Novel N-normetazocine Derivatives with Opioid Agonist/Sigma-1 Receptor Antagonist Profile as Potential Analgesics in Inflammatory Pain.

Although opioids and nonsteroidal anti-inflammatory drugs (NSAIDs) are the most common drugs used in persistent pain treatment; they have shown many side effects. The development of new analgesics endowed with mu opioid receptor/delta opioid receptor (MOR/DOR) activity represents a promising alternative to MOR-selective compounds. Moreover, new mechanisms, such as sigma-1 receptor (σ1R) antagonism, could be an opioid adjuvant strategy. The in vitro σ1R and σ2R profiles of previous synthesized MOR/DOR agonists (-)-2R/S-LP2 (1), (-)-2R-LP2 (2), and (-)-2S-LP2 (3) were assayed. To investigate the pivotal role of N-normetazocine stereochemistry, we also synthesized the (+)-2R/S-LP2 (7), (+)-2R-LP2 (8), and (+)-2S-LP2 (9) compounds. (-)-2R/S-LP2 (1), (-)-2R-LP2 (2), and (-)-2S-LP2 (3) compounds have Ki values for σ1R ranging between 112.72 and 182.81 nM, showing a multitarget opioid/σ1R profile. Instead, (+)-2R/S-LP2 (7), (+)-2R-LP2 (8), and (+)-2S-LP2 (9) isomers displayed a nanomolar affinity for σ1R, with significative selectivity vs. σ2R and opioid receptors. All isomers were evaluated using an in vivo formalin test. (-)-2S-LP2, at 0.7 mg/kg i.p., showed a significative and naloxone-reversed analgesic effect. The σ1R selective compound (+)-2R/S-LP2 (7), at 5.0 mg/kg i.p., decreased the second phase of the formalin test, showing an antagonist σ1R profile. The multitarget or single target profile of assayed N-normetazocine derivatives could represent a promising pharmacological strategy to enhance opioid potency and/or increase the safety margin.

Acid-mediated ring-expansion reaction of N-aryl-2-vinylazetidines: synthesis and unanticipated reactivity of tetrahydrobenzazocines.

The aza-Clasen rearrangement of N-aryl-2-vinylazetidines has been explored. N-Aryl-2-vinylazetidines were transformed to corresponding tetrahydrobenzazocines in good yields. Unexpectedly, the tetrahydrobenzazocine was unstable and readily isomerized to vinyltetrahydroquinoline in the presence of acid. The mechanism of this ring contraction was studied in detail.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 8. High affinity ligands for opioid receptors in the picomolar Ki range: oxygenated N-(2-[1,1'-biphenyl]-4-ylethyl) analogues of 8-CAC.

N-[2-(4'-methoxy[1,1'-biphenyl]-4-yl)ethyl]-8-CAC (1) is a high affinity (K(i)=0.084 nM) ligand for the µ opioid receptor and served as the lead compound for this study. Analogues of 1 were made in hopes of identifying an SAR within a series of oxygenated (distal) phenyl derivatives. A number of new analogues were made having single-digit pM affinity for the µ receptor. The most potent was the 3',4'-methylenedioxy analogue 18 (K(i)=1.6 pM).

Asymmetric syntheses of (-)-pentazocine and (-)-eptazocine through an aza-Prins cyclization.

Two down more to go: The asymmetric syntheses of (-)-pentazocine and (-)-eptazocine are presented. The highlights of the syntheses are the construction of the core skeleton through an aza-Prins cyclization and intramolecular Friedel-Crafts reaction.

Structures in solutions from joint experimental-computational analysis: applications to cyclic molecules and studies of noncovalent interactions.

The potential of an approach combining nuclear magnetic resonance (NMR) spectroscopy, molecular dynamics (MD) simulations, and quantum mechanical (QM) calculations for full structural characterizations in solution is assessed using cyclic organic compounds, namely, benzazocinone derivatives 1-3 with fused five- and eight-membered aliphatic rings, camphoric anhydride 4, and bullvalene 5. Various MD simulations were considered, using force field and semiempirical QM treatments, implicit and explicit solvation, and high-temperature MD calculations for selecting plausible molecular geometries for subsequent QM geometry optimizations using mainly B3LYP, M062X, and MP2 methods. The QM-predicted values of NMR parameters were compared to their experimental values for verification of the final structures derived from the MD/QM analysis. From these comparisons, initial estimates of quality thresholds (calculated as rms deviations) were 0.7-0.9 Hz for (3)J(HH) couplings, 0.07-0.11 Å for interproton distances, 0.05-0.08 ppm for (1)H chemical shifts, and 1.0-2.1 ppm for (13)C chemical shifts. The obtained results suggest that the accuracy of the MD analysis in predicting geometries and relative conformational energies is not critical and that the final geometry refinements of the structures selected from the MD simulations using QM methods are sufficient for correcting for the expected inaccuracy of the MD analysis. A unique example of C(sp(3))-H···N(sp(3)) intramolecular noncovalent interaction is also identified using the NMR/MD/QM and the natural bond orbital analyses. As the NMR/MD/QM approach relies on the final QM geometry optimization, comparisons of geometric characteristics predicted by different QM methods and those from X-ray and neutron diffraction measurements were undertaken using rigid and flexible cyclic systems. The joint analysis shows that intermolecular noncovalent interactions present in the solid state alter molecular geometries significantly compared to the geometries of isolated molecules from QM calculations.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 7: syntheses and opioid receptor properties of cyclic variants of cyclazocine.

A series of 7,8- and 8,9-fused triazole and imidazole analogues of cyclazocine have been made and characterized in opioid receptor binding and [(35)S]GTPgammaS assays. Target compounds were designed to explore the SAR surrounding our lead molecule for this study, namely the 8,9-fused pyrrolo analogue 2 of cyclazocine. Compared to 2, many of the new compounds in this study displayed very high affinity for opioid receptors.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 6: Opioid receptor binding properties of cyclic variants of 8-carboxamidocyclazocine.

A series of 7,8- and 8,9-fused pyrimidinone, aminopyrimidine and pyridone derivatives of 8-carboxamidocyclazocine (8-CAC) have been prepared and evaluated in opioid receptor binding assays. Targets were designed to corroborate a pharmacophore hypothesis regarding the bioactive conformation of the carboxamide of 8-CAC. In addition to the results from this study strongly supporting this pharmacophore hypothesis, a number of novel compounds with high affinity to opioid receptors have been identified.

New benzomorphan derivatives of MPCB as MOP and KOP receptor ligands.

There is considerable interest in developing KOP Opioid receptor ligands as clinically useful analgesics. Moreover, compounds with mixed KOP receptor and mu-opioid peptide (MOP) receptor agonist/antagonist properties could have a better therapeutic potential. The benzomorphan-based synthetic ligands MPCB and CCB have been shown to bind KOP receptors with high affinity and selectivity. We report here a series of compounds synthesized to perform structure-affinity relationship (SAR) studies on MPCB. The aim of this study was to optimise KOP receptor-ligand interaction and to modulate MOP receptor selectivity. In the benzylamide analogue of MPCB (compound 9) the presence of a third aromatic nucleus, at an appropriate distance and conformation with respect to aromatic pharmacophoric residues, increased KOP receptor affinity by about 6-fold compared to MPCB (Ki = 35 nM and Ki = 240 nM, respectively). Instead, compound 28 with a tertiary amino group in the nitrogen substituent displayed a comparable KOP receptor affinity (Ki = 179 nM) but also high MOP receptor affinity (Ki = 45 nM). Thus, the present study shows that in benzomorphan-based ligands the presence of different functional groups in the nitrogen substituent, ranging from a positive charged amine to an additional aromatic ring, is able to promote the correct aligment of aromatic pharmacophoric residues with MOP and KOP receptor types. Evaluation of docking simulations of compounds 9 and 28 into the KOP and MOP receptor displayed selective ligand interactions with the important amino acid residues Tyr320 (TMVII) and Trp318 (TMVII), respectively.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. 5. Opioid receptor binding properties of N-((4'-phenyl)-phenethyl) analogues of 8-CAC.

A series of aryl-containing N-monosubstituted analogues of the lead compound 8-[N-((4'-phenyl)-phenethyl)]-carboxamidocyclazocine were synthesized and evaluated to probe a putative hydrophobic binding pocket of opioid receptors. Very high binding affinity to the mu opioid receptor was achieved though the N-(2-(4'-methoxybiphenyl-4-yl)ethyl) analogue of 8-CAC. High binding affinity to mu and very high binding affinity to kappa opioid receptors was observed for the N-(3-bromophenethyl) analogue of 8-CAC. High binding affinity to all three opioid receptors were observed for the N-(2-naphthylethyl) analogue of 8-CAC.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. 4. Opioid receptor binding properties of 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogues of cyclazocine and ethylketocycalzocine.

The synthesis and evaluation of a series of aryl-containing N-monosubstituted analogues of the lead compound 8-carboxamidocyclazocine were performed to probe a putative hydrophobic binding pocket of opioid receptors. High binding affinity to mu, kappa, and delta opioid receptors was observed for the 8-[N-(4'-phenyl)-phenethyl)carboxamido] analogue.

Effects of the mixed-action kappa/mu opioid agonist 8-carboxamidocyclazocine on cocaine- and food-maintained responding in rhesus monkeys.

The present study evaluated the effects of 8-carboxamidocyclazocine (8-CAC), a novel mixed-action kappa/mu agonist with a long duration of action, on food- and cocaine-maintained responding in rhesus monkeys to assess the potential utility of 8-CAC as a medication for the treatment of cocaine dependence. The effects of acute and chronic (10 days) 8-CAC were examined in rhesus monkeys responding under a multiple schedule for both cocaine and food reinforcement. Acute 8-CAC (0.032-0.56 mg/kg, i.m.) dose-dependently eliminated cocaine-maintained responding in all three monkeys. However, doses of 8-CAC that decreased cocaine self-administration typically also decreased food-maintained responding, and 8-CAC-induced decreases in cocaine self-administration diminished during chronic 8-CAC treatment. These results confirm that 8-CAC acutely decreases cocaine self-administration. However, non-selective effects of 8-CAC on food-maintained responding and tolerance to 8-CAC effects on cocaine self-administration may limit its potential for the treatment of cocaine dependence.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 2: 8-formamidocyclazocine analogues.

High affinity binding for mu and kappa opioid receptors has been observed in analogues of cyclazocine, ethylketocyclazocine and naltrexone where the prototypic (of opiates) phenolic OH group was replaced with a formamide (-NHCHO) group. For the 8-formamide analogue of cyclazocine, binding is highly enantiospecific (eudismic ratios approximately 2000 for mu and kappa) with K(i) values

8-Carboxamidocyclazocine: a long-acting, novel benzomorphan.

To obtain benzomorphans with a longer duration of action that may be potential therapeutics for treating cocaine abuse, 8-carboxamidocyclazocine was synthesized. The pharmacological properties of 8-carboxamidocyclazocine were compared with the parent compound cyclazocine. Changing the 8-hydroxyl group on cyclazocine to an 8-carboxamido group resulted in only a 2-fold decrease in the affinity of the compound for the kappa-receptor, and no change in the affinity for the mu-opioid receptor, with both compounds having K(i) values of less than 1 nM, based on radioligand binding assays. In the guanosine 5'-O -(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding assay, the two compounds produced moderate stimulation of GTP binding to the human kappa- and mu-receptors. When given by i.c.v. injection, the compounds produced less than 60% antinociception in the mouse 55 degrees C warm-water tail-flick test. However, in the mouse writhing test, the compounds had high potency in producing antinociception. Antinociception induced by either 8-carboxamidocyclazocine or cyclazocine was mediated by both kappa- and mu-opioid receptors. Cyclazocine acted as a mu-antagonist in addition to its agonist properties at the mu-receptor, as measured by the inhibition of morphine-induced antinociception. In contrast, 8-carboxamidocyclazocine did not inhibit morphine-induced antinociception, demonstrating that it was not a mu-opioid receptor antagonist in this assay. An i.p. injection of an ED(70) dose of 8-carboxamidocyclazocine produced antinociception that lasted for 15 h in contrast to cyclazocine, which produced antinociception, lasting 2 h. 8-Carboxamidocyclazocine is a novel, long-acting benzomorphan, which possesses pharmacological properties that are distinct from the properties of cyclazocine.

Synthesis of (+)-cis-N-(4-isothiocyanatobenzyl)-N-normetazocine, an isothiocyanate derivative of N-benzylnormetazocine as acylant agent for the sigma(1) receptor.

(+)-cis-N-(4-Isothiocyanatobenzyl)-N-normetazocine (BNIT) (+)-(4) was designed and synthesized as a derivative of the potent and selective sigma(1) receptor ligand (+)-cis-N-benzyl-N-normetazocine for irreversibly blocking sigma(1) binding sites. Pretreatment of guinea pig brain membranes with BNIT (0.1, 1, and 5 microM) caused a concentration-dependent loss of binding of the selective sigma(1) ligand [(3)H]-(+)-pentazocine. Binding experiments with [(3)H]-1,3-di(2-tolyl)guanidine ([(3)H]-DTG), a ligand of sigma(1) and sigma(2) receptors, showed that pretreatment with BNIT blocked only the sigma(1) component of [(3)H]-DTG binding.

Synthesis and pharmacological evaluation of potent and enantioselective sigma 1, and sigma 2 ligands.

In a previous study we found that substitutions of the (+)-cis-N-normetazocine nucleus of (+)-MPCB with 1-adamantanamine provide the compound (+/-)-10 with high affinity and selectivity for sigma receptors. Starting with this result we have synthesized a new series of eight 1-phenyl-2-cyclopropylmethylamines structurally related to (+/-)-10, and binding affinities, with respect to sigma 1, sigma 2, opioid and dopaminergic D2 receptors, have been reported. All compounds showed a negligible opioid and dopaminergic affinity and high selectivity for sigma receptors. Modifications on the amino moiety and methylcarboxyester group of 10 provide compounds with different sigma 1 and sigma 2 binding affinity and selectivity. Moreover, we have also synthesized the respective enantiomers of componds (+/-)-10 and (+/-)-18 in order to evaluate the enantioselectivity for sigma 1 and sigma 2 receptors. The binding data showed that carboxymethylester on the cyclopropane ring was more critical for enantioselectivity than the hydroxymethylenic group. In fact, the (-)-10 enantiomer showed a preference for sigma 1 whereas (+)-10 showed a preference for sigma 2.

Selective protection and functionalization of morphine: synthesis and opioid receptor binding properties of 3-amino-3-desoxymorphine derivatives.

As part of an effort to identify novel opioid receptor interactive agents, we recently prepared a series of 8-(substituted)amino analogues of cyclazocine. We found the chiral 8-phenylamino (NHC(6)H(5)) cyclazocine derivative to have subnanomolar affinity for kappa opioid receptors and a 2-fold lower affinity for mu, opioid receptors. To determine if the benefits of (substituted)amino groups could be extended to the morphine core structure, we have made five novel 3-amino-3-desoxymorphine derivatives of general structure 5 where RR'N = H(2)N, CH(3)NH, (CH(3))(2)N, C(6)H(5)NH, and C(6)H(5)CH(2)NH. Relative to morphine, these derivatives had 38-273-fold, 11-41-fold, and 10-141-fold lower affinity for mu, delta, and kappa opioid receptors, respectively. Target compounds were made via Pd-catalyzed amination of a morphine 3-trifluoromethylsulfonate substrate where the 6-OH group was protected with a tert-butyldiphenylsilyl group. To make 6-tert-butyldiphenylsilyloxymorphine selectively, a new high-yield method was developed whereby morphine was bis-silylated using normal conditions followed by selective removal of the 3-tert-butyldiphenylsilyl group with catalytic tetrabutylammonium fluoride.

Partial opioids. Medications for the treatment of pain and drug abuse.

Pentazocine and cyclazocine are two benzomorphans that were synthesized by the late Sydney Archer in 1962. These benzomorphans were synthesized as part of an effort to develop analgesics with little or no abuse potential. Pentazocine is used as an analgesic, often in individuals who have sever pain or in those who have drug-abuse problems. Cyclazocine is a low-liability analgesic and potential therapeutic for the treatment of drug abuse. The risk of drug dependence is lower with the benzomorphans, which usually act as partial agonists at the mu opioid receptor and as kappa agonists. In an attempt to synthesize analogs of cyclazocine with increased bioavailability and varying kappa agonist and partial mu agonist properties, a series of 8-amino derivatives of cyclazocine were synthesized. These compounds were characterized in radioligand binding assays for their affinity and selectivity for the mu, delta, and kappa opioid receptors. Mouse antinociceptive tests were used to characterize the agonist and antagonist properties of each compound at the mu, delta and kappa receptors.

Modeling of kappa-opioid receptor/agonists interactions using pharmacophore-based and docking simulations.

The interaction of the kappa-opioid receptor with arylacetamide and benzomorphan derivatives acting as agonists was modeled through pharmacophore-based and docking calculations. Potentially bioactive conformations of representative ligands (U-50,488 and its benzo-fused analogues 4 and 6 for arylacetamides and MPCB for benzomorphans) were identified by systematic conformational analysis and docked into a 3D model of the kappa-receptor. The obtained complexes, refined by energy-minimization and molecular dynamics, were evaluated for their consistency with structure-activity relationships and site-directed mutagenesis data. The following interactions are hypothesized to govern the ligand-receptor recognition process: (i) a salt bridge between the Asp138 carboxylate and the protonated nitrogen of the bound agonist; (ii) a hydrogen bond donated by the Tyr312 hydroxyl to the carbonyl oxygen of arylacetamides and MPCB; (iii) hydrophobic interactions established by the dichlorophenyl moiety of arylacetamides and the pendant phenyl ring of MPCB with the surrounding side chains of Tyr312, Leu224, Leu295, and Ala298; (iv) a pi-stacking contact between the Tyr312 side chain and the phenyl ring of arylacetamides; (v) a hydrogen bond linking the His291 imidazole ring to the phenolic hydroxy group featured by typical benzomorphans and the arylacetamides 4 and 6.

8-Aminocyclazocine analogues: synthesis and structure-activity relationships.

Opioid binding affinities were assessed for a series of cyclazocine analogues where the prototypic 8-OH substituent of cyclazocine was replaced by amino and substituted-amino groups. For mu and kappa opioid receptors, secondary amine derivatives having the (2R,6R,11R)-configuration had the highest affinity. Most targets were efficiently synthesized from the triflate of cyclazocine or its enantiomers using Pd-catalyzed amination procedures.

Pharmacokinetic/pharmacodynamic relationship of eptazocine, a narcotic-antagonist analgesic, in rats.

The relationship between the pharmacokinetics and the pharmacodynamics of eptazocine, a narcotic-antagonist analgesic, was investigated in rats. The analgesic effect of eptazocine (2.5, 5 and 10 mg/kg) following intravenous (i.v) administration was evaluated by both the Randall-Selitto method and the D'Amour-Smith method. The analgesic effects were determined before and at designed intervals for a period of 120 min after eptazocine administration, and are expressed as area under the effect-time curve (AUC(E)). The plasma concentration of eptazocine was determined by fluorescence HPLC and was analyzed with a two compartment open model using the nonlinear least-squares method. Eptazocine produced a dose-dependent analgesic effect. It was demonstrated that eptazocine has a linear relationship between AUC(E) and the area under the plasma concentration-time curve (AUC) following i.v. administration for three different doses ranging from 2.5 to 10 mg/kg.