Pure and Applied Chemistry

Abstract: Structure­activity relationships are rarely straightforward, and often are more complicated than they appear. For this reason, the use of site-directed mutagenesis as a complementary tool to analyze structure­activity relationships has been invaluable. Here, we illustrate how site-directed mutagenesis has led to greater insight into the molecular basis for molecular recognition of norbinaltorphimine and to the design of novel kappa antagonists. Given the paucity of high-resolution crystal structures for membrane-bound receptors, the use of a coordinated "two-dimensional" paradigm that involves molecular modification of both the ligand and the receptor, affords a useful approach to the study of molecular recognition. This paradigm has led to the design of highly potent and selective kappa opioid receptor antagonists that are derivatives of the delta opioid receptor antagonist, naltrindole.