Investigation of the N-Substituent Conformation Governing Potency and μ Receptor Subtype-Selectivity in (+)-(3<i>R</i>,4<i>R</i>)-Dimethyl-4-(3-hydroxyphenyl)- piperidine Opioid Antagonists
作者:James B. Thomas、S. Wayne Mascarella、Richard B. Rothman、John S. Partilla、Heng Xu、Karen B. McCullough、Christina M. Dersch、Buddy E. Cantrell、Dennis M. Zimmerman、F. Ivy Carroll
DOI:10.1021/jm980063g
日期:1998.5.1
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) (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 [S-35]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.