Hydroxybenzoic acid can not only synthesize Nipagin ester as a preservative, but also be used as the basic raw material of a variety of pharmaceutical products.                                                              

a. Febuxostat
Febuxostat is a new generation of xanthine oxidase inhibitor, which is used in the treatment of hyperuricemia (gout) clinically.
Synthesis of febuxostat: the key intermediate methyl 3-bromo-4 - (2-methylpropoxy) benzoate was obtained from methyl p-hydroxybenzoate by Bromination and etherification, and then reacted with cuprous cyanide to introduce cyano group, and then to synthesize thiazole ring. Finally, febuxostat was obtained by hydrolysis, or thiazole ring was synthesized first, then cyano group was introduced, and then febuxostat was obtained by hydrolysis.
b. Fenofibrate
Fenofibrate is the second generation of phenoxyaryl acid drugs, which can significantly reduce triglyceride (TG), moderately reduce total cholesterol and low-density lipoprotein cholesterol, and can increase high-density lipoprotein cholesterol. It has a good lipid-lowering effect, so it has been widely used in clinical practice. It was listed in the United States by Abbott in 1998.
The synthesis of fenofibrate: 4-hydroxy-4 '- chlorobenzophenone was prepared by chlorination of p-hydroxybenzoic acid with thionyl chloride, and then reacted with 2-bromo-2-methylisopropyl ester to give fenofibrate.
c. Gabexate mesylate
Gabexate mesylate is a non peptide protease inhibitor, which can inhibit the activities of trypsin, kallikrein, fibrinolytic enzyme, thrombin and other proteases, so as to stop the pathology caused by these enzymes. Gabexate mesylate can be used in the treatment of acute mild (edematous) pancreatitis and the adjuvant treatment of acute hemorrhagic necrotizing pancreatitis. It was listed in Japan by Ono pharmaceutical company in 1978.
Synthesis of gabexate mesylate: 6-aminohexanoic acid reacted with S-methylisothiourea sulfate to obtain 6-guanylhexanoic acid hydrochloride, and reacted with diethyl 4,4 '- (sulfinyldioxy) dibenzoate obtained by condensation of ethyl p-hydroxybenzoate with thionyl chloride to obtain gabexate hydrochloride, and then reacted with methanesulfonic acid to obtain gabexate mesylate.
d. Nitidophenitrile
Nitinofenitrile is a kind of veterinary drug, which can block the oxidative carbonation of the worm, reduce the concentration of ATP, and reduce the energy required for cell division, resulting in the death of the worm.
Synthesis of nitinofenitrile: p-hydroxybenzonitrile was prepared from p-hydroxybenzoic acid, urea, aminosulfonic acid and p-cresol, followed by heating reaction, filtration, washing and vacuum distillation of filtrate. 3-nitro-4-hydroxybenzonitrile was synthesized by the reaction of p-hydroxybenzonitrile with concentrated nitric acid in glacial acetic acid, and then reacted with iodine and hydrogen peroxide in acidic ethanol solution to synthesize nitinophenitrile.
e. Nifurat
Nifurat is a broad-spectrum antibacterial drug, which can prevent and cure intestinal or urinary system diseases caused by Escherichia coli, Salmonella, Pasteurella (including Riemerella), aerogenes, proteus, necrotizing bacilli and Staphylococcus. It can be used to treat intestinal and systemic diseases caused by bacteria, Vibrio and fungi in aquatic animals, coccidiosis in chickens, and leukocytosis White crown disease and cecal hepatitis.
The synthesis of nifurate: p-hydroxybenzoate was esterified with p-hydroxybenzoic acid to form methyl p-hydroxybenzoate, then reacted with hydrazine to form p-hydroxybenzoyl hydrazide, and then nitrofurazide was prepared by 5-nitrofurfural reaction.