N[C@H](C(O)=O)CCSC.C[O:11][C:12]1[CH:13]=[CH:14][C:15]2[C:24]3[CH:19]([CH2:20][C:21](=[O:31])[N:22]([C:25]4[CH:30]=[CH:29][CH:28]=[CH:27][N:26]=4)[N:23]=3)[CH2:18][CH2:17][C:16]=2[CH:32]=1.C(=O)([O-])[O-].[K+].[K+]>CS(O)(=O)=O>[OH:11][C:12]1[CH:13]=[CH:14][C:15]2[C:24]3[CH:19]([CH2:20][C:21](=[O:31])[N:22]([C:25]4[CH:30]=[CH:29][CH:28]=[CH:27][N:26]=4)[N:23]=3)[CH2:18][CH2:17][C:16]=2[CH:32]=1A mixture of 1.0 g of methionine, 70 ml of methanesulfonic acid and 10 g of 8-methoxy-2-(2-pyridyl)-4,4a,5,6-tetrahydrobenzo[h]cinnolin-3(2H)-one is stirred at 55° C. for 26 hours. The reaction mixture is poured into ice-water, and the mixture is neutralized with potassium carbonate and extracted with chloroform. The extract is washed with an aqueous solution of sodium chloride and dried over magnesium sulfate. After the solvent is distilled off under reduced pressure, the residue is purified by silica gel chromatography (chloroform:methanol =10:1) and recrystallized from chloroform methanol to give 2.7 g of 8-hydroxy-2-(2-pyridyl)-4,4a,5,6-tetrahydrobenzo[h]cinnolin-3(2H)-one as white crystals, m.p. 193°-194° C.
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