Pyrazolone is 5-memberedheterocycle containing two adjacentnitrogen atoms. It can be viewed as a derivative ofpyrazole possessing an additionalcarbonyl (C=O) group. Compounds containing this functional group are useful commercially inanalgesics and dyes.[1]
Pyrazolone can exist in two isomers: 3-pyrazolone and 4-pyrazolone.
These isomers can interconvert via lactam–lactim and imine–enaminetautomerism; these conversion often displayphotochromism. For pyrazolone derivatives, the 3-pyrazolone isomer can be stabilized withN-alkyl orN-aryl substituents.
The first synthesis of pyrazolones was reported in 1883 byLudwig Knorr, via a condensation reaction betweenethyl acetoacetate andphenylhydrazine.[2]
Many pyrazolones are produced by functionalization of preformed pyrazolones.
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Pyrazolones are amongst the oldest synthetic pharmaceuticals, starting with the introduction ofantipyrine (phenazone) in 1880s.[3][4] The compounds generally act asanalgesics and includedipyrone (Metamizole),aminophenazone,ampyrone,famprofazone,morazone,nifenazone,piperylon andpropyphenazone. Of thesedipyrone (the so-called "Mexican aspirin") is perhaps the most widely used.[3][5]
The basic structure has been also used in a number of newer drugs of other effects.[5]Edaravone is useful for prevention and/or therapy of arterial wall injury.[6]Eltrombopag is used to address low blood platelet count.
Pyrazolone groups are present in several important dyes. They are commonly used in combination withazo groups to give a sub-family of azo dyes; sometimes referred to as azopyrazolones (tartrazine,orange B,mordant red 19,yellow 2G).Acid Yellow 17,Acid Yellow 23 (tartrazine),Pigment Yellow 13, andPigment Red 38 are produced on the multi-ton scale annually.[1]
Pyrazolones have been studied as ligands.[7]
| pyrazolones / pyrazolidines | |
|---|---|
| salicylates | |
| acetic acid derivatives and related substances | |
| oxicams | |
| propionic acid derivatives (profens) |
|
| n-arylanthranilic acids (fenamates) | |
| COX-2 inhibitors (coxibs) | |
| other | |
| NSAID combinations | |
Key:underline indicates initially developed first-in-class compound of specific group;#WHO-Essential Medicines;†withdrawn drugs;‡veterinary use. | |
Authority control databases: National |
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