Synthesis and evaluation of 4-(N,N-diarylamino)piperidines with high selectivity to the δ-opioid receptor: A combined 3D-QSAR and ligand docking study

A series of 4-(N,N-diarylamino)piperidines are synthesized and evaluated for high affinity binding and selectivity to the δ-opioid receptor using a combination of 3D-QSAR and molecular docking techniques. Based on experimental ligand binding data to both μ- and δ- opioid receptors, CoMFA fields are generated and applied to identify potential ligand modifications to further optimize lead compounds. Molecular docking experiments to the δ-receptor are also reported that explain the CoMFA trends predicted as well as the differential binding and selectivity displayed by various compounds in the series. An analysis of the binding site model proposed indicates the piperidines take advantage of 3 key sites or binding domains within the δ-receptor. These include an aromatic pocket (approximately 1/3 into the receptor cavity), an aspartic acid residue (which serves as a docking point for the piperidinyl cationic amine) and a hydrophobic pocket at the extracellular boundary of the receptor cavity. Links are established between ligand modification and amino acid composition at these sites in μ and δ, providing new insight to the structural basis to binding and selectivity across the series and for related piperazines (i.e. SNC80 and BW373U86). Results are also presented that indicate δ- and μ- selectivity may be determined at alternate sites, suggesting opioid receptors may display multiple binding domains. The model is further supported by comparisons with opiate binding modes and site directed mutagenesis studies and is finally applied to suggest new strategies in ligand design.