Enantimer-Differentiating Ability of Cyclo(Phe-Pro)₄ for Noradrenaline Hydrochloride and Preparation of Complexes with Various Amine Hydrochlorides

Abstract

Cyclo(Phe-Pro)₄ (1) formed a 1 : 1 complex with noradrenaline hydrochloride (NAd·HCl) through intermolecular hydrogen bonds and a hydrophobic effects. The formation constant of the 1 : 1 complex of 1 with l-Nad·HCl was approximately 12.3 times that of the complex with d-Nad·HCl. It was presumed that the secondary hydroxy group of l-NAd·HCl formed an intermolecular hydrogen bond with Pro¹ CO of 1, whereas that of d-NAd·HCl did not. The 1 : 1 complexes of 1 with various amine hydrochlorides were prepared.