title: On the structure-activity relationship of histamine H2-receptor antagonists based on the X-ray crystal structures and 1H-NMR spectra of amidine derivatives.
abstract: The conformation of six amidine compounds, which possess a common 3-[(4-thiazolyl)methylthio]propionylamidine framework but exhibit different activities as histamine H2-receptor antagonists, have been subjected to both single crystal X-ray structural and 1H-NMR analyses. The X-ray studies suggest a correlation between antagonist activity and the relative spatial orientation of the thiazolyl and amidine nitrogen atoms. This correlation is supported by a comparison of the conformations observed for the amidines with those of other H2-receptor antagonists and reveal that a folded conformation, specifically the NH...N intramolecular hydrogen-bonded configuration, is important for antagonist activity. The 1H-NMR measurements on the active amidine compounds show that the intramolecular NH...N bond is likely to be present in solution.
mesh_terms: D000578:Amidines; D006635:Histamine H2 Antagonists; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D000578:Amidines; D006635:Histamine H2 Antagonists