Combination of cyclohexane and piperazine based κ-opioid receptor agonists: Synthesis and pharmacological evaluation of trans,trans-configured perhydroquinoxalines

Discovery of N'-benzyl-3-chloro-N-((1S,3R,4R)-3-((dimethylamino)methyl)-4-hydroxy-4-(3-methoxyphenyl)cyclohexyl)benzenesulfonamide as a novel selective KOR ligand

The effective management of moderate to severe pain often relies on the use of analgesic agents. However, the widespread utility of these medications is hindered by the occurrence of several undesirable side effects. In light of this challenge, there is growing interest in the development of κ opioid receptor (KOR) agonists, which have shown promise in mitigating these adverse effects. In this study, leveraging the structural scaffold of compound D (our previous study), we embarked on the design, synthesis, and evaluation of a series of N'-benzyl-3-chloro-N- ((1S,3R,4R)-3-((dimethylamino)methyl)-4-hydroxy-4-(3-methoxyphenyl)cyclohexyl)benzenesulfonamide derivatives. These compounds were subjected to comprehensive in vitro and in vivo test. Through systematic structure-activity relationship (SAR) exploration, we successfully identified compound 23p (Ki(KOR):1.9 nM) as a highly selective KOR ligand of new chemotype. 23p showed high clearance in vitro PK test, and abdominal contraction test showed potent antinociceptive effect. 23p and its O-demethyl metabolite 25 were both found in the plasma of mouse, 25 also showed potent affinity toward KOR (Ki(KOR): 3.1 nM), both they contribute to the analgesic effect. Moreover, 23p exhibited potent antinociceptive activity in abdominal constriction test, which was effectively abolished by pre-treatment of nor-BNI, a selective KOR antagonist.

Characterization of Pyrrolidinyl-hexahydro-pyranopiperazines as a Novel Kappa Opioid Receptor Agonist Scaffold

The kappa agonist structure-activity relationship around the novel, pyrrolidinyl substituted pyranopiperazine scaffold was developed. More specifically, the dichloroPhenylAcetamide-Pyrrolidinyl-PyranoPiperazine (PAPPP) core A was the focus of our work. The modulation of kappa receptor potency/G-protein activation and arrestin recruitment with respect to changes of the piperazine R group in A was demonstrated. Reduced β₂-arrestin recruitment and differential G-protein bias were observed for select analogues. To better understand the subtlety in receptor signaling, analogues were profiled as the resolved enantiomers. To determine in vivo target engagement, a subset of compounds was tested in mice for stimulation of serum prolactin, a neuroendocrine biomarker of KOR-agonist effects. Additional in vivo characterization included measurement of potential unwanted effects of kappa receptor activation such as sedation. These studies demonstrate a novel kappa receptor agonist scaffold with potential for G-protein signaling bias to probe in vivo pharmacology.

The effect of carbonyl on the isomerization of a galanthan ring system and total synthesis of (±)-β-lycorane

Lycorine-type alkaloids are privileged structures in drug development due to their attractive biological activities. In this paper, the carbonyl on the C ring was proved to have played a critical role in stereoselectivity during the synthesis process, and the galanthan skeleton with a cis-B/C ring is more thermodynamically stable in its presence. Furthermore, the total synthesis of (±)-β-lycorane was successfully completed by employing the Michael addition reaction to construct the galanthan skeleton with a trans-B/C ring. This system might be applied to other structural types with similar stereochemistry setting.

Signaling Properties of Structurally Diverse Kappa Opioid Receptor Ligands: Toward in Vitro Models of in Vivo Responses

Biased ligands preferentially activate certain signaling pathways downstream of their target receptor, leading to differential physiological or behavioral responses downstream. The kappa opioid receptor (KOR) is a drug target for diseases involving mood and reward, such as depression and addiction. Biased KOR ligands offer the potential to overcome negative side effects that have previously hampered the therapeutic development of KOR agonists by preferentially activating certain signaling pathways. Understanding relationships between ligand bias and behavior is difficult, however, because differences in cellular context and bias quantification methods lead to variation between studies. Here, a set of 21 structurally diverse KOR ligands were tested in parallel, to systematically quantify ligand bias at the KOR. Compounds included the endogenous peptide ligand Dynorphin A(1-17), two novel compounds synthesized for our research, and 18 additional compounds of different structural classes, including morphinans and the natural product Salvinorin A. Compounds were tested for their activity in early KOR signaling pathways (G-protein and β-arrestin recruitment) in KOR-expressing U2OS cells, and ligand bias was calculated. A subset of compounds was tested for sedative properties in the rotarod assay in mice. We found that rotarod sedation significantly correlated with β-arrestin signaling in this system, indicating that this in vitro system can be used to accurately describe this in vivo behavior caused by KOR agonists. Additionally, downstream signaling pathways ERK1/2 and mTOR were evaluated, and we determined that signaling via both of these pathways could diverge from KOR-mediated G-protein and arrestin signaling in this system.

Structurally Related Kappa Opioid Receptor Agonists with Substantial Differential Signaling Bias: Neuroendocrine and Behavioral Effects in C57BL6 Mice

BACKGROUND

The kappa opioid receptor system has been revealed as a potential pharmacotherapeutic target for the treatment of addictions to substances of abuse. Kappa opioid receptor agonists have been shown to block the rewarding and dopamine-releasing effects of psychostimulants. Recent investigations have profiled the in vivo effects of compounds biased towards G-protein-mediated signaling, with less potent arrestin-mediated signaling. The compounds studied here derive from a series of trialkylamines: N-substituted-N- phenylethyl-N-3-hydroxyphenylethyl-amine, with N-substituents including n-butyl (BPHA), methylcyclobutyl (MCBPHA), and methylcyclopentyl (MCPPHA).

METHODS

BPHA, MCBPHA, and MCPPHA were characterized in vitro in a kappa opioid receptor-expressing cell line in binding assays and functional assays. We also tested the compounds in C57BL6 mice, assaying incoordination with rotarod, as well as circulating levels of the neuroendocrine kappa opioid receptor biomarker, prolactin.

RESULTS

BPHA, MCBPHA, and MCPPHA showed full kappa opioid receptor agonism for G-protein coupling compared with the reference compound U69,593. BPHA showed no measurable β-arrestin-2 recruitment, indicating that it is extremely G-protein biased. MCBPHA and MCPPHA, however, showed submaximal efficacy for recruiting β-arrestin-2. Studies in C57BL6 mice reveal that all compounds stimulate release of prolactin, consistent with dependence on G-protein signaling. MCBPHA and MCPPHA result in rotarod incoordination, whereas BPHA does not, consistent with the reported requirement of intact kappa opioid receptor/β-arrestin-2 mediated coupling for kappa opioid receptor agonist-induced rotarod incoordination.

CONCLUSIONS

BPHA, MCBPHA, and MCPPHA are thus novel differentially G-protein-biased kappa opioid receptor agonists. They can be used to investigate how signaling pathways mediate kappa opioid receptor effects in vitro and in vivo and to explore the effects of candidate kappa opioid receptor-targeted pharmacotherapeutics.

Design and Synthesis of Enantiomerically Pure Decahydroquinoxalines as Potent and Selective κ-Opioid Receptor Agonists with Anti-Inflammatory Activity in Vivo

In order to develop novel κ agonists restricted to the periphery, a diastereo- and enantioselective synthesis of (4aR,5S,8aS)-configured decahydroquinoxalines 5-8 was developed. Physicochemical and pharmacological properties were fine-tuned by structural modifications in the arylacetamide and amine part of the pharmacophore as well as in the amine part outside the pharmacophore. The decahydroquinoxalines 5-8 show single-digit nanomolar to subnanomolar κ-opioid receptor affinity, full κ agonistic activity in the [³⁵S]GTPγS assay, and high selectivity over μ, δ, σ₁, and σ₂ receptors as well as the PCP binding site of the NMDA receptor. Several analogues were selective for the periphery. The anti-inflammatory activity of 5-8 after topical application was investigated in two mouse models of dermatitis. The methanesulfonamide 8a containing the (S)-configured hydroxypyrrolidine ring was identified as a potent (K_i = 0.63 nM) and highly selective κ agonist (EC₅₀ = 1.8 nM) selective for the periphery with dose-dependent anti-inflammatory activity in acute and chronic skin inflammation.

Synthesis and pharmacological evaluation of conformationally restricted κ-opioid receptor agonists

Additional N- and O-atoms in the bicyclic scaffold increase polarity and allow fine tuning of pharmacodynamic and pharmacokinetic properties of novel κ agonists.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Effects of polar κ receptor agonists designed for the periphery on ATP-induced Ca2+ release from keratinocytes

The very polar pyridylmethyl derivative 5a (log D_7.4 = 1.1) represents a potent and selective full κ-opioid receptor agonist (K_i = 0.13 nM, EC₅₀ = 33 nM), which reduced the release of Ca²⁺-ions into the cytoplasm in human keratinocytes.

Conformationally restricted κ-opioid receptor agonists: Synthesis and pharmacological evaluation of diastereoisomeric and enantiomeric decahydroquinoxalines

All diastereoisomeric decahydroquinoxalines representing conformationally restricted analogs of κ agonists U-50,488 and GR-89,696 have been prepared. Cis/trans configured compound 7 is by far the highest binding diastereoisomer with a Ki of 0.35 nM. Racemates 4, 6, and 7 were separated into enantiomers. (+)-(4aR,5S,8aS)-Configured enantiomer 7b was identified as a high affinity (Ki=0.25 nM) κ ligand with high selectivity over μ and δ receptors. It acts as full agonist with an EC50 value of 2.0 nM in the [(35)S]GTPγS assay, while enantiomer 7a showed an EC50 value of 1000 nM.

Diastereoselective Synthesis of Cyclic Five-Membered trans,trans-Configured Nitrodiols by Double Henry Reaction of 1,4-Dialdehydes

Conformationally constrained perhydroquinoxalines 4 show high κ receptor affinity, selectivity over related receptors and full agonistic activity. Since the κ affinity can be correlated with the dihedral angle of the ethylenediamine pharmacophore (4a: 55°/71°), the dihedral angles of the postulated cyclopentane derivative 5a (73°/84°) and indane derivative 6a (77°/81°) were calculated. The first step of the synthesis represents a double Henry reaction of 1,4-dialdehydes 8 and 10 with nitromethane, leading predominantly to the trans,trans-configured nitrodiols 9 and 11. X-ray crystal structure analyses of 9 and 11 led to dihedral angles O2 N−C−C−OH of 73.4 and 88.3°, respectively, which reflect the calculated dihedral angles of the hypothesized final products 5a and 6a.

Synthesis and pharmacological evaluation of 5-pyrrolidinylquinoxalines as a novel class of peripherally restricted κ-opioid receptor agonists

5-Pyrrolidinyl substituted perhydroquinoxalines were designed as conformationally restricted κ-opioid receptor agonists restricted to the periphery. The additional N atom of the quinoxaline system located outside the ethylenediamine κ pharmacophore allows the fine-tuning of the pharmacodynamic and pharmacokinetic properties. The perhydroquinoxalines were synthesized stereoselectively using the concept of late stage diversification of the central building blocks 14. In addition to high κ-opioid receptor affinity they demonstrate high selectivity over μ, δ, σ1, σ2, and NMDA receptors. In the [35S]GTPγS assay full agonism was observed. Because of their high polarity, the secondary amines 14a (log D7.4=0.26) and 14b (log D7.4=0.21) did not penetrate an artificial blood-brain barrier. 14b was able to inhibit the spontaneous pain reaction after rectal mustard oil application to mice (ED50=2.35 mg/kg). This analgesic effect is attributed to activation of peripherally located κ receptors, since 14b did not affect centrally mediated referred allodynia and hyperalgesia.