Hydrochloric Acid → 4-[[1-[1-(4-tert-butylphenyl)-3-methyl-5-oxopyrazol-4-ylidene]ethylamino]carbamoyl]benzoic acid

To 23.2 mg (0.05 mmol) of the 4-methoxycarbonylbenzoic N′-(1-(1-(4-tert-butylphenyl)-3-methyl-5-oxo-1,5-dihydropyrazol-4-ylidene)-ethyl)-hydrazide synthesized in Synthetic Example 4 in 2.0 ml of methanol, 255 μl (0.255 mmol) of 1M aqueous sodium hydroxide was added at room temperature, and the mixture was heated at from 60° C. to 80° C. for 3.5 hours. After it was cooled to room temperature, 255 μl of 1M hydrochloric acid was added, and the precipitated solid was collected by filtration to obtain 13.9 mg of the desired product as a pale brown solid (yield 61%).