:10]=2)[CH2:19][CH2:20][CH3:21]
To a solution of 3.0 g (20 mmol) of 2-amino-5-methyl benzoic acid in 20 mL of dry DMF at 0° C. was added 200 mg of DMAP followed by 6.07 g (60 mmol) of triethylamine and 5.02 g (40 mmol) of valeryl chloride. The resulting mixture was stirred at 0° C. for 30 min. The mixture was heated to 110° C. and monitored by TLC for the formation of the intermediate quinoxazolone (Rf =0.8, 40% EtOAc/hexane). Following complete formation of the intermediate 10 g (100 mmol) of (NH4)2CO3 was added cautiously. Heating was continued to ensure consumption of the quinoxazolone and formation of the polar (Rf =0.4, 40% EtOAc/hexane) quinazolin-4(1H)-one. The reaction mixture was concentrated in vacuo and the residue was taken up in 50 mL of ether and 50 mL of water. The mixture was filtered and the filtrate discarded after washing the residue with 20 mL of ether. The residue was recrystalized from MeOH to give 1.07 g (25%) of the title compound as a white crystalline solid.
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