Synthesis and investigations of double-pharmacophore ligands for treatment of chronic and neuropathic pain

Fentanyl Structure as a Scaffold for Opioid/Non-Opioid Multitarget Analgesics

One of the strategies in the search for safe and effective analgesic drugs is the design of multitarget analgesics. Such compounds are intended to have high affinity and activity at more than one molecular target involved in pain modulation. In the present contribution we summarize the attempts in which fentanyl or its substructures were used as a μ-opioid receptor pharmacophoric fragment and a scaffold to which fragments related to non-opioid receptors were attached. The non-opioid ‘second’ targets included proteins as diverse as imidazoline I₂ binding sites, CB₁ cannabinoid receptor, NK₁ tachykinin receptor, D₂ dopamine receptor, cyclooxygenases, fatty acid amide hydrolase and monoacylglycerol lipase and σ₁ receptor. Reviewing the individual attempts, we outline the chemistry, the obtained pharmacological properties and structure-activity relationships. Finally, we discuss the possible directions for future work.

Transition-Metal-Free Valorization of Biomass-derived Levulinic Acid Derivatives: Synthesis of Curcumene and Xanthorrhizol

Levulinic acid (LA) is acknowledged one of the most promising biomass-derived platform molecules and can be transformed into various value-added chemicals. Here, we report a new reaction process for the valorization of LA derivatives under transition-metal-free condition. The protocol combined with the conversion of the levulinate to tosylhydrazone and base promoted arylation, acylation, and etherification cross-coupling. Moreover, our method was applied to synthesize three biologically active molecules, rac-curcumene, rac-xanthorrhizol and rac-4,7-dimethyl-l-tetralone. This reaction discloses a new avenue for the high-value utilization of platform molecules.

Molecular mechanisms of fentanyl mediated β-arrestin biased signaling

The development of novel analgesics with improved safety profiles to combat the opioid epidemic represents a central question to G protein coupled receptor structural biology and pharmacology: What chemical features dictate G protein or β-arrestin signaling? Here we use adaptively biased molecular dynamics simulations to determine how fentanyl, a potent β-arrestin biased agonist, binds the μ-opioid receptor (μOR). The resulting fentanyl-bound pose provides rational insight into a wealth of historical structure-activity-relationship on its chemical scaffold. Following an in-silico derived hypothesis we found that fentanyl and the synthetic opioid peptide DAMGO require M153 to induce β-arrestin coupling, while M153 was dispensable for G protein coupling. We propose and validate an activation mechanism where the n-aniline ring of fentanyl mediates μOR β-arrestin through a novel M153 “microswitch” by synthesizing fentanyl-based derivatives that exhibit complete, clinically desirable, G protein biased coupling. Together, these results provide molecular insight into fentanyl mediated β-arrestin biased signaling and a rational framework for further optimization of fentanyl-based analgesics with improved safety profiles.

The global opioid crisis has drawn significant attention to the risks associated with over-use of synthetic opioids. Despite the public attention, and perhaps in-line with the profit-based incentives of the pharmaceutical industry, there is no public structure of mu-opioid receptor bound to fentanyl or fentanyl derivatives. A publicly available structure of the complex would allow open-source development of safer painkillers and synthetic antagonists. Current overdose antidotes, antagonists, require natural products in their synthesis which persists a sizable barrier to market and develop better antidotes. In this work we use advance molecular dynamics techniques to obtain the bound geometry of mu-opioid receptor with fentanyl (and derivatives) and uncovered a novel molecular switch involved in receptor activation. Based on our in-silico structure, we synthesized and tested novel compounds to validate our predicted structure. Herein we report the bound state of several dangerous fentanyl derivatives and introduce new derivatives with signaling profiles that may lead to lower risk of respiratory depression.

Fentanyl Family at the Mu-Opioid Receptor: Uniform Assessment of Binding and Computational Analysis

Interactions of 21 fentanyl derivatives with μ-opioid receptor (μOR) were studied using experimental and theoretical methods. Their binding to μOR was assessed with radioligand competitive binding assay. A uniform set of binding affinity data contains values for two novel and one previously uncharacterized derivative. The data confirms trends known so far and thanks to their uniformity, they facilitate further comparisons. In order to provide structural hypotheses explaining the experimental affinities, the complexes of the studied derivatives with μOR were modeled and subject to molecular dynamics simulations. Five common General Features (GFs) of fentanyls' binding modes stemmed from these simulations. They include: GF1) the ionic interaction between D147 and the ligands' piperidine NH⁺ moiety; GF2) the N-chain orientation towards the μOR interior; GF3) the other pole of ligands is directed towards the receptor outlet; GF4) the aromatic anilide ring penetrates the subpocket formed by TM3, TM4, ECL1 and ECL2; GF5) the 4-axial substituent (if present) is directed towards W318. Except for the ionic interaction with D147, the majority of fentanyl-μOR contacts is hydrophobic. Interestingly, it was possible to find nonlinear relationships between the binding affinity and the volume of the N-chain and/or anilide's aromatic ring. This kind of relationships is consistent with the apolar character of interactions involved in ligand⁻receptor binding. The affinity reaches the optimum for medium size while it decreases for both large and small substituents. Additionally, a linear correlation between the volumes and the average dihedral angles of W293 and W133 was revealed by the molecular dynamics study. This seems particularly important, as the W293 residue is involved in the activation processes. Further, the Y326 (OH) and D147 (Cγ) distance found in the simulations also depends on the ligands' size. In contrast, neither RMSF measures nor D114/Y336 hydrations show significant structure-based correlations. They also do not differentiate studied fentanyl derivatives. Eventually, none of 14 popular scoring functions yielded a significant correlation between the predicted and observed affinity data (R < 0.30, n = 28).

Fentanyl-related compounds and derivatives: current status and future prospects for pharmaceutical applications

Fentanyl and its analogs have been mainstays for the treatment of severe to moderate pain for many years. In this review, we outline the structural and corresponding synthetic strategies that have been used to understand the structure-biological activity relationship in fentanyl-related compounds and derivatives and their biological activity profiles. We discuss how changes in the scaffold structure can change biological and pharmacological activities. Finally, recent efforts to design and synthesize novel multivalent ligands that act as mu and delta opioid receptors and NK-1 receptors are discussed.

Synthesis and biological evaluation of new opioid agonist and neurokinin-1 antagonist bivalent ligands

Newly designed bivalent ligands-opioid agonist/NK1-antagonists have been synthesized. The synthesis of new starting materials-carboxy-derivatives of Fentanyl (1a-1c) was developed. These products have been transformed to 'isoimidium perchlorates' (2a-c). The new isoimidium perchlorates have been successfully implemented in nucleophilic addition reactions, with l-tryptophan 3,5-bis(trifluoromethyl)benzyl ester to give the target compounds-amides (3a-c). Perchlorates (2a-c) successfully undergo reactions with other nucleophiles such as alcohols, amines or hydrazines. The obtained compound 3b exhibited μ-opioid agonist activity and NK1-antagonist activity and may serve as a useful lead compound for the further design of a new series of opioid agonist/NK1-antagonist compounds.

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.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Synthesis and Crystallographic Study of N'-(1-benzylpiperidin-4-yl)acetohydrazide

As part of a study into new Fentanyl-derived opioid compounds with potent analgesic activity and reduced side effects the starting material title compound, C₁₄H₂₁N₃O (1), was synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The crystal structure is monoclinic Cc with unit cell parameters a = 14.1480(3) Å, b = 14.1720(4) Å, c = 27.6701(7) Å, β = 96.956(1)°, α = γ = 90°. The compound has crystallized with four crystallographically unique molecules in the asymmetric unit; each molecule has a very similar conformation and an analysis of the structure shows that although all four unique molecules overlay very well there is no evidence of pseudo-symmetry which would relate the molecules in the higher symmetry space group C2/c. The crystal packing consists of two separate hydrogen bonded chains which are linked together to form a thick 2D structure in the ab plane.

Proton sharing and transfer in some zwitterionic compounds based on 4-oxo-4-((1-phenethylpiperidin-4-yl)(phenyl)amino)alcanoic acids

Three compounds, each derived from Fentanyl and differing essentially only in the length of a carboxylic acid chain, were synthesized and yielded four crystal structures three of which share several structural similarities, including the length of the chain, while the fourth, with a shorter chain, is quite different. The chain length has a significant influence on the crystal structures formed. The 'three atom' chain compounds are all solvated zwitterions which feature a hydrogen-bonded 'dimer' between adjacent zwitterions. The formation of this large dimer leaves available a second carboxylate O atom to take part in hydrogen bonding interactions with solvent molecules. The shorter 'two atom' chain compound was difficult to crystallize and required the use of synchrotron radiation to measure X-ray diffraction data. It does not form the same dimer motif observed in the 'three atom' chain compounds and has not formally formed a zwitterion; although there is evidence of proton sharing or disorder X-ray data are insufficient to create a disordered model, and the compound was modeled as formally neutral based on O-H and N-H distances. Room temperature analyses showed the proton transfer behavior to be independent of crystal temperature, and nuclear magnetic resonance studies show proton transfer behavior in solution. The formation of a zwitterionic hydrogen-bonded dimer is implicated in providing some stability during crystal growth of the easily crystallized 'three atom' chain compounds.