3′-Amino-2′-hydroxy-biphenyl-3-carboxylic acid hydrobromide 1f (285 mg, 0.92 mmol) was dissolved in 3.1 mL of hydrochloric acid (1 N) upon cooling by an ice-water bath, followed by dropwise addition of 1.2 mL of aqueous sodium nitrite (70 mg, 1.01 mmol). After the mixture was stirred for 20 minutes, 2-(3-ethyl-indan-5-yl)-5-methyl-2,4-dihydro-pyrazol-3-one 41d (200 mg, 0.83 mmol) was added. The mixture was adjusted to pH 8 with saturated aqueous sodium bicarbonate followed by addition of 2 mL of ethanol. The reaction mixture was warmed up to room temperature overnight. The reaction was monitored by TLC until the disappearance of the starting materials. The mixture was filtered and the filter cake was added to 20 mL of water. The mixture was adjusted to pH 3˜4 with concentrated hydrochloric acid. The mixture was filtered and the filter cake was dried to obtain the title compound 3′-{N′-[1-(3-ethyl-indan-5-yl)-3-methyl-5-oxo-1,5-dihydro-pyrazol-4-ylidene]-hydrazino}-2′-hydroxy-biphenyl-3-carboxylic acid 41 (145 mg, yield 36.4%) as a red solid.
