Antipodal α-N-(methyl through decyl)-N-normetazocines (5,9α-dimethyl- 2'-hydroxy-6,7-benzomorphans): In vitro and in vivo properties

Article abstract of DOI:10.1021/jm00046a026

The enantiomeric (-)- and (+)-N-(methyl through decyl) normetazocines (5,9α-dimethyl-2'-hydroxy-6,7-benzomorphans) were synthesized and their in vitro and in vivo activities determined. Increasingly bulky enantiomeric N- alkyl homologs were prepared until their interaction with the σ₁ receptor decreased and their insolubility became a hindrance to their evaluation in vivo and/or in vitro. The (-)-methyl, -pentyl, -hexyl, and -heptyl homologs were essentially as potent as, or more potent than, morphine in the tail- flick, phenylquinone, and hot-plate assays for antinociceptive activity; the (-)-propyl homolog had narcotic antagonist activity between that of nalorphine and naloxone in the tail-flick vs morphine assay, and it also displayed antagonist properties in the single-dose suppression assay in the rhesus monkey. The antinociceptively potent (-)-heptyl homolog did not substitute for morphine in monkeys but did show morphine-like properties in a primary physical-dependence study in continuously infused rats. All five potent compounds showed high affinity for the μ opioid receptor from both rat and monkey preparations and the κ opioid receptor (<0.05 μM), and all except the (-)-methyl homolog interacted reasonably well at the δ receptor (K(i) <0.1 μM). The (-)-propyl compound was equipotent (K(i) 1.5-2.0 nM) at μ and κ receptors. The pattern of interaction of the (-)-enantiomeric homologs with μ receptors from rat and monkey preparations was similar, but not identical. The enantioselectivity of the homologs for μ receptors was greater in the rat than in the monkey preparation for all but the N-H and butyl compounds, and the enantioselectivity of the lower homologs (methyl through butyl) for the μ (monkey) receptor was greater than for the κ or δ receptors. However, bulkier homologs (hexyl through decyl) displayed higher enantioselectivity at κ or δ receptors than at the μ (monkey) receptor. The (+)-butyl through (+)-octyl homologs were essentially equipotent with, or more potent than, (+)-pentazocine at the σ receptor. Only the (+)-H and (+)- methyl homologs had high affinity (<0.05 μM) at PCP binding sites.