Clinical data
ATC code None
CAS Number 442-52-4
PubChem (CID) 2782
ChemSpider 2680
UNII T97CB3796L YesY
KEGG D01705
NIAID ChemDB 033090
ECHA InfoCard 100.006.486
Chemical and physical data
Formula C19H20ClN3
Molar mass 325.84 g/mol
3D model (Jmol) Interactive image

Clemizole is an H1 antagonist.


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:[1][2]

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


  1. Jerchel, D.; Fischer, H.; Kracht, M. (1952). "Zur Darstellung der Benzimidazole". Justus Liebigs Annalen der Chemie. 575 (2): 162. doi:10.1002/jlac.19525750204.
  2. GB 703272; M. Schenck, W. Heinz, U.S. Patent 2,689,853 (both 1954 to Schering AG).
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