title: Physical and crystallographic characterisation of the mGlu5 antagonist MTEP and its monohydrochloride.
abstract: An improved medium scale synthesis of 3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine (MTEP), a selective and potent metabotropic glutamate subtype 5 (mGlu5) antagonist, has allowed thorough characterisation of the crystal structures of the free base and the previously unreported hydrochloride (MTEP.HCl). Hirshfeld surface analysis has revealed that molecules in crystalline MTEP are weakly polar, and aggregate through nonclassical C--H...N hydrogen bonds. A strong ionic N--H(+)...Cl(-) hydrogen bond dominates the crystal packing in MTEP.HCl. Despite significant differences in the crystal packing, the molecular structures of MTEP and MTEP.HCl are very similar. The acid dissociation constants for MTEP were investigated using (1)H NMR spectroscopy. The second acid dissociation constant (pK(a2)), associated with the pyridine nitrogen, was determined to be 3.40 +/- 0.01, whilst pK(a1), associated with the thiazole nitrogen, was estimated to be 0.2. The low pK(a) values make it unlikely that MTEP is protonated in its biologically active form.
authors.affiliation: School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McIldowie
authors.forename: Michael N
authors.initials: MN
authors.lastname: Gandy
authors.forename: Brian W
authors.initials: BW
authors.lastname: Skelton
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Brotchie
authors.forename: George A
authors.initials: GA
authors.lastname: Koutsantonis
authors.forename: Mark A
authors.initials: MA
authors.lastname: Spackman
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Piggott
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors*; D012995:Solubility; D013844:Thiazoles / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: C472365:3-((2-methyl-1,3-thiazol-4-yl)ethynyl)pyridine; D011725:Pyridines; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D013844:Thiazoles