Modular synthesis of radicicol A and related resorcylic acid lactones, potent kinase inhibitors

TAK1 inhibition mitigates intracerebral hemorrhage-induced brain injury through reduction of oxidative stress and neuronal pyroptosis via the NRF2 signaling pathway

Introduction

Intracerebral hemorrhage (ICH) often triggers oxidative stress through reactive oxygen species (ROS). Transforming growth factor-β-activated kinase 1 (TAK1) plays a pivotal role in regulating oxidative stress and inflammation across various diseases. 5Z-7-Oxozeaenol (OZ), a specific inhibitor of TAK1, has exhibited therapeutic effects in various conditions. However, the impact of OZ following ICH and its underlying molecular mechanisms remain elusive. This study aimed to explore the possible role of OZ in ICH and its underlying mechanisms by inhibiting oxidative stress-mediated pyroptosis.

Methods

Adult male Sprague-Dawley rats were subjected to an ICH model, followed by treatment with OZ. Neurobehavioral function, blood-brain barrier integrity, neuronal pyroptosis, and oxidative stress markers were assessed using various techniques including behavioral tests, immunofluorescence staining, western blotting, transmission electron microscopy, and biochemical assays.

Results

Our study revealed that OZ administration significantly inhibited phosphorylated TAK1 expression post-ICH. Furthermore, TAK1 blockade by OZ attenuated blood-brain barrier (BBB) disruption, neuroinflammation, and oxidative damage while enhancing neurobehavioral function. Mechanistically, OZ administration markedly reduced ROS production and oxidative stress by facilitating nuclear factor-erythroid 2-related factor 2 (NRF2) nuclear translocation. This was accompanied by a subsequent suppression of the NOD-like receptor protein 3 (NLRP3) activation-mediated inflammatory cascade and neuronal pyroptosis.

Discussion

Our findings highlight that OZ alleviates brain injury and oxidative stress-mediated pyroptosis via the NRF2 pathway. Inhibition of TAK1 emerges as a promising approach for managing ICH.

Takinib inhibits microglial M1 polarization and oxidative damage after subarachnoid hemorrhage by targeting TAK1-dependent NLRP3 inflammasome signaling pathway

Transforming growth factor-β-activated kinase 1 (TAK1) positively regulates oxidative stress and inflammation in different diseases. Takinib, a novel and specific TAK1 inhibitor, has beneficial effects in a variety of disorders. However, the effects of takinib on early brain injury (EBI) after subarachnoid hemorrhage (SAH) and the underlying molecular mechanisms remain unknown. Our study showed that takinib administration significantly inhibited phosphorylated TAK1 expression after SAH. In addition, takinib suppressed M1 microglial polarization and promoted M2 microglial polarization. Furthermore, blockade of TAK1 by takinib reduced neuroinflammation, oxidative damage, brain edema, and neuronal apoptosis, and improved neurological behavior after SAH. Mechanistically, we revealed that TAK1 inhibition by takinib mitigated reactive oxygen species (ROS) production and ROS-mediated nod-like receptor pyrin domain-containing protein 3 (NLRP3) inflammasome activation. In contrast, NLRP3 activation by nigericin abated the neuroprotective effects of takinib against EBI after SAH. In general, our study demonstrated that takinib could protect against EBI by targeting TAK1-ROS-NLRP3 inflammasome signaling. Inhibition of TAK1 might be a promising option in the management of SAH.

TAK1 blockade as a therapy for retinal neovascularization

Retinal neovascularization, or pathological angiogenesis in the retina, is a leading cause of blindness in developed countries. Transforming growth factor-β-activated kinase 1 (TAK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK) activated by TGF-β1 and other proinflammatory cytokines. TAK1 is also a key mediator of proinflammatory signals and plays an important role in maintaining vascular integrity upon proinflammatory cytokine stimulation such as TNFα. However, its role in pathological angiogenesis, particularly in retinal neovascularization, remains unclear. Here, we investigate the regulatory role of TAK1 in human endothelial cells responding to inflammatory stimuli and in a rat model of oxygen-induced retinopathy (OIR) featured retinal neovascularization. Using TAK1 knockout human endothelial cells that subjected to inflammatory stimuli, transcriptome analysis revealed that TAK1 is required for activation of NFκB signaling and mediates its downstream gene expression related to endothelial activation and angiogenesis. Moreover, pharmacological inhibition of TAK1 by 5Z-7-oxozeaenol attenuated angiogenic activities of endothelial cells. Transcriptome analysis also revealed enrichment of TAK1-mediated NFκB signaling pathway in the retina of OIR rats and retinal neovascular membrane from patients with proliferative diabetic retinopathy. Intravitreal injection of 5Z-7-oxozeaenol significantly reduced hypoxia-induced inflammation and microglial activation, thus attenuating aberrant retinal angiogenesis in OIR rats. Our data suggest that inhibition of TAK1 may have therapeutic potential for the treatment of retinal neovascular pathologies.

Natural and Synthetic Lactones Possessing Antitumor Activities

Cancer is one of the leading causes of death globally, accounting for an estimated 8 million deaths each year. As a result, there have been urgent unmet medical needs to discover novel oncology drugs. Natural and synthetic lactones have a broad spectrum of biological uses including anti-tumor, anti-helminthic, anti-microbial, and anti-inflammatory activities. Particularly, several natural and synthetic lactones have emerged as anti-cancer agents over the past decades. In this review, we address natural and synthetic lactones focusing on their anti-tumor activities and synthetic routes. Moreover, we aim to highlight our journey towards chemical modification and biological evaluation of a resorcylic acid lactone, L-783277 (4). We anticipate that utilization of the natural and synthetic lactones as novel scaffolds would benefit the process of oncology drug discovery campaigns based on natural products.

Beta resorcylic acid lactones (RALs) from fungi: chemistry, biology, and biosynthesis

β-Resorcylic acid lactones (RALs) are one of the major polyketides produced by fungi, and some of them have a diverse array of biological activities. Most RALs feature a 14-membered macrocyclic ring fused to β-resorcylic acid (2,4-dihydroxybenzoic acid). In this review, more than 100 RAL-type of compounds are structurally classified into three groups; 14-membered RALs with 17R configuration, 14-membered RALs with 17S configuration, and benzopyranones/benzofuranones, and they are reviewed comprehensively in terms of chemistry, biological activities, and biosynthetic pathways.

Asymmetric total syntheses of naturally occurring α,β-enone-containing RALs, L-783290 and L-783277 through intramolecular base-mediated macrolactonization reaction

Asymmetric total synthesis of two naturally occurring α,β-enone containing RALs, L-783290 and L-783277 is described in this article. An E-selective Horner-Wadsworth-Emmons (HWE) olefination was used as a key reaction to construct the C7'-C8' olefinic unsaturation in L-783290. An enantiopure alkyne addition to the aldehyde followed by Z-selective partial reduction was employed to construct the C7'-C8' olefinic unsaturation in L-783277. Biomimetic lactonization reaction was used to construct the macrolactone core in both the target molecules.

Identification of a Unique Resorcylic Acid Lactone Derivative That Targets Both Lymphangiogenesis and Angiogenesis

We synthesized 11 novel L-783277 derivatives, in which a structure rigidifying phenyl ring is incorporated into the 14-membered chiral resorcylic acid lactone system. The SAR study with these substances demonstrated that 17 possesses excellent kinase selectivity against a panel of 335 kinases in contrast to L-783277 and inhibits VEGFR3, VEGFR2, and FLT3 with single-digit nanomolar IC₅₀ values. Also, we found that 21, a stereoisomer of 17, has excellent potency (IC₅₀ = 9 nM) against VEGFR3 and selectivity over VEGFR2 and FLT3. 17, a potent dual VEGFR3 and VEGFR2 inhibitor, effectively suppresses both lymphangiogenesis and angiogenesis in a 3D-microfluidic tumor lymphangiogenesis assay and in vivo corneal assay while SAR131675 blocks only lymphangiogenesis. In addition, 17 blocks the endothelial tube formation and suppresses proliferation of PHE tumor vascular model. 17 will be a valuable templatefor developing therapeutically active and selective substances that target both lymphangiogenesis and angiogenesis.

Catalytic carboboration of dienylboronate for stereoselective synthesis of (E)-γ′,δ-bisboryl-anti-homoallylic alcohols

A Cu-catalyzed stereoselective carboboration of dienylboronate for the synthesis of (E)-γ′,δ-bisboryl-anti-homoallylic alcohols was developed.

A Concise and Stereoselective Total Synthesis of Paecilomycin E

A concise approach for the first total synthesis of paecilomycin E is described involving Alder-Rickert reaction, Mitsunobu esterification and ring closing metathesis as the key steps. This approach has successfully demonstrated the Alder-Rickert protocol for the construction of resorcylic acid unit.

Resorcylic acid lactones (RALs) and their structural congeners: recent advances in their biosynthesis, chemical synthesis and biology

Resorcylic acid lactones (RALs) are naturally occurring 14-membered macrolactones that constitute a class of polyketides derived from fungal metabolites and that possess significant and promising biological activity.

Synthesis of deoxyelephantopin analogues

Deoxyelephantopin is a sesquiterpene lactone that was reported to be as effective in the treatment of mammary tumours and lung metastasis as taxol based on a murine orthotopic cancer model. Its germacrene skeleton harbours three Michael acceptors that can potentially engage a target covalently. Its strained 10-membered ring is densely functionalised and represents an important synthetic challenge. We herein describe our studies towards deoxyelephantopins using a ring-closing metathesis approach and report some unexpected observations.

An efficient synthesis of an exo-enone analogue of LL-Z1640-2 and evaluation of its protein kinase inhibitory activities

An efficient synthesis of an exo-enone analogue (5) of resorcylic acid lactone (RAL), natural product LL-Z1640-2 (1), has been achieved using a Ni-catalysed regioselective reductive coupling macrocyclisation of an alkyne-aldehyde as a key step. The synthetic route is significantly shorter than those for the natural product and avoids the isomerisation problem of the cis-double bond in the molecule. The preliminary biological evaluation showed that the exo-enone analogue is a potent inhibitor of several important kinases relevant to cancer drug development.

Screening for covalent inhibitors using DNA-display of small molecule libraries functionalized with cysteine reactive moieties

Discriminating between non-covalent and covalent inhibitors with SDS wash in microarray-based screen.

Hyalodendriellins A–F, new 14-membered resorcylic acid lactones from the endophytic fungus Hyalodendriella sp. Ponipodef12

Six new 14-membered resorcylic acid lactones (RALs), named hyalodendriellins A–F (1–6), were isolated from the culture of the endophytic fungus Hyalodendriella sp.

Isolation, semisynthesis, covalent docking and transforming growth factor beta-activated kinase 1 (TAK1)-inhibitory activities of (5Z)-7-oxozeaenol analogues

(5Z)-7-Oxozeanol and related analogues were isolated and screened to explore their activity as TAK1 inhibitors. Seven analogues were synthesized and more than a score of natural products isolated that examined the role that different areas of the molecule contribute to TAK1 inhibition. A novel nonaromatic difluoro-derivative was synthesized that had similar potency compared to the lead. This is the first example of a nonaromatic compound in this class to have TAK1 inhibition. Covalent docking for the isolated and synthesized analogues was carried out and found a strong correlation between the observed activities and the calculated binding.

Modular total syntheses of the marine-derived resorcylic Acid lactones cochliomycins a and B using a late-stage nozaki-hiyama-kishi macrocyclization reaction

The natural products cochliomycin A (1) and cochliomycin B (2), two resorcylic acid lactones obtained from marine sources, have been prepared in a concise and stereocontrolled manner from the readily accessible building blocks 4-6. Olefin cross-metathesis, trans-esterification and Nozaki-Hiyama-Kishi (NHK) macrocyclization reactions were employed in the key steps. Hydrolysis of the immediate precursor to cochliomycin B affords the resorcylic acid lactone zeaenol (24).

Designed Macrocyclic Kinase Inhibitors

Cancer continues to present as an increasing and serious global unmet medical need in today's aging population.1 Macrocyclic kinase inhibitors have reached advanced clinical testing and are making an impact in oncologic conditions including myelofibrosis, lymphomas and leukemias. Rheumatoid arthritis (RA) is also beginning to be impacted with the first macrocycle having entered Phase I clinical evaluation in healthy volunteers. Increasing reports of innovative macrocycles in preclinical research are appearing in the literature. Desirable, selective, multi-kinase inhibitory profiles against specific kinases known to be abrogated in cancer, RA, and other diseases have been achieved in a first generation series of clinical stage compact small molecule macrocyclic kinase inhibitors. Herein we discuss their design, synthesis, structure activity relationships and assessment of the latest clinical data in a range of oncologic conditions. Macrocyclic kinase inhibitors have the potential to offer new hope to patients and their families.

Asymmetric total synthesis of paecilomycin E, 10'-epi-paecilomycin E and 6'-epi-cochliomycin C

The asymmetric total syntheses of naturally occurring resorcylic acid lactone paecilomycin E and two of its structural congeners have been reported in this article. The major highlight of the synthetic venture is the application of the late stage Mitsunobu macrolactonization method (as it is difficult to achieve the desired products through the standard carboxyl activation method) of a properly functionalized seco-acid. The macrolactonization precursor was synthesized by applying an "E"-selective Julia-Kocienski olefination of a highly functionalized aromatic aldehyde and a sulphone, which constitutes all the stereocenters (C4', C5', C6' and C10'; 3S,7R,8R,9S) in the target molecule.

Recent progress regarding the bioactivities, biosynthesis and synthesis of naturally occurring resorcinolic macrolides

Macrolides, which comprise a family of lactones with different ring sizes, belong to the polyketide class of natural products. Resorcinolic macrolides, an important subgroup, possess interesting structures and exhibit a wide variety of bioactivities, such as anti-tumor, anti-bacteria, and anti-malaria activities, etc. This review summarizes progress in isolation, bioactivity studies, biosynthesis, and representative chemical syntheses of this group of macrolides in recent decades, encompassing 63 naturally occurring macrolides published in 120 articles.

Macrocycles in new drug discovery

The use of drug-like macrocycles is emerging as an exciting area of medicinal chemistry, with several recent examples highlighting the favorable changes in biological and physicochemical properties that macrocyclization can afford. Natural product macrocycles and their synthetic derivatives have long been clinically useful and attention is now being focused on the wider use of macrocyclic scaffolds in medicinal chemistry in the search for new drugs for increasingly challenging targets. With the increasing awareness of concepts of drug-likeness and the dangers of ‘molecular obesity’, functionalized macrocyclic scaffolds could provide a way to generate ligand-efficient molecules with enhanced properties. In this review we will separately discuss the effects of macrocyclization upon potency, selectivity and physicochemical properties, concentrating on recent case histories in oncology drug discovery. Additionally, we will highlight selected advances in the synthesis of macrocycles and provide an outlook on the future use of macrocyclic scaffolds in medicinal chemistry.

Polyubiquitination of transforming growth factor β (TGFβ)-associated kinase 1 mediates nuclear factor-κB activation in response to different inflammatory stimuli

The transcription factor nuclear factor κB (NF-κB) plays a central role in regulating inflammation in response to several external signals. The TGFβ-associated kinase 1 (TAK1) is an upstream regulator of NF-κB signaling. In TGFβ-stimulated cells, TAK1 undergoes Lys-63-linked polyubiquitination at Lys-34 by TNF receptor-associated factor 6 and is thereby activated. The aim of this study was to investigate whether TAK1 polyubiquitination at Lys-34 is also essential for NF-κB activation via TNF receptor, IL-1 receptor and toll-like receptor 4. We observed that TAK1 polyubiquitination occurred at Lys-34 and required the E3 ubiquitin ligase TNF receptor-associated factor 6 after stimulation of cells with IL-1β. Polyubiquitination of TAK1 also occurred at Lys-34 in cells stimulated by TNF-α and LPS, which activates TLR4, as well as in HepG2 and prostate cancer cells stimulated with TGFβ, which in all cases resulted in NF-κB activation. Expression of a K34R-mutant TAK1 led to a reduced NF-κB activation, IL-6 promoter activity, and proinflammatory cytokine secretion by TNF-α-stimulated PC-3U cells. Similar results were obtained in the mouse macrophage cell line RAW264.7 after LPS treatment. In conclusion, polyubiquitination of TAK1 is correlated with activation of TAK1 and is essential for activation of NF-κB signaling downstream of several receptors.

Cysteine mapping in conformationally distinct kinase nucleotide binding sites: application to the design of selective covalent inhibitors

Kinases have emerged as one of the most prolific therapeutic targets. An important criterion in the therapeutic success of inhibitors targeting the nucleotide binding pocket of kinases is the inhibitor residence time. Recently, covalent kinase inhibitors have attracted attention since they confer terminal inhibition and should thus be more effective than reversible inhibitors with transient inhibition. The most robust approach to design irreversible inhibitors is to capitalize on the nucleophilicity of a cysteine thiol group present in the target protein. Herein, we report a systematic analysis of cysteine residues present in the nucleotide binding site of kinases, which could be harnessed for irreversible inhibition, taking into consideration the different kinase conformations. We demonstrate the predictive power of this analysis with the design and validation of an irreversible inhibitor of KIT/PDGFR kinases. This is the first example of a covalent kinase inhibitor that combines a pharmacophore addressing the DFG-out conformation with a covalent trap.

Total synthesis of LL-Z1640-2 utilizing a late-stage intramolecular Nozaki-Hiyama-Kishi reaction

A total synthesis of LL-Z1640-2 (2), a potent and selective kinase inhibitor, has been completed. The key step of the convergent synthesis utilized a late-stage intramolecular Nozaki-Hiyama-Kishi (NHK) reaction to close the macrocycle at the C6'-C7' bond.

Total synthesis of TAK-kinase inhibitor LL-Z1640-2 via consecutive macrocyclization and transannular aromatization

The biomimetic total synthesis of LL-Z1640-2 (3) is reported without the use of phenol protection. The aromatic unit was constructed via the transannular aromatization of macrocyclic triketo-ester 2, which in turn was synthesized by macrolactonization using an intramolecular trapping of a triketo-ketene derived from dioxinone 1.

Insights into radicicol biosynthesis via heterologous synthesis of intermediates and analogs

Resorcylic acid lactones are fungal polyketides that display diverse biological activities, with the potent Hsp90 inhibitor radicicol being an important representative member. Two fungal iterative polyketide synthases (IPKSs), Rdc5, the highly reducing IPKS, and Rdc1, the nonreducing IPKS, are required for the biosynthesis of radicicol in Pochonia chlamydosporia. In this study, the complete reconstitution of Rdc5 and Rdc1 activities both in vitro and in Saccharomyces cerevisiae uncovered the earliest resorcylic acid lactone intermediate of the radicicol biosynthetic pathway, (R)-monocillin II. The enzymatic synthesis of (R)-monocillin II confirmed the exquisite timing of the Rdc5 enoyl reductase domain. Using precursor-directed biosynthesis, the chemical modularity of the dual IPKS system was determined. Rdc1 readily accepted an N-acetylcysteamine thioester mimic of the reduced pentaketide product of Rdc5 to synthesize (R)-monocillin II with four additional iterations of polyketide elongation, indicating the C2' ketone group found in (R)-monocillin II is incorporated via the functions of Rdc1 instead of Rdc5. The involvement of the thioesterase domain in Rdc1 in macrolactonization was confirmed through both site-directed mutagenesis and domain deletion. The Rdc1 thioesterase domain was also shown to be tolerant of the opposite stereochemistry of the terminal hydroxyl nucleophile, demonstrated in the precursor-directed synthesis of the enantiomeric (S)-monocillin II. Finally, reconstitution of the halogenase Rdc2 was demonstrated both in vivo and in vitro in the synthesis of pochonin D and a new halogenated analog 6-chloro, 7',8'-dehydrozearalenol.

Autoactivation of transforming growth factor beta-activated kinase 1 is a sequential bimolecular process

Transforming growth factor-beta-activated kinase 1 (TAK1), an MAP3K, is a key player in processing a multitude of inflammatory stimuli. TAK1 autoactivation involves the interplay with TAK1-binding proteins (TAB), e.g. TAB1 and TAB2, and phosphorylation of several activation segment residues. However, the TAK1 autoactivation is not yet fully understood on the molecular level due to the static nature of available x-ray structural data and the complexity of cellular systems applied for investigation. Here, we established a bacterial expression system to generate recombinant mammalian TAK1 complexes. Co-expression of TAK1 and TAB1, but not TAB2, resulted in a functional and active TAK1-TAB1 complex capable of directly activating full-length heterotrimeric mammalian AMP-activated protein kinase (AMPK) in vitro. TAK1-dependent AMPK activation was mediated via hydrophobic residues of the AMPK kinase domain alphaG-helix as observed in vitro and in transfected cell culture. Co-immunoprecipitation of differently epitope-tagged TAK1 from transfected cells and mutation of hydrophobic alphaG-helix residues in TAK1 point to an intermolecular mechanism of TAB1-induced TAK1 autoactivation, as TAK1 autophosphorylation of the activation segment was impaired in these mutants. TAB1 phosphorylation was enhanced in a subset of these mutants, indicating a critical role of alphaG-helix residues in this process. Analyses of phosphorylation site mutants of the activation segment indicate that autophosphorylation of Ser-192 precedes TAB1 phosphorylation and is followed by sequential phosphorylation of Thr-178, Thr-187, and finally Thr-184. Finally, we present a model for the chronological order of events governing TAB1-induced TAK1 autoactivation.

Inhibition of HSP90 with pochoximes: SAR and structure-based insights

The pochoximes, based on the radicicol pharmacophore, are potent inhibitors of heat shock protein 90 (HSP90) that retain their activity in vivo. Herein we report an extended library that broadly explores the structure-activity relationship (SAR) of the pochoximes with four points of diversity. Several modifications were identified that afford improved cellular efficacy, new opportunities for conjugation, and further diversifications. Cocrystal structures of pochoximes A and B with HSP90 show that pochoximes bind to a different conformation of HSP90 than radicicol and provide a rationale for the enhanced affinity of the pochoximes relative to radicicol and the pochonins.

Divergent syntheses of resorcylic acid lactones: L-783277, LL-Z1640-2, and hypothemycin

The resorcylic acid lactones (RAL) are endowed with diverse biological activity ranging from transcription factor modulators (zearalenone and zearalenol) to HSP90 inhibitors (radicicol and pochonin D) and reversible (aigialomycin D) as well as irreversible kinase inhibitors (hypothemycin and other RAL containing a cis-enone). Our interest in broadening the diversity of this family beyond naturally occurring diversity has led us to seek a general approach that could be used to address the entire spectrum of functionalities present within this family. Herein, we present our efforts on accessing macrocycles bearing an alkane, alkene, or epoxide at the benzylic position from a common benzylic sulfide intermediate to access L-783277, LL-Z1640-2, and hypothemycin.

Synthesis of a resorcylic acid lactone (RAL) library using fluorous-mixture synthesis and profile of its selectivity against a panel of kinases

A library of resorcylic acid lactones (RAL) containing a cis-enone moiety targeting kinases bearing a cysteine residue within the ATP-binding pocket was prepared using a fluorous-mixture synthesis and evaluated against a panel of 19 kinases thus providing important structure-activity trends. Two new analogues were then profiled for their selectivity against a panel of 402 kinases providing the broadest evaluation of this pharmacophores' selectivity.