Synthesis and Biological Evaluation of Pyridine-Containing Lipoxin A4Analogues

A general synthesis of aromatic and heteroaromatic lipoxin B4 analogues

Lipoxins are an important class of pro-resolving mediators that play a crucial role in the resolution of inflammation. Thus, the synthesis of more chemically and metabolically stable synthetic lipoxin analogues is an area of significant interest. Whereas synthetic analogues of lipoxin A4 (LXA4) have been well studied, analogues of lipoxin B4 (LXB4) have been the focus of considerably less attention. Herein we report the asymmetric synthesis of a focused library of LXB4 mimetics in which the triene core of the molecule has been replaced with different aromatic and heteroaromatic rings. The synthesis of each of these analogues was achieved by a general strategy in which the key steps were a Suzuki cross coupling between a common upper chain fragment and an aromatic lower chain, followed by a stereoselective ketone reduction.

Synthesis of Polysubstituted Pyridines and Pyrazines via Truce-Smiles Rearrangement of Amino Acid-Based 4-Nitrobenzenesulfonamides

Immobilized l-glutamic acid β-methyl ester was sulfonylated with 4-nitrobenzenesulfonyl chloride and alkylated with various α-haloketones. The resulting sulfonamides were reacted with potassium trimethylsilanolate. Then, upon cleavage from the polymer support, tetrasubstituted pyridines were produced as the result of one-step C-arylation, aldol condensation, and oxidation. When cleavage from the resin occurred before the trimethylsilanolate treatment, C-arylation was followed by enamination, which yielded trisubstituted pyrazines. Through the developed protocols, targeted synthesis of novel heterocyclic derivatives was performed using mild reaction conditions and a number of readily available starting materials.

Posing the rationale for synthetic lipoxin mimetics as an adjuvant treatment to gold standard atherosclerosis therapies

Atherosclerosis is a progressive, multifactorial inflammatory, and dyslipidaemic disease, responsible for the majority of cardiovascular diseases globally. The chronic inflammation is the main driver of the initiation and progression of such disease, as a result of an imbalanced lipid metabolism and an ineffective immune response to attenuate the inflammatory component. The importance of inflammation resolution is being increasingly recognised in atherosclerosis and cardiovascular disease. It has a complex mechanism consisting of multiple stages, including restoring an effective removal of apoptotic bodies (efferocytosis) and their degradation (effero-metabolism), a macrophage phenotype switching towards resolving phenotypes, and the promotion of tissue healing and regeneration. The low-grade inflammation associated with atherosclerosis development is a driving force in disease exacerbation, and hence inflammation resolution is a key area of research. In this review, we explore the complex disease pathogenesis and its many contributing factors to gain a greater understanding of the disease and identify the current and potential therapeutic targets. First-line treatments and their efficacy will also be discussed in detail, to highlight the emerging field of resolution pharmacology. Despite the great efforts made by current gold-standard treatments, such as lipid-lowering and glucose-lowering drugs, they remain ineffective at tackling residual inflammatory risk and residual cholesterol risk. Resolution pharmacology represents a new era of atherosclerosis therapy, as endogenous ligands associated with inflammation resolution are exploited for their pharmacological benefits in a more potent and longer-acting manner. Novel FPR2-agonists, such as synthetic lipoxin analogues, provide an exciting new approach to enhance the pro-resolving response of the immune system and subsequently end the pro-inflammatory response to allow for an anti-inflammatory and pro-resolving environment for tissue healing, regeneration, and return to homeostasis.

One-Pot Sequential Hydroamination Protocol for N-Heterocycle Synthesis: One Method To Access Five Different Classes of Tri-Substituted Pyridines

Tri-substituted pyridines are important scaffolds that can be found in a plethora of commercially available drugs. A one-pot general method for the selective synthesis of less explored/challenging patterns of tri-substituted pyridines is described. Hydroamination of alkynes with commercially available N-triphenylsilylamine generates N-silylenamines. These in situ generated N-silylenamines, upon reaction with α,β-unsaturated carbonyl compounds and subsequent oxidation, furnish 25 examples of selectively substituted 2,4,5-, 2,3,4-, 3,4,5-, 2,3,5-, and 2,3,6-trisubstituted pyridines in up to 78% yield. The reaction features high functional group compatibility providing an expeditious and general approach for the assembly of selectively substituted tri-substituted pyridine derivatives. The robustness and practicality of the reaction have been demonstrated in a gram-scale reaction.

Lipoxin Mimetics and the Resolution of Inflammation

Inflammation and its timely resolution are critical to ensure effective host defense and appropriate tissue repair after injury and or infection. Chronic, unresolved inflammation typifies many prevalent pathologies. The key mediators that initiate and drive the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. More recently, there is a growing appreciation that specific mediators, including arachidonate-derived lipoxins, are generated in self-limiting inflammatory responses to promote the resolution of inflammation and endogenous repair mechanisms without compromising host defense. We discuss the proresolving biological actions of lipoxins and recent efforts to harness their therapeutic potential through the development of novel, potent lipoxin mimetics generated via efficient, modular stereoselective synthetic pathways. We consider the evidence that lipoxin mimetics may have applications in limiting inflammation and reversing fibrosis and the underlying mechanisms.

Development of synthetic lipoxin-A4 mimetics (sLXms): New avenues in the treatment of cardio-metabolic diseases

Resolution of inflammation is a complex, dynamic process consisting of several distinct processes, including inhibition of endothelial activation and leukocyte trafficking; promotion of inflammatory cell apoptosis and subsequent non-phlogistic scavenging and degradation; augmentation of pathogen phagocytosis; modulation of stromal cell phenotype coupled to the promotion of tissue regeneration and repair. Among these tightly regulated processes, the clearance and degradation of apoptotic cells without eliciting an inflammatory response is a crucial allostatic mechanism vital to developmental processes, host defence, and the effective resolution of inflammation. These efferocytic and subsequent effero-metabolism processes can be carried out by professional and non-professional phagocytes. Defective removal or inadequate processing of apoptotic cells leads to persistent unresolved inflammation, which may promote insidious pathologies including scarring, fibrosis, and eventual organ failure. In this manuscript, the well-established role of endothelial activation and leukocyte extravasation, as classical vascular targets of the 'inflammation pharmacology', will be briefly reviewed. The main focus of this work is to bring attention to a less explored aspect of the 'resolution pharmacology', aimed at tackling defective efferocytosis and inefficient effero-metabolism, as key targeted mechanisms to prevent or pre-empt vascular complications in cardio-metabolic diseases. Despite the use of gold standard lipid-lowering drugs or glucose-lowering drugs, none of them are able to tackle the so called residual inflammatory risk and/or the metabolic memory. In this review, the development of synthetic mimetics of endogenous mediators of inflammation is highlighted. Such molecules finely tune key components across the whole inflammatory process, amongst various other novel therapeutic paradigms that have emerged over the past decade, including anti-inflammatory therapy. More specifically, FPR2-agonists in general, and Lipoxin analogues in particular, greatly enhance the reprogramming and cross-talk between classical and non-classical innate immune cells, thus inducing both termination of the pro-inflammatory state as well as promoting the subsequent resolving phase, which represent pivotal mechanisms in inflammatory cardio-metabolic diseases.

Synthesis and Biological Evaluation of Bicyclo[1.1.1]pentane-Containing Aromatic Lipoxin A4 Analogues

Lipoxins are important drivers of inflammation resolution, suggesting a potential therapeutic benefit. Bicyclo[1.1.1]pentanes (BCPs) are potential isosteric replacements for arenes and/or alkyl groups within drug candidates. We carried out an asymmetric synthesis of four BCP-containing synthetic lipoxin A₄ mimetics (BCP-sLXms) in which the key steps were a Suzuki coupling, an asymmetric ketone reduction, and a triethylborane-initiated radical bicyclopentylation. These mimetics were screened for their impact on inflammatory responses, and one imidazolo-BCP-sLXm (6a) was found to possess high anti-inflammatory activity.

Synthesis of aromatic lactone analogues of Lipoxin A4

Objective

Synthesis of novel aromatic Lipoxin A4 lactone analogues.

Results

Novel para-substituted aromatic lactone analogues of Lipoxin A4 have been synthesized in a convergent manner with six steps in the longest linear sequence in 12–13% yields, employing 2-deoxy-d-ribose as a chiral pool starting material and the classical E-selective Wittig olefination.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-022-05917-4.

Asymmetric Synthesis and Biological Screening of Quinoxaline-Containing Synthetic Lipoxin A4 Mimetics (QNX-sLXms)

Failure to resolve inflammation underlies many prevalent pathologies. Recent insights have identified lipid mediators, typified by lipoxins (LXs), as drivers of inflammation resolution, suggesting potential therapeutic benefit. We report the asymmetric preparation of novel quinoxaline-containing synthetic-LXA₄-mimetics (QNX-sLXms). Eight novel compounds were screened for their impact on inflammatory responses. Structure–activity relationship (SAR) studies showed that (R)-6 (also referred to as AT-02-CT) was the most efficacious and potent anti-inflammatory compound of those tested. (R)-6 significantly attenuated lipopolysaccharide (LPS)- and tumor-necrosis-factor-α (TNF-α)-induced NF-κB activity in monocytes and vascular smooth muscle cells. The molecular target of (R)-6 was investigated. (R)-6 activated the endogenous LX receptor formyl peptide receptor 2 (ALX/FPR2). The anti-inflammatory properties of (R)-6 were further investigated in vivo in murine models of acute inflammation. Consistent with in vitro observations, (R)-6 attenuated inflammatory responses. These results support the therapeutic potential of the lead QNX-sLXm (R)-6 in the context of novel inflammatory regulators.

G-Protein Coupled Receptors Involved in the Resolution of Inflammation: Ligands and Therapeutic Perspectives

Dysregulated inflammation is a central pathological process in diverse disease states, including neurodegenerative disorders. The recent concept of "resolution of inflammation" is offering a conceptual change for the diagnosis and the development of new therapeutic approaches for chronic inflammatory diseases. Resolution of inflammation terminates the inflammatory response promoting the return to tissue homeostasis through the action of several classes of mediators, termed specialized pro-resolving lipid mediators (SPMs), that include lipoxins, resolvins, protectins, and maresins. SPMs provide "stop signals" that reduce the number of immune cells at the site of insult and increase the clearance of apoptotic cells through phagocytosis. SPMs elicit their effects through the interaction with specific G-protein coupled receptors (GPCRs). The elucidation of the pathways downstream of the GPCRs involved in the resolution of chronic inflammation is opening novel opportunities to generate novel anti-inflammatory agents. This review focuses on the SPMs and the receptors through which their effects are mediated. The medicinal chemistry of the modulators of the GPCRs involved in the resolution of inflammation will be illustrated, by highlighting the potential for developing new antiinflammatory drugs.

Metal-free multicomponent reactions: a benign access to monocyclic six-membered N-heterocycles

The advent of multicomponent reactions in the synthesis of heterocycles and their ever burgeoning applications in drug development, materials chemistry, and catalysis, have attracted a great deal of current scientific interest. In particular, the metal-free multicomponent synthesis of six membered N-heterocycles has undergone intensive research over the last two decades offering an environmentally benevolent means contrary to traditional metal catalysed reactions. To the best of our knowledge, there exists no exclusive review on the metal-free multicomponent synthesis of six membered N-heterocyles, and hence the present report highlights the progress on metal-free multicomponent reactions with their advantages and mechanistic insights to access monocyclic six-membered N-heterocycles including pyridine, pyrimidine, pyrazine, triazine and their hydrogenated derivatives. The literature is covered since 2000, and the contents offer not only striking methods for divergent synthesis of six-membered N-heterocycles but also put forward some new insights into the exploration of metal-free multicomponent chemistry.

Therapeutic potential of the FPR2/ALX agonist AT-01-KG in the resolution of articular inflammation

The resolution of inflammation is a dynamic process, characterized by the biosynthesis of pro-resolving mediators, including the lipid Lipoxin A4 (LXA₄). LXA₄ acts on the N-formyl peptide receptor 2 (FPR2/ALX) to mediate anti-inflammatory and pro-resolving effects. In order to exploit the therapeutic potential of endogenous LXA₄ in the context of inflammation we have recently developed synthetic LXA₄ mimetics (sLXms) including a dimethyl-imidazole-containing FPR2/ALX agonist designated AT-01-KG. Here, we have investigated the effect of treatment with AT-01-KG in established models of articular inflammation. In a model of gout, mice were injected with MSU crystals and treated with AT-01-KG at the peak of inflammatory response. The treatment decreased the number of neutrophils in the knee exudate, an effect which was accompanied by low levels of myeloperoxidase, CXCL1 and IL-1β in periarticular tissue. AT-01-KG treatment led to reduced tissue damage and hypernociception. The effects of AT-01-KG on neutrophil accumulation were not observed in MSU treated FPR2/3^-/-mice. Importantly, AT-01-KG induced resolution of articular inflammation by increasing neutrophil apoptosis and subsequent efficient efferocytosis. In a model of antigen-induced arthritis, AT-01-KG treatment also attenuated inflammatory responses. These data suggest that AT-01-KG may be a potential new therapy for neutrophilic inflammation of the joints.

Synthesis of Polysubstituted Trifluoromethylpyridines from Trifluoromethyl-α,β-ynones

A novel and efficient method for synthesis of polysubstituted trifluoromethylpyridine derivatives by the Bohlmann-Rahtz heteroannulation reaction is described, which use trifluoromethyl-α,β-ynones as trifluoromethyl building blocks to react with β-enamino esters or β-enamino ketones in the presence of ZnBr₂ to form the trifluoromethylpyridine derivatives in good yields. The protocol has the advantages of readily available starting materials, mild reaction conditions, and high atom economy.

Pro-resolving lipid mediators: Agents of anti-ageing?

Inflammation is an essential response to injury and its timely and adequate resolution permits tissue repair and avoidance of chronic inflammation. Ageing is associated with increased inflammation, sub-optimal resolution and these act as drivers for a number of ageing-associated pathologies. We describe the role played by specialised proresolving lipid mediators (SPMs) in the resolution of inflammation and how insufficient levels of these mediators, or compromised responsiveness may play a role in the pathogenesis of many ageing-associated pathologies, e.g. Alzheimer's Disease, atherosclerosis, obesity, diabetes and kidney disease. Detailed examination of the resolution phase of inflammation highlights the potential to harness these lipid mediators and or mimetics of their bioactions, in particular, their synthetic analogues to promote effective resolution of inflammation, without compromising the host immune system.

Consecutive three- and four-component coupling-Bagley-Bohlmann-Rahtz syntheses of tri- and tetrasubstituted pyridines

The concatenation of the modified Sonogashira alkynone synthesis and the Bagley-Bohlmann-Rahtz pyridine synthesis gives novel consecutive three- and four-component coupling-Bagley-Bohlmann-Rahtz (cBBR) syntheses of tri- and tetrasubstituted pyridines in a one-pot fashion. With these processes 15 differently substituted 3-ethoxycarbonyl 2-methylpyridines can be readily obtained in modest to moderate yields.

Metal-free oxidative cyclization of acetophenones with diamines: a facile access to phenylpyridines

An efficient metal-free access to 2- and 3-phenylpyridines via oxidative coupling of acetophenones with 1,3-diaminopropane has been described.

Visible light-induced aerobic C–N bond activation: a photocatalytic strategy for the preparation of 2-arylpyridines and 2-arylquinolines

An efficient method for accessing arylpyridines and arylquinolines via visible light-induced aerobic C–N bond activation is described.

Regioselective Pd-Catalyzed Synthesis of 2,3,6-Trisubstituted Pyridines from Isoxazolinones

Substituted pyridines are prevalent heterocycles of fundamental importance. Their efficient regioselective preparation is often still a challenge despite a large number of reported synthetic methodologies. In this letter we report an operationally simple approach that makes use of readily accessible isoxazolinones. The protocol involves a Pd(II)-catalyzed C-regioselective 1,4-addition to vinylketones, followed by a Pd(0)-catalyzed transformation, which is assumed to proceed via vinylnitrene-Pd intermediates. Both hydrogen and air are necessary for the pyridine formation step and could be employed at ratios above the upper explosive limit thus avoiding a safety issue. This new strategy allows an effective, scalable and practical access to various previously unknown 2,3,6-trisubstituted pyridines.

A mild and facile synthesis of polyfunctionalized pyridines: merging three-component cyclization and aerobic oxidation by amine/metal catalysts

A mild and facile synthesis of polyfunctionalized pyridines from NH₄OAc, β,γ-unsaturated α-ketoesters, and ketones/aldehydes has been reported through tandem three-component cyclization and aerobic oxidation using the combination of amine and metal catalysts.

Expedient, catalyst-free, three-component synthesis of fused tetrahydropyridines in water

An expedient, three-component synthesis of oxazolo[3,2-a]pyridines and pyrido[2,1-b][1,3]oxazines was achieved under catalyst-free conditions in water.

Synthesis of new chiral lactam-fused pyridine derivatives

An acid promoted cyclisation of benzylidene-modified tetramic acid and various enamines followed by MnO₂ oxidation afforded the corresponding C₂-symmetric and unsymmetric lactam-fused pyridines in enantiomerically pure forms.

FPR2/ALXR agonists and the resolution of inflammation

The resolution of inflammation (RoI), once believed to be a passive process, has lately been shown to be an active and delicately orchestrated process. During the resolution phase of acute inflammation, novel mediators, including lipoxins and resolvins, which are members of the specialized pro-resolving mediators of inflammation, are produced. FPR2/ALXR, a receptor modulated by some of these lipids as well as by peptides (e.g., annexin A1), has been shown to be one of the receptors involved in the RoI. The aim of this perspective is to present the concept of the RoI from a medicinal chemistry point of view and to highlight the effort of the research community to discover and develop anti-inflammatory/pro-resolution small molecules to orchestrate inflammation by activation of FPR2/ALXR.