Design and Synthesis of New Transient Receptor Potential Vanilloid Type-1 (TRPV1) Channel Modulators: Identification, Molecular Modeling Analysis, and Pharmacological Characterization of the N-(4-Hydroxy-3-methoxybenzyl)-4-(thiophen-2-yl)butanamide, a Small Molecule Endowed with Agonist TRPV1 Activity and Protective Effects against Oxidative Stress

Insights from molecular dynamics simulations of TRPV1 channel modulators in pain

TRPV1 is a nonselective cation channel vital for detecting noxious stimuli (heat, acid, capsaicin). Its role in pain makes it a potential drug target for chronic pain management, migraines, and related disorders. This review updates molecular dynamics (MD) simulation studies on the TRPV1 channel, focusing on its gating mechanism, ligand-binding sites, and implications for drug design. The article also explores challenges in developing modulators, SAR optimization, and clinical trial studies. Efforts have been undertaken to concisely present MD simulation findings, with a focus on their relevance to drug discovery.

Synthesis and biological evaluation of capsaicin analogues as antioxidant and neuroprotective agents

Capsaicin and its analogues 3a-3q were designed and synthesized as potential new antioxidant and neuroprotective agents. Many analogues exhibited good antioxidant effects, and some showed more potent free radical scavenging activities than the positive drug quercetin (IC50 = 8.70 ± 1.75 μM for DPPH assay and 13.85 ± 2.87 μM for ABTS assay, respectively). The phenolic hydroxyl of capsaicin analogues was critical in determining antioxidant activity. Among these compounds, 3k displayed the most potent antioxidant activity. Cell vitality tests revealed that the representative compound 3k was good at protecting cells from H2O2-induced oxidative damage at low concentrations (cell viability increased to 90.0 ± 5.5% at 10 μM). In addition, the study demonstrated that 3k could reduce intracellular ROS accumulation and increase GSH levels to prevent H2O2-induced oxidative stress in SY5Y cells. In the mitochondrial membrane potential assay, 3k significantly increased the MMP level of SY5Y cells treated with H2O2 and played an anti-neuronal cell death role. These results provide a promising strategy to develop novel capsaicin analogues as potential antioxidant and neuroprotective agents.

In Silico-Guided Rational Drug Design and Synthesis of Novel 4-(Thiophen-2-yl)butanamides as Potent and Selective TRPV1 Agonists

We describe an in silico-guided rational drug design and the synthesis of the suggested ligands, aimed at improving the TRPV1-ligand binding properties and the potency of N-(4-hydroxy-3-methoxybenzyl)-4-(thiophen-2-yl) butanamide I, a previously identified TRPV1 agonist. The docking experiments followed by molecular dynamics simulations and thermodynamic analysis led the drug design toward both the introduction of a lipophilic iodine and a flat pyridine/benzene at position 5 of the thiophene nucleus. Most of the synthesized compounds showed high TRPV1 efficacy and potency as well as selectivity. The molecular modeling analysis highlighted crucial hydrophobic interactions between Leu547 and the iodo-thiophene nucleus, as in amide 2a, or between Phe543 and the pyridinyl moiety, as in 3a. In the biological evaluation, both compounds showed protective properties against oxidative stress-induced ROS formation in human keratinocytes. Additionally, while 2a showed neuroprotective effects in both neurons and rat brain slices, 3a exhibited potent antinociceptive effect in vivo..

Lipoic/Capsaicin-Related Amides: Synthesis and Biological Characterization of New TRPV1 Agonists Endowed with Protective Properties against Oxidative Stress

α-Lipoic acid is a sulfur-containing nutrient endowed with pleiotropic actions and a safe biological profile selected to replace the unsaturated alkyl acid of capsaicin with the aim of obtaining lipoic amides potentially active as a TRPV1 ligand and with significant antioxidant properties. Thus, nine compounds were obtained in good yields following a simple synthetic procedure and tested for their functional TRPV1 activity and radical-scavenger activity. The safe biological profile together with the protective effect against hypoxia damage as well as the in vitro antioxidant properties were also evaluated. Although less potent than capsaicin, almost all lipoic amides were found to be TRPV1 agonists and, specifically, compound 4, the lipoic analogue of capsaicin, proved to be the best ligand in terms of efficacy and potency. EPR experiments and in vitro biological assays suggested the potential protective role against oxidative stress of the tested compounds and their safe biological profile. Compounds 4, 5 and 9 significantly ameliorated the mitochondrial membrane potential caused by hypoxia condition and decreased F2-isoprostanes, known markers of oxidative stress. Thus, the experimental results encourage further investigation of the therapeutic potential of these lipoic amides.

Analgesic Effects of Lipid Raft Disruption by Sphingomyelinase and Myriocin via Transient Receptor Potential Vanilloid 1 and Transient Receptor Potential Ankyrin 1 Ion Channel Modulation

Transient Receptor Potential (TRP) Vanilloid 1 and Ankyrin 1 (TRPV1, TRPA1) cation channels are expressed in nociceptive primary sensory neurons, and integratively regulate nociceptor and inflammatory functions. Lipid rafts are liquid-ordered plasma membrane microdomains rich in cholesterol, sphingomyelin and gangliosides. We earlier showed that lipid raft disruption inhibits TRPV1 and TRPA1 functions in primary sensory neuronal cultures. Here we investigated the effects of sphingomyelinase (SMase) cleaving membrane sphingomyelin and myriocin (Myr) prohibiting sphingolipid synthesis in mouse pain models of different mechanisms. SMase (50 mU) or Myr (1 mM) pretreatment significantly decreased TRPV1 activation (capsaicin)-induced nocifensive eye-wiping movements by 37 and 41%, respectively. Intraplantar pretreatment by both compounds significantly diminished TRPV1 stimulation (resiniferatoxin)-evoked thermal allodynia developing mainly by peripheral sensitization. SMase (50 mU) also decreased mechanical hyperalgesia related to both peripheral and central sensitizations. SMase (50 mU) significantly reduced TRPA1 activation (formalin)-induced acute nocifensive behaviors by 64% in the second, neurogenic inflammatory phase. Myr, but not SMase altered the plasma membrane polarity related to the cholesterol composition as shown by fluorescence spectroscopy. These are the first in vivo results showing that sphingolipids play a key role in lipid raft integrity around nociceptive TRP channels, their activation and pain sensation. It is concluded that local SMase administration might open novel perspective for analgesic therapy.

RMD86, a thiophene derivative, promotes antinociceptive and antipyretic activities in mice

Treatment of pain and fever remains an important challenge for modern medicine. Non-steroidal anti-inflammatory drugs (NSAIDs) are the pharmacological options most often used, but their frequent use exposes the patient to serious side effects and dangerous drug interactions. In this context, thiophene derivatives are promising therapeutic alternatives. In this study, we evaluated the in vivo and in silico antinociceptive and antipyretic properties of RMD86, a thiophene derivative. At 100 mg/kg, RMD86 induced no significant changes in the motor coordination of mice in the Rotarod test. At 25, 50, and 100 mg/kg RMD86 significantly reduced the number of abdominal contortions induced by acetic acid (antinociceptive activity) in mice when compared to the control. In the formalin test, for the first phase, there was a reduction in licking times at doses of 50 and 100 mg/kg. In the second phase, reduction occurred at all doses. In the hot plate test, RMD86 (at 100 mg/kg) increased latency time in the first 30 min. For antipyretic activity, RMD86, when compared to the reference drug acetaminophen (250 mg/kg), significantly reduced pyrexia at 30, 60, and 120 min, at dosages of 25, 50 and 100 mg/kg. Molecular docking studies revealed that RMD86 presents a greater number of interactions and lower energy values than both the co-crystallized ligand and the reference drug (meloxicam) against COX-1 and COX-2 isoenzymes. The results give evidence of the analgesic and antipyretic properties like NSAIDs suggesting its potential for pain therapy.

Design, synthesis and pharmacological evaluation of ester-based quercetin derivatives as selective vascular KCa1.1 channel stimulators

Quercetin represents one of the most studied dietary flavonoids; it exerts a panel of pharmacological activities particularly on the cardiovascular system. Stimulation of vascular K_Ca1.1 channels contributes to its vasorelaxant activity, which is, however, counteracted in part by its concomitant stimulation of Ca_V1.2 channels. Therefore, several quercetin hybrid derivatives were designed and synthesized to produce a more selective K_Ca1.1 channel stimulator, then assessed both in silico and in vitro. All the derivatives interacted with the K_Ca1.1 channel with similar binding energy values. Among the selected derivatives, 1E was a weak vasodilator, though displaying an interesting Ca_V1.2 channel blocking activity. The lipoyl derivatives 1F and 3F, though showing pharmacological and electrophysiological features similar to those of quercetin, seemed to be more effective as K_Ca1.1 channel stimulators as compared to the parent compound. The strategy pursued demonstrated how different chemical substituents on the quercetin core can change/invert its effect on Ca_V1.2 channels or enhance its K_Ca1.1 channel stimulatory activity, thus opening new avenues for the synthesis of efficacious vasorelaxant quercetin hybrids.

Design, Synthesis and In Vitro Experimental Validation of Novel TRPV4 Antagonists Inspired by Labdane Diterpenes

Labdane diterpenes are widespread classes of natural compounds present in variety of marine and terrestrial organisms and plants. Many of them represents “natural libraries” of compounds with interesting biological activities due to differently functionalized drimane nucleus exploitable for potential pharmacological applications. The transient receptor potential channel subfamily V member 4 (TRPV4) channel has recently emerged as a pharmacological target for several respiratory diseases, including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Inspired by the labdane-like bicyclic core, a series of homodrimane-derived esters and amides was designed and synthesized by modifying the flexible tail in position 1 of (+)-sclareolide, an oxidized derivative of the bioactive labdane-type diterpene sclareol. The potency and selectivity towards rTRPV4 and hTRPV1 receptors were assessed by calcium influx cellular assays. Molecular determinants critical for eliciting TRPV4 antagonism were identified by structure-activity relationships. Among the selective TRPV4 antagonists identified, compound 6 was the most active with an IC₅₀ of 5.3 μM. This study represents the first report of semisynthetic homodrimane TRPV4 antagonists, selective over TRPV1, and potentially useful as pharmacological tools for the development of novel TRPV4 channel modulators.

3-Amino-alkylated indoles: unexplored green products acting as anti-inflammatory agents

Aim: Over the years, indole has proved to be a versatile scaffold for the design of molecules acting as anti-inflammatory agents. Materials & Methods: A small library of 3-amino-alkylated indoles has been obtained by an optimized Mannich green approach. The anti-inflammatory activity of the new 3-amino-alkylated indoles, GLYC 0–10, was evaluated in RAW 264.7 macrophages. Results: The anti-inflammatory activity of the new 3-amino-alkylated indoles, GLYC 0–10, was evaluatedn and, among them, GLYC 4, 5 and 9 displayed the greatest inhibitory effects on nitric oxide production, with IC50 values of 5.41, 4.22 and 6.3 μM, respectively. Conclusion: Our outcomes, overall, highlight the importance of the indole substitution in the anti-inflammatory activity of these compounds, exerted by acting on the interlinked NF-κB/ERK1/2 pathways.

Primary Benzylamines by Efficient N-Alkylation of Benzyl Alcohols Using Commercial Ni Catalysts and Easy-to-Handle Ammonia Sources

Primary benzylamines are highly important building blocks in the pharmaceutical and polymer industry. An attractive catalytic approach to access these compounds is the direct coupling of benzyl alcohols with ammonia via the borrowing hydrogen methodology. However, this approach is usually hampered by a series of side-reactions, one of the most prominent being the overalkylation of the formed primary amine. Herein, we describe a robust catalytic methodology, which utilizes commercially available heterogeneous Ni catalysts and easy-to-handle ammonia sources, such as aqueous ammonia or ammonium salts, for the formation of primary benzylamines with good selectivity and scope. Notably, our method enables the conversion of potentially lignin-derived vanillyl alcohol to vanillylamine, which can be used to produce emerging biobased polymers or as pharma building blocks. Important sugar derived platform alcohols as well as long chain aliphatic primary alcohols can be successfully aminated. Moreover, we provide an alternative, sustainable route to p-xylylenediamine and m-xylylenediamine, important components of heat resistant polyamides such as Kevlar.

Antioxidant and Anti-Inflammatory Activities of Flavanones from Glycyrrhiza glabra L. (licorice) Leaf Phytocomplexes: Identification of Licoflavanone as a Modulator of NF-kB/MAPK Pathway

Inflammation represents an adaptive response generated by injuries or harmful stimuli. Natural remedies represent an interesting alternative to traditional therapies, involving several biochemical pathways. Besides, the valorization of agrochemical wastes nowadays seems to be a feasible way to reduce the health spending and improve the accessibility at bioactive natural compounds. In this context, the chemical composition of three Glycyrrhiza glabra L. (licorice) leaf extracts, obtained through maceration or ultrasound-assisted method (fresh and dried leaves) was investigated. A guided fractionation obtained three main components: pinocembrin, glabranin and licoflavanone. All the extracts showed similar antioxidant properties, evaluated by 2,2′-diphenyl-1-picrylhydrazyl (DPPH) or 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) Diammonium Salt (ABTS) assay, while, among the isolated compounds, licoflavanone exhibited the best antioxidant activity. The anti-inflammatory activity of the extracts and the purified compounds was investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. Extract C and licoflavanone showed a good anti-inflammatory activity without affecting cell viability, as they decreased nitrite levels even when used at 12.5 μg/mL (p < 0.005) and 50 μM concentration (p < 0.001), respectively. Interestingly, licoflavanone markedly decreased pro-inflammatory cytokines and cyclooxygenase 2/inducible nitric oxide synthase (COX-2/iNOS) expression levels (p < 0.001). A modulation of nuclear factor kappa B/mitogen-activated protein kinases (NF-kB/MAPK) pathway underlay such behavior, highlighting the potential of this natural compound as a new scaffold in anti-inflammatory drug research.

Rational drug design and synthesis of new α-Santonin derivatives as potential COX-2 inhibitors

Sesquiterpene compounds are widely known for their numerous pharmacological activities. Herein the focus of the authors was on α-Santonin, a sesquiterpene lactone from the Artemisia genus: the aim was to determine whether α-Santonin could be considered in the treatment of inflammation and pain. To this purpose, a small series of derivatives was designed and screened in silico against the enzyme COX-2 along with the parent compound. Drug-likeness parameters were also assessed. The compounds were eventually synthesized, and few were tested to determine their efficacy in the inhibition of COX-2 activity and expression. Overall, compound A2 was the only one with a detectable inhibitory potential of COX-2 activity whilst two of its ether derivatives demonstrated improved ability in the inhibition of COX-2 expression.

Tricyclic Spirolactones as Modular TRPV1 Synthetic Agonists

TRPV1 is a prominent signal integrator of the pain system, known to be activated by vanilloids, a family of endogenous and exogenous pain-evoking molecules, through the vanilloid-binding site (VBS). The extensive preclinical profiling of small molecule inhibitors provides intriguing evidence that TRPV1 inhibition can be a useful therapeutic approach. However, the dissimilarity of chemical species that activate TRPV1 creates a major obstacle to understanding the molecular mechanism of pain induction, which is viewed as a pivotal trait of the somatosensory system. Here, we establish the existence of a unique family of synthetic agonists that interface with TRPV1 through the VBS, containing none of the molecular domains previously believed to be required for this interaction. The overarching value obtained from our inquiry is the novel advancement of the existing TRPV1 activation model. These findings uncover new potential in the area of pain treatment, providing a novel synthetic platform.

Structure-activity relationships for the synthesis of selective cyclooxygenase 2 inhibitors: an overview (2009-2016)

Most drugs used to treat pain and inflammation act through inhibition of the enzymes prostaglandin G/H synthase, commonly known as cyclooxygenase (COX). Among these, the simultaneous inhibition of cyclooxygenase 1 (COX-1) would explain the unwanted side effects in the gastrointestinal tract and many adverse cardiovascular effects, such as high blood pressure, myocardial infarction and thrombosis. These side effects led in time to the development of NSAIDs that behave as selective COX-2 inhibitors. This manuscript highlights the structure-activity relationships which characterize the chemical scaffolds endowed with selective COX-2 inhibition. Additionally, the role of COX-2 inhibitors in the pain phenomenon and cancer is discussed.

Castanea sativa Mill. Bark Extract Protects U-373 MG Cells and Rat Brain Slices Against Ischemia and Reperfusion Injury

Ischemic brain injury is one of the most important causes of death worldwide. The use of one-drug-multi-target agents based on natural compounds is a promising therapeutic option for cerebral ischemia due to their pleiotropic properties. This study assessed the neuroprotective properties of Castanea sativa Mill. bark extract (ENC) in human astrocytoma U-373 MG cells subjected to oxygen-glucose deprivation and reperfusion and rat cortical slices subjected to ischemia-like conditions or treated with glutamate or hydrogen peroxide. Neuroprotective effects were determined by assessing cells or slices viability (MTT assay), ROS formation (DCFH-DA assay), apoptosis (sub G0/G1 peak), nuclear fragmentation and chromatin condensation (DAPI staining) as well as changes in lysosomes and mitochondria morphology (Acridine Orange and Rhodamine123 staining, respectively). ENC treatment before injury on U-373 MG cells (5-50 μg/ml) and cortical slices (50-100 μg/ml) provided neuroprotection, while lower or higher concentrations (100 μg/ml U-373 MG cells, 200 μg/ml brain slices) were ineffective. ENC addition during reperfusion or after the injury was not found to be effective. The results suggest that ENC might hold potential as preventive neuroprotective agent, and indicate the importance of further studies exploring its mechanism of action. J. Cell. Biochem. 118: 839-850, 2017. © 2016 Wiley Periodicals, Inc.

Synthesis and biological evaluation of a new class of benzothiazines as neuroprotective agents

Neurodegenerative diseases are disorders related to the degeneration of central neurons that gradually lead to various, severe alterations of cognitive and/or motor functions. Currently, for no such diseases does any pharmacological treatment exist able to arrest its progression. Riluzole (1) is a small molecule able to interfere with multiple cellular and molecular mechanisms of neurodegeneration, and is the only approved treatment of amyotrophic lateral sclerosis (ALS), the progression of which proved to significantly slow, thus increasing somewhat average survival. Here we report the synthesis of differently functionalized 4H-3,1-benzothiazine (5-6) and 2H-1,4-benzothiazine (7) series as superior homologues of 1. Biological evaluation demonstrated that amidine 4H-3,1-benzothiazine derivatives 5b-d can reduce glutamate and LDH release in the oxygen/glucose deprivation and reperfusion model (OGD/R) applied to brain slices with a higher potency than 1. Moreover the mentioned compounds significantly reduce glutamate- and 6-hydroxydopamine (6-OHDA)-induced cytotoxicity in neuroblastoma cells. In addition, the same compounds limit ROS formation in both neuronal preparations. Finally, 5c proved effective in inhibiting neuronal voltage-dependent Na⁺ and Ca²⁺-channels, showing a profile comparable with that of 1.