8-Carboxamidocyclazocine analogues: redefining the structure-activity relationships of 2,6-methano-3-benzazocines

A systematic review on the kappa opioid receptor and its ligands: New directions for the treatment of pain, anxiety, depression, and drug abuse

Kappa opioid receptor (KOR) is a member of the opioid receptor system, the G protein-coupled receptors that are expressed throughout the peripheral and central nervous systems and play crucial roles in the modulation of antinociception and a variety of behavioral states like anxiety, depression, and drug abuse. KOR agonists are known to produce potent analgesic effects and have been used clinically for the treatment of pain, while KOR antagonists have shown efficacy in the treatment of anxiety and depression. This review summarizes the history, design strategy, discovery, and development of KOR ligands. KOR agonists are classified as non-biased, G protein-biased, and β-arrestin recruitment-biased, according to their degrees of bias. The mechanisms and associated effects of the G protein signaling pathway and β-arrestin recruitment signaling pathway are also discussed. Meanwhile, KOR antagonists are classified as long-acting and short-acting, based on their half-lives. In addition, we have special sections for mixed KOR agonists and selective peripheral KOR agonists. The mechanisms of action and pharmacokinetic, pharmacodynamic, and behavioral studies for each of these categories are also discussed in this review.

Benzomorphan skeleton, a versatile scaffold for different targets: A comprehensive review

Despite the fact that the benzomorphan skeleton has mainly been employed in medicinal chemistry for the development of opioid analgesics, it is a versatile structure. Its stereochemistry, as well as opportune modifications at the phenolic hydroxyl group and at the basic nitrogen, play a pivotal role addressing the benzomorphan-based compounds to a specific target. In this review, we describe the structure activity-relationships (SARs) of benzomorphan-based compounds acting at sigma 1 receptor (σ1R), sigma 2 receptor (σ2R), voltage-dependent sodium channel, N-Methyl-d-Aspartate (NMDA) receptor-channel complex and other targets. Collectively, the SARs data have highlighted that the benzomorphan nucleus could be regarded as a useful template for the synthesis of drug candidates for different targets.

Benzomorphan scaffold for opioid analgesics and pharmacological tools development: A comprehensive review

Benzomorphan, derived by morphine skeleton simplification, has been the subject of exploration in medicinal chemistry for the development of new drugs and pharmacological tools to explore opioid pharmacology in vitro and in vivo. Building upon these evidences, the design and synthesis of benzomorphan-based compounds, appropriately modified at the basic nitrogen and/or the phenolic hydroxyl (8-OH) group, represent a valid and versatile strategy to obtain analgesics. In this review, to improve the body of information in this field, we report structure activity-relationships (SARs) of benzomorphan-based compounds analysing data literature of last 25 years. Collectively, SARs data highlighted that the benzomorphan nucleus represents a template in the achievement of a specific functional profile, by modifying N-substituent or 8-OH group.

Mixed κ/μ partial opioid agonists as potential treatments for cocaine dependence

Cocaine use activates the dopamine reward pathway, leading to the reinforcing effects of dopamine. There is no FDA-approved medication for treating cocaine dependence. Opioid agonists and antagonists have been approved for treating opioid and alcohol dependence. Agonists that activate the μ opioid receptor increase dopamine levels in the nucleus accumbens, while μ receptor antagonists decrease dopamine levels by blocking the effects of endogenous opioid peptides. Activation of the κ opioid receptor decreases dopamine levels and leads to dysphoria. In contrast, inhibition of the κ opioid receptor decreases dopamine levels in the nucleus accumbens. Antagonists acting at the κ receptor reduce stress-mediated behaviors and anxiety. Mixed partial μ/κ agonists have the potential of striking a balance between dopamine levels and attenuating relapse to cocaine. The pharmacological properties of mixed μ/κ opioid receptor agonists will be discussed and results from clinical and preclinical studies will be presented. Results from studies with some of the classical benzomorphans and morphinans will be presented as they lay the foundation for structure-activity relationships. Recent results with other partial opioid agonists, including buprenorphine derivatives and the mixed μ/κ peptide CJ-15,208, will be discussed. The behavioral effects of the mixed μ/κ MCL-741, an aminothiazolomorphinan, in attenuating cocaine-induced locomotor activity will be presented. While not a mixed μ/κ opioid, results obtained with GSK1521498, a μ receptor inverse agonist, will be discussed. Preclinical strategies and successes will lay the groundwork for the further development of mixed μ/κ opioid receptor agonists to treat cocaine dependence.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 9: Synthesis, characterization and molecular modeling of pyridinyl isosteres of N-BPE-8-CAC (1), a high affinity ligand for opioid receptors

Derivatives of the lead compound N-BPE-8-CAC (1) where each CH of the biphenyl group was individually replaced by N were prepared in hopes of identifying high affinity ligands with improved aqueous solubility. Compared to 1, binding affinities of the five possible pyridinyl derivatives for the μ opioid receptor were between threefold lower to fivefold higher with the Ki of the most potent compound being 0.064 nM. Docking of 8-CAC (2) into the unliganded binding site of the mouse μ opioid receptor (pdb: 4DKL) revealed that 8-CAC and β-FNA (from 4DKL) make nearly identical interactions with the receptor. However, for 1 and the new pyridinyl derivatives 4-8, binding is not tolerated in the 8-CAC binding mode due to the steric constraints of the large N-substituents. Either an alternative binding mode or rearrangement of the protein to accommodate these modifications may account for their high binding affinity.

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).

Semisynthetic neoclerodanes as kappa opioid receptor probes

Modification of the furan ring of salvinorin A (1), the main active component of Salvia divinorum, has resulted in novel neoclerodane diterpenes with opioid receptor affinity and activity. Conversion of the furan ring to an aldehyde at the C-12 position (5) has allowed for the synthesis of analogues with new carbon-carbon bonds at that position. Previous methods for forming these bonds, such as Grignard and Stille conditions, have met with limited success. We report a palladium catalyzed Liebeskind-Srogl cross-coupling reaction of a thioester and a boronic acid that occurs at neutral pH and ambient temperature to produce ketone analogs at C-12. To the best of our knowledge, this is the first reported usage of the Liebeskind-Srogl reaction to diversify a natural product scaffold. We also describe a one-step protocol for the conversion of 1 to 12-epi-1 (3) through microwave irradiation. Previously, this synthetically challenging process has required multiple steps. Additionally, we report in this study that alkene 9 and aromatic analogues 12, 19, 23, 25, and 26 were discovered to retain affinity and selectivity at kappa opioid receptors (KOP). Finally, we report that the furan-2-yl analog of 1 (31) has similar affinity to 1. Collectively, these findings suggest that different aromatic groups appended directly to the decalin core may be well tolerated by KOP receptors, and may generate further ligands with affinity and activity at KOP receptors.

Twin and triplet drugs in opioid research

Twin and triplet drugs are defined as compounds that contain respectively two and three pharmacophore components exerting pharmacological effects in a molecule. The twin drug bearing the same pharmacophores is a "symmetrical twin drug", whereas that possessing different pharmacophores is a "nonsymmetrical twin drug." In general, the symmetrical twin drug is expected to produce more potent and/or selective pharmacological effects, whereas the nonsymmetrical twin drug is anticipated to show both pharmacological activities stemming from the individual pharmacophores (dual action). On the other hand, nonsymmetrical triplet drugs, which have two of the same pharmacophores and one different moiety, are expected to elicit both increased pharmacological action and dual action. The two identical portions could bind the same receptor sites simultaneously while the third portion could bind a different receptor site or enzyme. This review will mainly focus on the twin and triplet drugs with an evaluation of their in vivo pharmacological effects, and will also include a description of their pharmacology and synthesis.

Agonist vs antagonist behavior of delta opioid peptides containing novel phenylalanine analogues in place of Tyr(1)

The novel phenylalanine analogues 4'-[N-((4'-phenyl)phenethyl)carboxamido]phenylalanine (Bcp) and 2',6'-dimethyl-4'-[N-((4'-phenyl)phenethyl)carboxamido]phenylalanine (Dbcp) were substituted for Tyr(1) in the delta opioid antagonist TIPP (H-Tyr-Tic-Phe-Phe-OH; Tic = tetrahydroisoquinoline-3-carboxylic acid). Unexpectedly, [Bcp(1)]TIPP was a potent, selective delta opioid agonist, whereas [Dbcp(1)]TIPP retained high delta antagonist activity. Receptor docking studies indicated similar binding modes for the two peptides except for the biphenylethyl moiety which occupied distinct receptor subsites. The dipeptide H-Dbcp-Tic-OH was a highly selective delta antagonist with subnanomolar delta receptor affinity.

Palladium-catalyzed carbonylation reactions of aryl halides and related compounds

Palladium-catalyzed carbonylation reactions of aromatic halides in the presence of various nucleophiles have undergone rapid development since the pioneering work of Heck and co-workers in 1974, such that nowadays a plethora of palladium catalysts are available for different carbonylative transformations. The carboxylic acid derivatives, aldehydes, and ketones prepared in this way are important intermediates in the manufacture of dyes, pharmaceuticals, agrochemicals, and other industrial products. In this Review, the recent academic developments in this area and the first industrial processes are summarized.

Syntheses of novel high affinity ligands for opioid receptors

A series of novel high affinity opioid receptor ligands have been made whereby the phenolic-OH group of nalbuphine, naltrexone methiodide, 6-desoxonaltrexone, hydromorphone and naltrindole was replaced by a carboxamido group and the furan ring was opened to the corresponding 4-OH derivatives. These furan ring 'open' derivatives display very high affinity for mu and kappa receptors and much less affinity for delta. The observation that these target compounds have much higher receptor affinity than the corresponding ring 'closed' carboxamides significantly strengthens our underlying pharmacophore hypothesis concerning the bioactive conformation of the carboxamide group.

Cyclic enkephalin analogs containing various para-substituted phenylalanine derivatives in place of Tyr1 are potent opioid agonists*

The cyclic enkephalin analog H-Tyr-c[D-Cys-Gly-Phe(pNO(2))-D-Cys]NH(2) is a highly potent opioid agonist with IC(50)s of 35 pm and 19 pm in the guinea-pig ileum (GPI) and mouse vas deferens (MVD) assays, respectively. The Phe(1)-analog of this peptide showed 370-fold and 6790-fold lower agonist potency in the GPI and MVD assays, respectively, indicating the importance of the Tyr(1) hydroxyl-group in the interaction with mu and delta opioid receptors. In the present study, the effect of various substituents (-NH(2), -NO(2), -CN, -CH(3), -COOH, -COCH(3), -CONH(2)) introduced in the para-position of the Phe(1)-residue of H-Phe-c[D-Cys-Gly-Phe(pNO(2))-D-Cys]NH(2) on the in vitro opioid activity profile was examined. Most analogs showed enhanced mu and delta agonist potencies in the two bioassays, except for the Phe(pCOOH)(1)-analog, which was weakly active, probably as a consequence of the negative charge. The most potent compounds were the Phe(pCOH(3))(1)- and the Phe(pCONH(2))(1)-analogs. The latter compound showed subnanomolar mu and delta agonist potencies and represents the most potent enkephalin analog lacking the Tyr(1) hydroxyl-group reported to date. Taken together, these results indicate that various substituents introduced in the para-position of Phe(1) enhance opioid activity via hydrogen bonding or hydrophobic interactions with the receptor. Comparison with existing structure-activity relationship on phenolic hydroxyl replacements in morphinans indicates that these nonpeptide opiates and some of the cyclic enkephalin analogs described here may have different modes of binding to the receptor.

Syntheses and opioid receptor binding properties of carboxamido-substituted opioids

A series of 15 novel opioid derivatives were made where the prototypic phenolic-OH group of traditional opioids was replaced by a carboxamido (CONH(2)) group. For 2,6-methano-3-benzazocines and morphinans similar or, in a few instances, enhanced affinity for mu, delta and kappa opioid receptors was observed when the OH-->CONH(2) switch was applied. For 4,5alpha-epoxymorphinans, binding affinities for the corresponding carboxamide derivatives were much lower than the OH partner consistent with our pharmacophore hypothesis concerning carboxamide bioactive conformation. The active metabolite of tramadol and its carboxamide counterpart had comparable affinities for the three 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.

Synthesis and in vitro opioid receptor functional antagonism of analogues of the selective kappa opioid receptor antagonist (3R)-7-hydroxy-N-((1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic)

In previous structure-activity relationship (SAR) studies, we identified (3 R)-7-hydroxy- N-((1 S)-1-{[(3 R,4 R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl}-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic, 1) as the first potent and selective kappa opioid receptor antagonist from the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of opioid antagonist. In the present study, we report the synthesis and in vitro opioid receptor functional antagonism of a number of analogues of 1 using a [ (35) S]GTPgammaS binding assay. The results from the studies better define the pharmacophore for this class of kappa opioid receptor antagonist and has identified new potent and selective kappa antagonist. (3 R)-7-Hydroxy- N-[(1 S,2 S)-1-{[(3 R,4 R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidin-1-yl]methyl}-2-methylbutyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide ( 3) with a K e value of 0.03 nM at the kappa receptor and 100- and 793-fold selectivity relative to the mu and delta receptors was the most potent and selective kappa opioid receptor antagonist identified.

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.

Structure-activity relationships of Leu-enkephalin analog with (4-carboxamido)phenylalanine substituted for tyrosine: A molecular dynamics study

Motivated by recent experimental work on Leu-Enkephalin modification with (4-Carboxamido)phenylalanine (Cpa), we perform MD simulations to study the structure-activity relationships of the [Cpa(1), Leu(5)]-enkephalin (Cpa-LE) for better understandings of the binding affinity in delta-selective opioid ligands. Recently, Tyr(1) substituted into Cpa(1) form was experimentally found to be the first example of an amino acid that acts as a surrogate for Tyr(1) in opioid peptide ligands, which challenges a long-standing belief that a phenolic residue is required for high affinity binding. Our simulations show the Cpa-LE structure in aqueous solution revealed that the occurrence of single-bend packed state can be stabilized by an intramolecular hydrogen bond from Leu(5)-NH to Gly(2)-CO (5-->2). In addition, an intramolecular sidechain to backbone hydrogen bond, i.e., hydrogen bond binding between the sidechain carbonyl CO group of the Cpa residue and backbone amide NH group of the Phe residue was examined. Furthermore, the hydration effects of carboxamido group (CONH(2)) for Cpa residue and 5-->2 hydrogen bond were calculated via the solute-solvent radial distribution functions g(alpha-beta) (r), providing direct evidence of strong hydrogen bond interactions. Our simulation results further reveal the chi(1) rotamers of the Cpa(1) and Phe(4) that show preferences for trans and gauche (-), respectively. Finally, we elucidate the probability distributions of two aromatic rings among the Cpa-LE, Leu-enkephalin, and delta pharmacophore model. The results show that modified the Tyr(1) to Cpa(1) can lead to increase the potency and selectivity for delta-opioid receptor (DOR), consistent with experimental findings.

Identification of potent phenyl imidazoles as opioid receptor agonists

Using previously reported opioid receptor (OR) agonist analogs 4a-c as starting points, the structure-activity relationship (SAR) for their related series has been further refined. This SAR study has led to the identification of 2,6-di-Me-Tyr (DMT) analogs 4h and 4j as the most potent OR agonist within the series. In addition, it was discovered that 4-(aminocarbonyl)-2,6-dimethyl-Phe is a reasonable bioisostere surrogate for the DMT moiety, as supported by the OR activities of compounds 4x and 4y.

Kappa opioids as potential treatments for stimulant dependence

Stimulant abuse is a major problem in the United States and the development of pharmacological treatments for stimulant abuse remains an important therapeutic goal. Classically, the "dopamine hypothesis" has been used to explain the development of addiction and dependence of stimulants. This hypothesis involves the direct increase of dopamine as the major factor in mediating the abuse effects. Therefore, most treatments have focused on directly influencing the dopamine system. Another approach, which has been explored for potential treatments of stimulant abuse, is the use of kappa opioid agonists. The kappa receptor is known to be involved, via indirect effects, in synaptic dopamine levels. This review covers several classes of kappa opioid ligands that have been explored for this purpose.

SAR and biological evaluation of novel trans-3,4-dimethyl-4-arylpiperidine derivatives as opioid antagonists

The phenolic hydroxy group of opiate-derived ligands is of known importance for biological activity. We have developed a SAR study around LY255582 by comparing the effect of the hydroxy group in the 2- and 4-position of the phenyl ring. Also, we have proved that the 3-position of the phenyl ring is optimal for opioid activity. Furthermore, we have successfully replaced the hydroxy group in LY255582 by carbamate and carboxamide groups. The new analogs have high affinity for the opioid receptors comparable to the corresponding phenol. Carboxamide analog 12 has an improved metabolism profile and proved to be efficacious in in vivo studies.

Redefining the structure-activity relationships of 2,6-methano-3-benzazocines. Part 3: 8-Thiocarboxamido and 8-thioformamido derivatives of cyclazocine

8-Position variants of cyclazocine have been made where the phenolic 8-OH was replaced by thioamide, amidine, guanidine, urea and thiourea groups. High affinity for opioid receptors was observed for the 8-CSNH2 and 8-NHCHS analogues indicating that these groups are isosteric with not only the 8-OH but with the previously synthesized 8-CONH2 and 8-NHCHO cyclazocine derivatives.

Synthesis and opioid receptor binding properties of a highly potent 4-hydroxy analogue of naltrexone

Very high affinity for opioid receptors (e.g., K(i)=0.052nM for mu) has been observed in the rationally designed naltrexone analogue 5. SAR and physical data supports the hypothesis that the 4-OH group of 5 stabilizes the 3-carboxamido group in the putative bioactive conformation.

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.

(4-Carboxamido)phenylalanine is a surrogate for tyrosine in opioid receptor peptide ligands

(S)-4-(Carboxamido)phenylalanine (Cpa) is examined as a bioisosteric replacement for the terminal tyrosine (Tyr) residue in a variety of known peptide ligands for the mu, delta and kappa opioid receptors. The Cpa-containing peptides, assayed against cloned human opioid receptors, display comparable binding affinity (Ki), and agonist potency (EC50) to the parent ligands at the three receptors. Cpa analogs of delta selective peptides show an increase in delta selectivity relative to the mu receptor. Cpa is the first example of an amino acid that acts as a surrogate for Tyr in opioid peptide ligands, challenging the long-standing belief that a phenolic residue is required for high affinity binding.

10-Ketomorphinan and 3-substituted-3-desoxymorphinan analogues as mixed kappa and micro opioid ligands: synthesis and biological evaluation of their binding affinity at opioid receptors

A series of 10-ketomorphinan analogues were synthesized, and their binding affinity at all three opioid receptors was investigated. In most cases, high affinity at micro and kappa receptors, and lower affinity at delta receptor was observed, resulting in good selectivity for micro and kappa receptors. A wide range of substituents can be accommodated on the nitrogen position. The N-(S)-tetrahydrofurfuryl analogue 11 displayed the highest affinity at all three receptors. The N-cyclobutylmethyl analogue 13 gave both high affinity and selectivity at kappa receptor, and N-2-phenylethyl analogue 18 exhibited good affinity and selectivity at micro receptor. Further modifications of the 3-substituent indicated that one H-bond donor was an essential requirement for good affinity at micro and kappa receptors. Similar modifications were investigated at the 3-OH group of morphinans: levorphanol (2a), cyclorphan (2b), and MCL-101 (2c) lacking the 10-keto group. The 3-amino bioisosteric analogues (40 and 41) displayed reasonably good affinity at micro and kappa receptors. The 3-carboxamido replacement (compounds 46-48) in the morphinan subseries resulted in similar affinities comparable to their corresponding 3-OH congeners. The high affinity of these carboxamido analogues, along with their greater lipophilicity and metabolic stability, make them promising candidates for further pharmacological investigation.

κ-Opioid Receptor Ligands Inhibit Cocaine-Induced HIV-1 Expression in Microglial Cells

Cocaine abuse has been implicated as a cofactor in human immunodeficiency virus (HIV)-1-associated dementia (HAD). In this study, we tested the hypothesis that exposure of microglial cells, the resident macrophages of the brain, to cocaine would potentiate HIV-1 expression. Because kappa-opioid receptor (KOR) agonists have been shown to suppress neurochemical and neurobehavioral responses to cocaine and to inhibit HIV-1 expression in microglial cell cultures, we also postulated that KOR ligands would inhibit cocaine-induced potentiation of HIV-1 expression. Human microglial cells were infected with HIV-1(SF162), an R5 isolate, and viral expression was quantified by measurement of p24 antigen in culture supernatants. Treatment of microglia with the KOR agonists trans-(+/-)-3,4-dichlor-N-methyl-N-(2[1-pyrrolidnyl])benzeneacetamide methanesulfonate and 8-carboxamidocyclazocine inhibited viral expression (maximal suppression of 42 and 48%, respectively). Consistent with the hypotheses, treatment of microglia with cocaine promoted HIV-1 expression (maximal enhancement of 54%), and pretreatment of microglia with these KOR agonists as well as with the KOR-selective antagonist nor-binaltorphimine abrogated cocaine-induced potentiation of viral expression. Results of flow cytometry studies suggested that the mechanism whereby KOR ligands inhibit cocaine's stimulatory effect on viral expression involves the suppression of cocaine-induced activation of extracellular signal-regulated kinase1/2, thereby blunting cocaine-enhanced up-regulation of the HIV-1 entry chemokine coreceptor CCR5. The findings of this study suggest that in addition to its neurotoxic effects, cocaine could foster development of HAD by potentiating viral expression in the brain and that this phenomenon is inhibited by KOR ligands.

trans -3,4-Dimethyl-4-(3-carboxamidophenyl)piperidines: A novel class of μ-Selective opioid antagonists

trans-3,4-Dimethyl-4-(3-carboxamidophenyl)piperidines constitute a novel class of micro opioid receptor antagonists. The CONH(2) group was found to be an effective isostere of the phenolic OH moiety. Structure-activity relationships at the piperidine nitrogen position led to the identification of several ligands displaying high affinity toward the cloned human micro opioid receptors, good selectivity micro/delta, micro/kappa, and potent in vitro antagonist activity.

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 </=1 nM observed for the (2R,6R,11R)-isomer, (-)-4. A preliminary SAR revealed that affinity is very sensitive to substitution on the formamide appendage.

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.

3-Carboxamido analogues of morphine and naltrexone. synthesis and opioid receptor binding properties

In response to the unexpectedly high affinity for opioid receptors observed in a novel series of cyclazocine analogues where the prototypic 8-OH was replaced by a carboxamido group, we have prepared the corresponding 3-CONH(2) analogues of morphine and naltrexone. High affinity (K(i)=34 and 1.7nM) for mu opioid receptors was seen, however, the new targets were 39- and 11-fold less potent than morphine and naltrexone, respectively.