Acta Crystallographica Section C

Volume 68, Part 1 (January 2012)


organic compounds



sk3425 scheme

Acta Cryst. (2012). C68, o28-o32    [ doi:10.1107/S0108270111052012 ]

Tizanidine and tizanidine hydrochloride: on the correct tautomeric form of tizanidine

S. L. Bekö, S. D. Thoms, M. U. Schmidt and M. Bolte

Abstract: A crystallization series of tizanidine hydrochloride, used as a muscle relaxant for spasticity acting centrally as an [alpha]2-adrenergic agonist, yielded single crystals of the free base and the hydrochloride salt. The crystal structures of tizanidine [systematic name: 5-chloro-N-(imidazolidin-2-ylidene)-2,1,3-benzothiadiazol-4-amine], C9H8ClN5S, (I), and tizanidine hydrochloride {systematic name: 2-[(5-chloro-2,1,3-benzothiadiazol-4-yl)amino]imidazolidinium chloride}, C9H9ClN5S+·Cl-, (II), have been determined. Tizanidine crystallizes with two almost identical molecules in the asymmetric unit (r.m.s. deviation = 0.179 Å for all non-H atoms). The molecules are connected by N-H...N hydrogen bonds forming chains running along [2\overline{1}1]. The present structure determination corrects the structure determination of tizanidine by John et al. [Acta Cryst. (2011), E67, o838-o839], which shows an incorrect tautomeric form. Tizanidine does not crystallize as the usually drawn 2-amino-imidazoline tautomer, but as the 2-imino-imidazolidine tautomer. This tautomer is present in solution as well, as shown by 1H NMR analysis. In tizanidine hydrochloride, cations and anions are connected by N-H...Cl hydrogen bonds to form layers parallel to (100).

Formula: C9H8ClN5S and C9H9ClN5S+·Cl-


cmldisplay filedownload file

Chemical Markup Language (CML) file (4.2 kbytes)
[ doi:10.1107/S0108270111052012/sk3425Isup4.cml ]
Supplementary material


cmldisplay filedownload file

Chemical Markup Language (CML) file (4.8 kbytes)
[ doi:10.1107/S0108270111052012/sk3425IIsup5.cml ]
Supplementary material


Notes:

To open or display or play some files, you may need to set your browser up to use the appropriate software. See the full list of file types for an explanation of the different file types and their related mime types and, where available links to sites from where the appropriate software may be obtained.

The download button will force most browsers to prompt for a file name to store the data on your hard disk.

Where possible, images are represented by thumbnails.

 bibliographic record in  format

  Find reference:   Volume   Page   
  Search:     From   to      Advanced search

Copyright © International Union of Crystallography
IUCr Webmaster