O[C:2]1[C:10]([NH:11][C:12](=[O:19])[C:13]2[CH:18]=[CH:17][N:16]=[CH:15][CH:14]=2)=[CH:9][CH:8]=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].O.C1(C)C=CC(S(O)(=O)=O)=CC=1.C1(C)C(C)=CC=CC=1.C(=O)([O-])[O-].[K+].[K+]>C(OCC)(=O)C>[N:16]1[CH:15]=[CH:14][C:13]([C:12]2[O:19][C:2]3[C:3]([C:4]([OH:6])=[O:5])=[CH:7][CH:8]=[CH:9][C:10]=3[N:11]=2)=[CH:18][CH:17]=1A mixture of methyl ester of 2-hydroxy-3-isonicotinoylamino-benzoic acid (500 mg, 1.84 mmol), p-toluenesulfonic acid mono-hydrate (349 mg, 1.84 mmol) and xylene (20 ml) was heated under reflux for 14 hrs. and then p-toluenesulfonic acid mono-hydrate (349 mg, 1.84 mmol) was further added and refluxed under heating for 2 hrs. The reaction mixture was cooled with ice, and ethyl acetate and 10% aqueous potassium carbonate solution were added thereto. The organic phase was separated, washed with water and brine in turn and then dried. The solvent was distilled off under reduced pressure, and the residue was triturated with a mixture of n-hexane/diisopropyl ether (4/1), filtered and dried to give methyl ester of [2-(4-pyridyl)-benzoxazol-7-yl]carboxylic acid (382 mg, 82%) as pale yellow crystals.
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