Muscarinic acetylcholine receptor binding affinities of pethidine analogs.

A series of pethidine analogs were synthesized and their affinities for the [(3)H]N-methyl-scopolamine (NMS) binding site on muscarinic acetylcholine receptors (mAChRs) were determined using M1, M3 or M5 human mAChRs expressed by Chinese hamster ovary (CHO) cell membranes. Compound 6b showed the highest binding affinities at M1, M3 and M5 mAChRs (Ki=0.67, 0.37, and 0.38 µM, respectively).

Synthesis and structure-activity studies of benzyl ester meperidine and normeperidine derivatives as selective serotonin transporter ligands.

A series of benzyl esters of meperidine and normeperidine were synthesized and evaluated for binding affinity at serotonin, dopamine and norepinephrine transporters. The 4-methoxybenzyl ester 8b and 4-nitrobenzyl ester 8c in the meperidine series and 4-methoxybenzyl ester 14a in the normeperidine series exhibited low nanomolar binding affinities at the SERT (K(i) values <2nM) and high SERT selectivity (DAT/SERT >1500 and NET/SERT >1500).

Opioids and efflux transporters. Part 3: P-glycoprotein substrate activity of 3-hydroxyl addition to meperidine analogs.

Numerous studies have shown that many clinically employed opioid analgesics are substrates for P-glycoprotein (P-gp), suggesting that up-regulation of P-gp may contribute to the development of central tolerance to opioids. The studies herein focus on the development of SAR for P-gp substrate activity in the meperidine series of opioids. Addition of a 3-OH to meperidine and the ketone analog of meperidine yielding bemidone and ketobemidone, respectively, significantly increased P-gp substrate affinity. The results of this study have implications in the development of novel analgesics to be utilized as tools to study the contribution of P-gp on the development of central tolerance to opioids.

Structure-activity studies of 3'-4'-dichloro-meperidine analogues at dopamine and serotonin transporters.

The structure-activity relationships of 3',4'-dichloro-meperidine were investigated at dopamine (DAT) and serotonin transporters (SERT). Large ester substituents and lipophilic groups at the 4-position favored molecular recognition at the SERT. The benzyl ester of 3',4'-dichloro-meperidine exhibited high potency and high selectivity for the SERT (DAT/SERT=760). Chemical modification of the ester group and N-substitution generally led to compounds with decreased DAT affinity. Only small esters and alkyl groups were tolerated at the 4-position of the meperidine ring system by the DAT. Overall, the meperidine analogues were generally more selective for the SERT than for the DAT.

Synthesis and biological evaluation of meperidine analogues at monoamine transporters.

A series of aryl-substituted meperidine analogues was synthesized, and the binding affinities were determined at the DAT, SERT, and NET as well as at mu-opioid receptors. Generally the analogues exhibited increased affinity for the DAT and SERT relative to meperidine but exhibited low binding affinity for the NET. The 2-naphthyl derivative 7f was the most potent ligand at the SERT (K(i) = 0.0072 muM) and was the most selective ligand for the SERT over the DAT (DAT/SERT = 158) and mu-opioid receptors (mu/SERT = 281). The 3,4-dichlorophenyl derivative 7e was the most potent ligand at the DAT (K(i) = 0.125 muM) and was the most selective ligand for the DAT over mu-opioid receptors (mu/DAT = 16.3) but remained slightly more selective for the SERT over the DAT(DAT/SERT = 6.68). Three compounds, the 3,4-dichlorophenyl derivative 7e and the 2-naphthyl analogues 6f and 7f, were identified that were more potent at the DAT than meperidine and that exhibited well-defined biphasic dopamine uptake inhibition similar to meperidine. However, none of the analogues tested produced locomotor effects or substituted for cocaine in drug discrimination studies, suggesting that the mu-opioid effects of these analogues may contribute to the poor efficacy observed in vivo.

Synthesis, dopamine and serotonin transporter binding affinities of novel analogues of meperidine.

A series of meperidine analogues was synthesized and the binding affinities for the dopamine and serotonin transporters were determined. The substituents on the phenyl ring greatly influenced the potency and selectivity of these compounds for the transporter binding sites. In general, meperidine (3) and its analogues were more selective for serotonin transporter binding sites and the esters 9 were more potent than the corresponding nitriles 8. The 3,4-dichloro derivative 9e was the most potent ligand of the series for dopamine transporter binding sites while the 2-naphthyl derivative 9g exhibited the most potent binding affinity and was highly selective for serotonin transporter binding sites.

[Synthesis and CNS-activity of spirocyclic pethidine and prodine analogs]. / Synthese und ZNS-Aktivität spirocyclischer Pethidin- und Prodin-Analoga.

The bromoacetals 5a and 5b react with n-butyllithium and the piperidone 7 to yield the hydroxyacetals 8b and 8c, respectively. Cyclization of 8b and 8c followed by acid hydrolysis affords the spirocyclic hemiacetals 10b and 10c which are oxidized by PCC to give the spirocyclic prodine analogues 4b and 4c. The corresponding spirocyclic pethidine derivative 2 is prepared by alkylation of the 2-benzopyran-3-one 16 with N-Lost (17). In the mouse writhing test the spiropethidine 2 is not analgesic active up to a dose of 20 mg/kg body weight (bw). In the spirocyclic prodine series the methylated lactone 4c is the most active analgesic with an ED50-value (ED50 = 9.2 mg/kg bw) in the range of the ED50-value of tramadol.

Opioid properties of some derivatives of pethidine based on tropane.

The preparation of some tropane analogues of pethidine and its reversed ester, chiefly with preferred 3 alpha-m-hydroxyphenyl chair conformations, is described. The former were secured from tropan-3-one in a sequence of reactions involving cyanide attack, hydrolysis, Grignard attack and then rearrangements. The reversed ester was obtained by treating tropan-3-one with lithium phenyl, followed by acylation. Configurational and conformational assignments follow from NMR analysis. The antinociceptive potencies of these compounds in mice are reported, and discussed in relation to non-phenolic congeners and the 4-arylpiperidine moiety of morphine.

Photoaffinity labelling of mitochondrial NADH: ubiquinone reductase with pethidine analogues.

1. Chemically reactive derivatives of pethidine analogues--novel potent inhibitors of the mitochondrial NADH: ubiquinone reductase (complex I)--were synthesized. 2. Dose-response curves of these components revealed that the photoactivatable aryl azido derivative has retained most of the inhibitory activity displayed by the parent substance. After introduction of a radioactive iodine isotope into the molecule, it was used as a probe for the localization of the inhibitor binding polypeptides within complex I. 3. Photolysis of the radiolabelled derivative bound to isolated complex I both from Neurospora crassa and beef heart resulted in a covalent incorporation of the inhibitor into 6-7 individual subunits of the enzyme. Essentially the same labelling patterns were obtained, when whole mitochondrial membranes were incubated with the reactive derivative. 4. Applying a double isotope labelling technique, the inhibitor-binding polypeptides in N. crassa were identified as mitochondrially synthesized constituents of complex I (ND gene products). In the beef heart enzyme the ND-1 product was detected to be among the polypeptides reacting with the inhibitor. 5. Competition experiments employing either NADH or decylbenzoquinone (DB), together with the pethidine analogue, showed that both enzyme substrates interfere specifically with the inhibitor binding to complex I.

Synthesis and biological activity of fluoroalkylamine derivatives of narcotic analgesics.

N-Ethyl-, N-(2-fluoroethyl)-, N-(2,2-difluoroethyl)-, and N-(2,2,2-trifluoroethyl)-substituted normeperidine (1b-e) and normetazocine (2b-e) derivatives were prepared. The analgesic activities of the compounds were determined in mice. Opiate receptor binding studies, in the presence and absence of sodium ion, were carried out. The antagonist activities of normetazocine derivatives were studied in monkeys. These were further examined in the isolated guinea pig ileum for relative agonist activity. The pKa values were measured; in vivo agonist acitivty was lost with weakly basic derivatives. For the normetazocine derivatives, opiate receptor binding data were consistent with guinea pig ileum agonist potency and mouse vas deferens antagonist potency but not with in vivo data. Opiate receptor binding was reduced for the less basic normetazocine derivatives. In the normeperidine series, there was no apparent direct relationship between pKa and opiate receptor binding. However, a relationship involving the hydrophobic character of the N-substituent is discussed. The N-(2-fluoroethyl) derivatives in both series were found to cause convulsions in rats at doses of 40-45 mg/kg ip. Elevated serum citrate levels were found in these rats, implicating in vivo oxidative deamination of the N-(fluoroalkyl) substituent to fluoroacetate.

Some spiro analogues of the potent analgesic ketobemidone.

A series of spiro analogues of the potent narcotic ketobemidone have been prepared and found to be devoid of opiate activity. Additional pharmacology and possible implications for the mode of binding of ketobemidone to the analgesic receptor are discussed.

N-(2-Cyanoethyl) derivatives of meperidine, ketobemidone, and a potent 6,7-benzomorphan.

The N-(2-cyanoethyl)-9alpha-ethyl-5-methyl-6,7-benzomorphan (1c) is a more potent antinociceptive and has stronger receptor binding affinity than its N-methyl analogue 1b. The N-(2-cyanoethyl)-4-phenylpiperidine compounds 2b and 3b were almost inactive compared to their N-methyl congeners 2a and 3a, respectively. It appears that the pharmacological effect of the N-(2-cyanoethyl) moiety is dependent on the opioid on which it is substituted.

Stereochemical studies on medicinal agents. 20. Absolute configuration and analgetic potency alpha-promedol enantiomers. The role of the C-4 chiral center in conferring stereoselectivity in axial- and equatorial-phenyl prodine congeners.

Opical antipodes of the axial phenyl analgetic, alpha-promedol hydrochloride (3), were prepared and the absolute stereochemistry wasd determined by relating one of the enantiomers to its gamme diastereomer having the 2S, 4S,5R configuration. The analegetic potency of (+)-(2R,4S,5S)-3 is 20 times that of morphine, while its enantiomer, (-)-(2S,4R,5R)-3, is inactive at 50 mg/kg. These results are in accord with prior reports which indicate that substitution of a 3-or 5-alkyl group on the pro-4S enantiotopic edge of the piperidine ring leads to enantiomers which have greater potency than those substituted in an identical position on the pro-4R edge. This coupled with the fact that the torsion angle between the axial phenyl group and piperidine ring in (+)-3 is of the same sign as its equatorial congeners, suggests that the C(3)-C(4)-C(5) moiety and its substituents at C(4) are located in a similar chiral environment on the receptor. In contrast, the C(2)-N-C(6) portion of the axial and equatorial molecules does not bind in the same receptor environment, and it is suggested that different modes of interaction in the prodine series arise from different orientations of this moiety.

Relationship between analgetic ED50 dose and time-course brain levels N-alkylnormeperidine homologues.

The brain levels of meperidine and three N-alkyl homologues were determined at equal analgetic iv doses in mice. The relative levels of the four compounds in brain were found to be closely proportional to their ED50 doses even though the compounds exhibit a wide range in partition coefficient and metabolic N-dealkylation. While lipid solubility and metabolism are undoubtedly important factors in the overall time-course brain levels, it appears that during the period of analgetic measurement (5-60 min after injection) these factors do not profoundly affect the relative brain levels because peak uptake occurs within the first 5 min after administration of the homologues. As a consequence, the observed ED50 potencies appear to provide a fair approximation of the relative receptor affinities of the four homologues. N-Dealkylation was observed as a major metabolic transformation by mouse liver in vivo for all four compounds, and the extent of this N-dealkylation was found to directly correspond to the rates of N-dealkylation by mouse liver homogenate seen in an earlier study.

Analgesic activity of the epimeric tropane analogs of meperidine. A physical and pharmacological study.

Condensation of cis-N-benzyl-2,5-bis(chloromethyl)pyrrolidine (6) and phenylacetonitrile afforded a mixture of epimers 7 and 8. Compound 8 was readily converted to the meperidine analog 1 prepared earlier by Bell and Archer. Compound 7 was converted to a new tropane analog of meperidine, compound 3. The ED50 of 1 and 3 in the D'Amour-Smith "tail flick" test for narcotic type analgesia, which differs by a factor of only 3 or 4 potency, supports the accumulated data that suggest that the analgesic activity of the meperidine type is not very sensitive to the conformation of the phenyl group in 4-phenylpiperidines. A proton and 13C magnetic resonance spectral comparison of 1 and 3, as well as a reevaluation of the conformational requirements of 17-19, leads to the conclusion that the differences in conformation of 1,3,17, and 18 are due to the varying degrees of flattening of piperidine ring. The 1H NMR and 13C NMR data are not consistent with the boat conformation suggested earlier for compound 17.