title: A 1H nmr study of the amide-bond conformational equilibrium in pirenzepine.
abstract: The hindered rotation about the exocyclic amide bond of pirenzepine has been studied using 1H nuclear magnetic resonance spectroscopy. The ratios of the two slowly interconverting conformations (1:1.76 at 2 degrees C and 1:2.37 at 30 degrees C) and the rate of interconversion (1 +/- 0.5 s-1 at 20 degrees C and 247 +/- 20 s-1 at 80 degrees C with delta g ++80 = 71 KJ mol-1) have been measured at various temperatures. The observed rapid rates of interconversion allow us to eliminate the rate of conformational selection of forms II and III as a major contributor to the slow phase of the binding kinetics observed when pirenzepine binds to muscarinic receptors from rat brain (Stockton, Birdsall, Hulme and Burgen, unpublished results).
mesh_terms: D000577:Amides / Q000032:analysis; D001570:Benzodiazepinones / Q000032:analysis*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D010890:Pirenzepine; D011522:Protons; D013237:Stereoisomerism; D013696:Temperature
chemical_list: D000577:Amides; D001570:Benzodiazepinones; D011522:Protons; D010890:Pirenzepine