Pyrazole is the organic compound with the formula C3H3N2H. It is a heterocycle characterized by a 5-membered ring of three carbon atoms and two adjacent nitrogen centres. Pyrazoles are also the class of compounds that have the ring C3N2 with adjacent nitrogen centres. A notable drug containing a pyrazole ring is Celebrex.
Preparation and reactions
Pyrazoles are synthesized by the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation:
Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine. For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole:
- CH3C(O)CH2C(O)CH3 + N2H4 → (CH3)2C3HN2H + 2 H2O
The term pyrazole was given to this class of compounds by German Chemist Ludwig Knorr in 1883. In a classical method developed by German chemist Hans von Pechmann in 1898, pyrazole was synthesized from acetylene and diazomethane.
Conversion to scorpionates
Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate. Pyrazole itself reacts with potassium borohydride at high temperatures (~200 °C) to form a tridentate ligand known as Tp ligand:
- KBH4 + 3 C3H3N2H → KBH(C3H3N2)3 + 3 H2
Occurrence and uses
, a pyrazole derivative used as an analgesic
In medicine, derivatives of pyrazoles are used for their analgesic, anti-inflammatory, antipyretic, antiarrhythmic, tranquilizing, muscle relaxing, psychoanaleptic, anticonvulsant, monoamineoxidase inhibiting, antidiabetic and antibacterial activities.
In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of watermelons
Imidazole is an analog of pyrazole with two non-adjacent nitrogen atoms. In isoxazole, another analog, the nitrogen atom in position 1 replaced by oxygen.
- ^ Eicher, T.; Hauptmann, S. (2003). The Chemistry of Heterocycles: Structure, Reactions, Syntheses, and Applications (2nd ed.). Wiley-VCH. ISBN 3-527-30720-6.
- ^ Review article (properties, biological activities, syntheses of pyrazoles): A. Schmidt, A. Dreger (2011). "Recent Advances in the Chemistry of Pyrazoles. Properties, Biological Activities, and Syntheses". Curr. Org. Chem 15 (9): 1423–1463. doi:10.2174/138527211795378263.
- ^ William S. Johnson and Robert J. Highet (1963), "3,5-Dimethylpyrazole", Org. Synth.; Coll. Vol. 4: 351
- ^ Pyrazol aus Acetylen und Diazomethan H. v. Pechmann Berichte der deutschen chemischen Gesellschaft Volume 31 Issue 3, Pages 2950–51, 1898 doi:10.1002/cber.18980310363
- ^ Fowden; Noe, Ridd and White, (1959). Proc. Chem. SOC.,: 131.
- ^ Noe, F F; L Fowden (1959). "alpha-Amino-beta-(pyrazolyl-N) propionic acid: a new amino-acid from Citrullus vulgaris (water melon)". Nature 184: 69–70. doi:10.1038/184069a0. ISSN 0028-0836.
Business Wire (press release)
Wed, 05 Nov 2014 10:56:15 -0800
The report provides key statistics on the market status of the 5-Amino-1-(2-Hydroxyethyl) Pyrazole manufacturers and is a valuable source of guidance and direction for companies and individuals interested in the industry. Firstly, the report provides a ...
Nashville Post (subscription)
Wed, 03 Dec 2014 10:19:05 -0800
US 8,901,125 entitled SUBSTITUTED BICYCLIC ALKOXY PYRAZOLE ANALOGS AS ALLOSTERIC MODULATORS OF MGLUR5 RECEPTORS invented by P. Jeffrey Conn, Brentwood, TN; Craig W. Lindsley, Brentwood, TN; Shaun R. Stauffer, Brentwood, TN ...
Thu, 27 Nov 2014 08:33:16 -0800
Des amides de pyrazole pourraient fournir de nouveaux traitements antipaludéens. Ces composés dérèglent les concentrations de sodium dans les cellules du parasite, ce qui provoque une entrée massive d'eau, puis le gonflement et l'explosion des cellules ...
Mon, 10 Nov 2014 08:00:25 -0800
The team demonstrated the effectiveness of the technique by using it to modify a wide variety of heterocyclic structures that are frequently present in drug molecules, including furans, benzofurans and benzothiophenes; indole, pyrrole, thiazole ...
Pharmaceutical Technology Magazine
Mon, 10 Nov 2014 19:27:30 -0800
The main structural feature of Taselisib is a seven-membered benzoxazepine core that is substituted with a functionalized pyrazole at one end and an N-isopropyl-3-methyl-1,2,4-triazole heterocycle at the other end. The discovery route to prepare the ...
Fri, 12 Sep 2014 05:08:05 -0700
Pfizer, Inc., is a major American developer of pharmaceutical medications and vaccines for a wide spectrum of medical disciplines. The majority of Pfizer's business is operated in the northeastern United States, where the company has its corporate ...
Fri, 14 Nov 2014 02:53:09 -0800
This structure is held together by a combination of [N–H···N] hydrogen bonds between the terminal pyrazole rings and [π···π] stacking between the electron-rich pyrazoles and electron-poor tetrafluorobenzenes. Such a synergistic arrangement makes this ...
Chemical Watch (subscription)
Thu, 18 Sep 2014 09:07:30 -0700
ipconazole (ISO), expected by 14 November. It will cover the endpoints of reproductive 2; STOT RE 2; acute toxicity 4; aquatic acute 1; and aquatic chronic 1;; 5-fluoro-1,3-dimethyl-N-[2-(4-methylpentan-2-yl)phenyl]-1H-pyrazole-4-carboxamide. Expected ...
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