Stereochemical aspects of benzodiazepine binding to human serum albumin. I. Enantioselective high performance liquid affinity chromatographic examination of chiral and achiral binding interactions between 1,4-benzodiazepines and human serum albumin.

The displacement of a series of 1,4-benzodiazepine (BDZ) drugs from a chiral stationary phase, based upon human serum albumin, for high performance liquid chromatography was investigated. The different displacement patterns obtained using various mobile phase additives could not be interpreted in terms of binding of the solutes to a single site. The observations were better described by considering the attachment of the BDZs to several loci on the protein. Two main mechanisms of binding were discerned, a nonstereoselective mode, which affected all solutes and seemed to occur at a large number of locations on the protein, and a highly stereoselective mode, which involved only one enantiomer of chiral BDZs and presumably one conformation of certain achiral solutes. The stereoselective binding mode encompassed at least four different sites, each of which displayed slightly different structural requirements. It is suggested that the nomenclature currently used to describe drug binding to human serum albumin may be misleading. Rather than the use of site I or site II, it may be preferable to adopt the terms type I and type II binding, according to the displacement patterns of the compound concerned. This approach would retain the conceptual simplicity of the current notation, while avoiding misleading implications of the exact molecular locus of binding.