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Clemizole

Topic: Chemistry

 From HandWiki - Reading time: 10 min

Clemizole, sold under the brand names Allercur and Histacur, is a histamine H1 receptor antagonist of the benzimidazole group described as an antihistamine, antipruritic, and sedative which is no longer marketed.[1][2][3][4] It is a first-generation antihistamine.[5]

It is also a serotonin receptor agonist and is being studied for the potential treatment of Dravet syndrome, Lennox–Gastaut syndrome, and epilepsy under the development code name EPX-100.[6][4][7] The drug is said to act specifically as a serotonin 5-HT2 receptor agonist,[8][9] with prominent affinity for the serotonin 5-HT2A and 5-HT2B receptors having been reported.[5][4] On the other hand, it showed markedly lower affinity for the serotonin 5-HT2C receptor.[4] Clemizole also showed affinity for several other receptors.[4]

The drug was first described in the scientific literature by 1952.[1] Its serotonin receptor agonist and anticonvulsant properties were discovered in 2017.[6][4]

Chemistry

Synthesis

Benzimidazoles substituted with an alkylamine at position 2 have a venerable history as H1 antihistaminic agents. The standard starting material for many benzimidazoles consists of phenylenediamine, or its derivatives.

Clemizole synthesis:[10][11][12]

Reaction of that compound with chloroacetic acid can be rationalized by invoking initial formation of the chloromethyl amide. Imide formation with the remaining free amino group closes the ring to afford 2-chloromethyl benzimidazole (3). Displacement of halogen with pyrrolidine affords the alkylation product. The proton on the fused imidazole nitrogen is then removed by reaction with sodium hydride. Treatment of the resulting anion with α,4-dichlorotoluene gives the H1 antihistaminic agent clemizole (5).

See also

References

  1. ↑ 1.0 1.1 The Dictionary of Drugs: Chemical Data: Chemical Data, Structures and Bibliographies. Springer US. 2014. p. 288. ISBN 978-1-4757-2085-3. https://books.google.com/books?id=0vXTBwAAQBAJ&pg=PA288. Retrieved 29 October 2024. 
  2. ↑ Schweizerischer Apotheker-Verein (2004). Index Nominum: International Drug Directory. Medpharm Scientific Publishers. p. 291. ISBN 978-3-88763-101-7. https://books.google.com/books?id=EgeuA47Ocm4C&pg=PA291. Retrieved 29 October 2024. 
  3. ↑ Concise Dictionary of Pharmacological Agents: Properties and Synonyms. Springer Netherlands. 2012. p. 78. ISBN 978-94-011-4439-1. https://books.google.com/books?id=tsjrCAAAQBAJ&pg=PA78. Retrieved 29 October 2024. 
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 "Clemizole and modulators of serotonin signalling suppress seizures in Dravet syndrome". Brain 140 (3): 669–683. March 2017. doi:10.1093/brain/aww342. PMID 28073790. 
  5. ↑ 5.0 5.1 "Dravet syndrome therapeutics: where are we, what works, and what's next?". Expert Opin Pharmacother 26 (14-15): 1549–1564. 2025. doi:10.1080/14656566.2025.2576608. PMID 41114441. "A first-generation antihistamine from the 1950s, clemizole fell out of use with the advent of newer antihistaminergic drugs [77]. Unexpectedly, it resurfaced as a promising anticonvulsant in a 2013 high-throughput, phenotype-based drug screen [78]. The Baraban group employed a zebrafish model harboring Scn1a haploinsufficiency, displaying seizure-like behaviors and electrographic abnormalities, to screen over 2,300 small molecules. Clemizole emerged as a potent seizure suppressor, acting primarily via serotonergic receptor modulation, notably at 5-HT2A and 5-HT2B subtypes [68].". 
  6. ↑ 6.0 6.1 "Pharmacological diversity amongst approved and emerging antiseizure medications for the treatment of developmental and epileptic encephalopathies". Ther Adv Neurol Disord 16. 2023. doi:10.1177/17562864231191000. PMID 37655228. 
  7. ↑ "Clemizole - Epygenix Therapeutics/University of California at San Francisco". 9 October 2024. https://adisinsight.springer.com/drugs/800049411. 
  8. ↑ Pasculli, Louie (27 March 2026). "EPX-100 Shows Promising Seizure Reduction in Ongoing Open-Label Extension". https://www.neurologylive.com/view/epx-100-shows-promising-seizure-reduction-ongoing-open-label-extension. 
  9. ↑ Amit Ray (8 December 2025). "EPX-100 as Adjunctive Therapy in Patients With Dravet Syndrome: Preliminary Results From the Open-Label Extension Phase of the ARGUS Study". https://aesnet.org/abstractslisting/epx-100-as-adjunctive-therapy-in-patients-with-dravet-syndrome-preliminary-results-from-the-open-label-extension-phase-of-the-argus-study. 
  10. ↑ "Zur Darstellung der Benzimidazole". Justus Liebigs Annalen der Chemie 575 (2): 162–173. 1952. doi:10.1002/jlac.19525750204. 
  11. ↑ Schenck M, Heinz W, GB patent 703272, issued 1954, assigned to Schering AG
  12. ↑ Schenck M, Heinz W, US patent 2689853, issued 1954, assigned to Schering AG



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