A critical structural determinant of opioid receptor interaction with phenolic 5-phenylmorphans

The opioid receptor binding affinities of N-methyl- and N-phenethyl-5-phenylmorphans with a meta-hydroxy substituent 3-(2-methyl-2-azabicyclo3.3.1]non-5-yl)-phenol (1a), and 3-(2-phenethyl-2-azabicyclo3.3.1]non-5-yl)-phenol (1b)] were compared with the affinities of four new ligands bearing an ortho- or para-hydroxyl substituent (2-(2-methyl-2-azabicyclo3.3.1]non-5-yl)-phenol (2a) and 2-(2-phenethyl-2-azabicyclo3.3.1]non-5-yl)-phenol (2b), 4-(2-methyl-2-azabicyclo3.3.1]non-5-yl)-phenol (3a), and 4-(2-phenethyl-2-azabicyclo3.3.1]non-5-yl)-phenol (3b)) that were synthesized from 2-bromoanisole or the known 2-methyl-5-phenyl-2-azabicyclo3.3.1]nonane (13), respectively. The data indicated that either the electronic state of the phenolic ring is critical for the ligand's interaction with an opioid receptor, or that there must be a specific distance and angle for a hydrogen bond between the phenolic moiety and an amino acid in the binding domain that cannot be altered.