title: Investigation of the N-substituent conformation governing potency and mu receptor subtype-selectivity in (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonists.
abstract: A study of the binding site requirements associated with the N-substituent of (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) derivatives was undertaken using a set of rigid vs flexible N-substituents. The study showed that compounds 7-9 bearing the trans-cinnamyl N-substituent most closely reproduced the potency at the opioid receptor of the flexible N-propylphenyl or N-propylcyclohexyl analogues previously reported. Neither the N-substituted cis-cinnamyl nor the cis-phenylcyclopropylmethyl compounds 10 and 11, respectively, showed high affinity for the opioid receptor. However, the N-trans-phenylcyclopropylmethyl compound 12 closely approximated the affinity of compounds 7-9. Additionally, we found that free rotation of the phenyl ring is necessary for high affinity binding and mu receptor subtype selectivity as the planar N-substituted thianaphthylmethyl and benzofuranylmethyl compounds 13 and 14 had significantly lower binding affinities. Altogether, these findings suggest that the high binding affinity, selectivity, and antagonist potency of N-propylphenyl or N-propylcyclohexyl analogues of (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) are achieved via a conformation wherein the connecting chain of the N-substituents is extended away from piperidine nitrogen with the appended ring system rotated out-of-plane relative to the connecting chain atoms. This conformation is quite similar to that observed in the solid state for 5, as determined by single crystal X-ray analysis. Additionally, it was found that, unlike naltrexone, N-substituents bearing secondary carbons attached directly to the piperidine nitrogen of 4 suffer dramatic losses of potency vs analogues not substituted in this manner. Using a functional assay which measured stimulation or inhibition of [35S]GTP-gamma-S binding, we show that the trans-cinnamyl analogues of (+)-(3R, 4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (4) retain opioid pure antagonist activity and possess picomolar antagonist potency at the mu receptor.
authors.affiliation: Chemistry and Life Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Thomas
authors.forename: S W
authors.initials: SW
authors.lastname: Mascarella
authors.forename: R B
authors.initials: RB
authors.lastname: Rothman
authors.forename: J S
authors.initials: JS
authors.lastname: Partilla
authors.forename: H
authors.initials: H
authors.lastname: Xu
authors.forename: K B
authors.initials: KB
authors.lastname: McCullough
authors.forename: C M
authors.initials: CM
authors.lastname: Dersch
authors.forename: B E
authors.initials: BE
authors.lastname: Cantrell
authors.forename: D M
authors.initials: DM
authors.lastname: Zimmerman
authors.forename: F I
authors.initials: FI
authors.lastname: Carroll
mesh_terms: D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D018360:Crystallography, X-Ray; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008968:Molecular Conformation; D009292:Narcotic Antagonists / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D010880:Piperidines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D017465:Receptors, Opioid, delta / Q000037:antagonists & inhibitors; D017473:Receptors, Opioid, kappa / Q000037:antagonists & inhibitors; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors*
chemical_list: D009292:Narcotic Antagonists; D010880:Piperidines; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D016244:Guanosine 5'-O-(3-Thiotriphosphate)