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-Formamide-1-(2-Formyloxyethyl) Pyrazole manufacturers and is a valuable source of guidance and direction for companies and individuals interested in the industry. Firstly, the report ...
Targeted News Service (subscription)
Wed, 31 Dec 2014 11:30:00 -0800
31 -- Merial, Duluth, Georgia, has been assigned a patent (8,921,408) developed by seven co-inventors for "compositions comprising an aryl pyrazole and/or a formamidine, methods and uses thereof." The co-inventors are Mark David Soll, Alpharetta, ...
Targeted News Service (subscription)
Fri, 02 Jan 2015 11:30:00 -0800
2 -- MUSC Foundation for Research Development, Charleston, South Carolina, has been assigned a patent (8,921,401) developed by four co-inventors for "pyrazole compounds, compositions and methods for treatment of degenerative diseases and ...
Sun, 04 Jan 2015 23:44:38 -0800
我们发现了一种构建三氟甲基吡唑（Trifluoromethyl pyrazole）的方法，这可以用于治疗艾滋病或关节炎，”他说。 华大基因研究院（BGI）. 华大基因研究院共发表了51篇论文（WFC=15.3），其中7篇发表在Nature和Science杂志上 ...
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 ...
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, 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 ...
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