Michael acceptor approach to the design of new salvinorin A-based high affinity ligands for the kappa-opioid receptor.

Salvinorin A, a compound from the plant Salvia divinorum, binds strongly and selectively to the κ-opioid receptor (KOR). A new series of salvinorin A derivatives with reactive Michael acceptor groups at C-2 was created to explore how the compound interacts with the receptor. Most of these derivatives retained high affinity for KOR, and some also bound to the μ-opioid receptor (MOR). None showed wash-resistant irreversible binding. Using the KOR crystal structure, mutagenesis data, and other methods, the researchers identified possible ways the new compounds interact with both KOR and MOR.

Study at a glance

Abstract

The neoclerodane diterpenoid salvinorin A is a major secondary metabolite isolated from the psychoactive plant Salvia divinorum. Salvinorin A has been shown to have high affinity and selectivity for the κ-opioid receptor (KOR). To study the ligand-receptor interactions that occur between salvinorin A and the KOR, a new series of salvinorin A derivatives bearing potentially reactive Michael acceptor functional groups at C-2 was synthesized and used to probe the salvinorin A binding site. The κ-, δ-, and μ-opioid receptor (KOR, DOR and MOR, respectively) binding affinities and KOR efficacies were measured for the new compounds. Although none showed wash-resistant irreversible binding, most of them showed high affinity for the KOR, and some exhibited dual affinity to KOR and MOR. Molecular modeling techniques based on the recently-determined crystal structure of the KOR combined with results from mutagenesis studies, competitive binding, functional assays and structure-activity relationships, and previous salvinorin A-KOR interaction models were used to identify putative interaction modes of the new compounds with the KOR and MOR.