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Fourier-transform microwave spectroscopy has been applied for the 13C/18O-substituted tropolone to observe tunneling-rotation transitions as well as pure rotational transitions. The tunneling-rotation transitions were observed between the 13C-4 and -6 forms as well as between 13C-3 and -7, between 13C-1 and -2, and between 18O-8 and -9 (we denote these tunneling pairs as 13C-46, etc., below) although they have an asymmetric tunneling potential due to the difference in the zero point energy (ZPE). From the observed tunneling splittings ΔEij (0.9800–1.6824 cm−1), the differences in ZPE Δij for the 13C-46, -37, -12, and 18O-89 species are derived to be −0.1104, 0.5652, −1.3682, and 1.3897 cm−1 to agree well with the DFT calculation. The state mixing ratio of the tunneling states decreases drastically from (44%:56%) to (8.7%:91.3%) for 13C-46 and 18O-89 with an increase in the asymmetry Δij of the tunneling potential function. The observed tunneling-rotation interaction constants Fij decrease from 16.001 to 9.224 cm−1 as the differences in ZPE Δij increase, while the diagonal tunneling-rotation interaction constants Fu increase from 1.767 to 13.70 cm−1, explained well by the mixing ratio of the tunneling states. [ABSTRACT FROM AUTHOR]

A rapid, selective, and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantitation of MO-OH-Nap tropolone (MO-OH-Nap) in mouse plasma. MO-OH-Nap is an α-substituted tropolone with anti-proliferative properties in various cancer cell lines. Detection and separation of analytes was achieved on an ACE Excel C18 (1.7 µm, 100 × 2.1 mm, MAC-MOD Analytical, Chadds Ford, PA, USA) column with mobile phase consisting of 0.05% trifluoroacetic acid in water (mobile phase A) and 0.05% trifluoroacetic acid in acetonitrile (mobile phase B), with an isocratic elution of 15:85% (A:B) at a total flow rate of 0.25 mL/min. The LC-MS/MS system was operated at unit resolution in multiple reaction monitoring (MRM) mode, using precursor ion > product ion combination of 249.10 > 202.15 m/z for MO-OH-Nap and 305.10 > 215.05 m/z for the internal standard (IS), BA-SM-OM. The MS/MS response was linear over a concentration range of 1 to 500 ng/mL with a correlation coefficient (r2) of ≥0.987. The within- and between-batch precision (%RSD) and accuracy (%Bias) were within acceptable limits. The validated method was successfully applied to determine MO-OH-Nap metabolic stability, plasma protein binding, and bio-distribution studies of MO-OH-Nap in CD-1 mice. [ABSTRACT FROM AUTHOR]

Abstract Background Isatropolone A and C, produced by Streptomyces sp. CPCC 204095, belong to an unusual class of non-benzenoid aromatic compounds and contain a rare seven-membered ring structure. Isatropolone A exhibits potent activity against Leishmania donovani, comparable to the only oral drug miltefosine. However, its variably low productivity represents a limitation for this lead compound in the future development of new anti-leishmaniasis drugs to meet unmet clinical needs. Results Here we first elucidated the regulatory cascade of biosynthesis of isatropolones, which consists of two SARP family regulators, IsaF and IsaJ. Through a series of in vivo and in vitro experiments, IsaF was identified as a pathway-specific activator that orchestrates the transcription of the gene cluster essential for isatropolone biosynthesis. Interestingly, IsaJ was found to only upregulate the expression of the cytochrome P450 monooxygenase IsaS, which is crucial for the yield and proportion of isatropolone A and C. Through targeted gene deletions of isaJ or isaS, we effectively impeded the conversion of isatropolone A to C. Concurrently, the facilitation of isaF overexpression governed by selected promoters, prompted the comprehensive activation of the production of isatropolone A. Furthermore, meticulous optimization of the fermentation parameters was conducted. These strategies culminated in the attainment of an unprecedented maximum yield—980.8 mg/L of isatropolone A—achieved in small-scale solid-state fermentation utilizing the genetically modified strains, thereby establishing the highest reported titer to date. Conclusion In Streptomyces sp. CPCC 204095, the production of isatropolone A and C is modulated by the SARP regulators IsaF and IsaJ. IsaF serves as a master pathway-specific regulator for the production of isatropolones. IsaJ, on the other hand, only dictates the transcription of IsaS, the enzyme responsible for the conversion of isatropolone A and C. By engineering the expression of these pivotal genes, we have devised a strategy for genetic modification aimed at the selective and high-yield biosynthesis of isatropolone A. This study not only unveils the unique regulatory mechanisms governing isatropolone biosynthesis for the first time, but also establishes an essential engineering framework for the targeted high-level production of isatropolone A.

Background: Isatropolone A and C, produced by Streptomyces sp. CPCC 204095, belong to an unusual class of non-benzenoid aromatic compounds and contain a rare seven-membered ring structure. Isatropolone A exhibits potent activity against Leishmania donovani, comparable to the only oral drug miltefosine. However, its variably low productivity represents a limitation for this lead compound in the future development of new anti-leishmaniasis drugs to meet unmet clinical needs. Results: Here we first elucidated the regulatory cascade of biosynthesis of isatropolones, which consists of two SARP family regulators, IsaF and IsaJ. Through a series of in vivo and in vitro experiments, IsaF was identified as a pathway-specific activator that orchestrates the transcription of the gene cluster essential for isatropolone biosynthesis. Interestingly, IsaJ was found to only upregulate the expression of the cytochrome P450 monooxygenase IsaS, which is crucial for the yield and proportion of isatropolone A and C. Through targeted gene deletions of isaJ or isaS, we effectively impeded the conversion of isatropolone A to C. Concurrently, the facilitation of isaF overexpression governed by selected promoters, prompted the comprehensive activation of the production of isatropolone A. Furthermore, meticulous optimization of the fermentation parameters was conducted. These strategies culminated in the attainment of an unprecedented maximum yield—980.8 mg/L of isatropolone A—achieved in small-scale solid-state fermentation utilizing the genetically modified strains, thereby establishing the highest reported titer to date. Conclusion: In Streptomyces sp. CPCC 204095, the production of isatropolone A and C is modulated by the SARP regulators IsaF and IsaJ. IsaF serves as a master pathway-specific regulator for the production of isatropolones. IsaJ, on the other hand, only dictates the transcription of IsaS, the enzyme responsible for the conversion of isatropolone A and C. By engineering the expression of these pivotal genes, we have devised a strategy for genetic modification aimed at the selective and high-yield biosynthesis of isatropolone A. This study not only unveils the unique regulatory mechanisms governing isatropolone biosynthesis for the first time, but also establishes an essential engineering framework for the targeted high-level production of isatropolone A. [ABSTRACT FROM AUTHOR]

This article presents the synthesis and characterization of a fluorescent nucleoside analogue called tropolonyl triazolyl-dU (tt-dU). The tt-dU analogue demonstrates solvatochromism, meaning its absorption and emission properties change depending on the solvent used. The authors synthesized tt-dU using a copper(I)-catalyzed click chemistry reaction and evaluated its photophysical properties in different solvents. This research contributes to the development of fluorescent nucleic acids for studying biochemical processes and monitoring cellular phenomena. The article also discusses the potential applications of tt-dU as a fluorescent nucleoside analogue for designing DNA-based fluorescence probes. [Extracted from the article]

Osteosarcoma (OS) is a primary malignant bone tumor characterized by frequent metastasis, rapid disease progression, and a high rate of mortality. Treatment options for OS have remained largely unchanged for decades, consisting primarily of cytotoxic chemotherapy and surgery, thus necessitating the urgent need for novel therapies. Tropolones are naturally occurring seven‐membered non‐benzenoid aromatic compounds that possess antiproliferative effects in a wide array of cancer cell types. MO‐OH‐Nap is an α‐substituted tropolone that has activity as an iron chelator. Here, we demonstrate that MO‐OH‐Nap activates all three arms of the unfolded protein response (UPR) pathway and induces apoptosis in a panel of human OS cell lines. Co‐incubation with ferric chloride or ammonium ferrous sulfate completely prevents the induction of apoptotic and UPR markers in MO‐OH‐Nap‐treated OS cells. MO‐OH‐Nap upregulates transferrin receptor 1 (TFR1) protein levels, as well as TFR1, divalent metal transporter 1 (DMT1), iron‐regulatory proteins (IRP1, IRP2), ferroportin (FPN), and zinc transporter 14 (ZIP14) transcript levels, demonstrating the impact of MO‐OH‐Nap on iron‐homeostasis pathways in OS cells. Furthermore, MO‐OH‐Nap treatment restricts the migration and invasion of OS cells in vitro. Lastly, metabolomic profiling of MO‐OH‐Nap‐treated OS cells revealed distinct changes in purine and pyrimidine metabolism. Collectively, we demonstrate that MO‐OH‐Nap‐induced cytotoxic effects in OS cells are dependent on the tropolone's ability to alter cellular iron availability and that this agent exploits key metabolic pathways. These studies support further evaluation of MO‐OH‐Nap as a novel treatment for OS. [ABSTRACT FROM AUTHOR]

New troponoid liquid crystals with 5-(4-alkoxyphenylethynyl)tropolone cores were synthesized. The 5-(4-alkoxyphenylethynyl)tropolones were obtained by the palladium-catalyzed cross-coupling of 5-iodotropolone with 4-alkoxyphenylacetylenes. The 2-alkoxy-5-(4-alkoxyphenylethynyl)tropones (1A) showed enantiotropic smectic phases, such as smectic A, C, and B. The 2-(4-alkoxy)benzoyloxy-5-(4-alkoxyphenylethynyl)tropones (1B) had enantiotropic nematic and smectic C phases. The 2-alkoxytropone derivatives (1A) had higher clearing temperatures and lower melting points than the corresponding benzene derivatives (2A). However, the 2-(4-alkoxybenzoyl)tropone derivatives (1B) had lower clearing temperatures and higher melting points than the corresponding benzene derivatives (2B). [ABSTRACT FROM AUTHOR]

A rapid, selective, and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantitation of MO-OH-Nap tropolone (MO-OH-Nap) in mouse plasma. MO-OH-Nap is an α-substituted tropolone with anti-proliferative properties in various cancer cell lines. Detection and separation of analytes was achieved on an ACE Excel C18 (1.7 µm, 100 × 2.1 mm, MAC-MOD Analytical, Chadds Ford, PA, USA) column with mobile phase consisting of 0.05% trifluoroacetic acid in water (mobile phase A) and 0.05% trifluoroacetic acid in acetonitrile (mobile phase B), with an isocratic elution of 15:85% (A:B) at a total flow rate of 0.25 mL/min. The LC-MS/MS system was operated at unit resolution in multiple reaction monitoring (MRM) mode, using precursor ion > product ion combination of 249.10 > 202.15 m/z for MO-OH-Nap and 305.10 > 215.05 m/z for the internal standard (IS), BA-SM-OM. The MS/MS response was linear over a concentration range of 1 to 500 ng/mL with a correlation coefficient (r2) of ≥0.987. The within- and between-batch precision (%RSD) and accuracy (%Bias) were within acceptable limits. The validated method was successfully applied to determine MO-OH-Nap metabolic stability, plasma protein binding, and bio-distribution studies of MO-OH-Nap in CD-1 mice.

While metal-based complexes are deeply investigated as anticancer chemotherapeutic drugs, fewer studies are devoted to their anti-invasive activity. Herein, two copper (Cu)(II) tropolone derivatives, [Cu(Trop)Cl] and [Cu(Trop)Sac], both containing the N,N-chelated 4,4′-bishydroxymethyl-2,2′-bipyridne ligand, were evaluated for their anticancer and anti-invasive properties. RKO (RKO-ctr) colon cancer cells and their derivatives undergoing stable small interference (si) RNA for HIPK2 protein (RKO-siHIPK2) with acquisition of pro-invasive capacity were used. The results demonstrate that while [Cu(Trop)Sac] did not show cytotoxic activity, [Cu(Trop)Cl] induced cell death in both RKO-ctr and RKO-siHIPK2 cells, indicating that structural changes on substituting the coordinated chloride ligand with saccharine (Sac) could be a key factor in suppressing mechanisms of cellular death. On the other hand, both [Cu(Trop)Sac] and [Cu(Trop)Cl] complexes counteracted RKO-siHIPK2 cell migration in the wound healing assay. The synergic effect exerted by the concomitant presence of both tropolone and saccharin ligands in [Cu(Trop)Sac] was also supported by its significant inhibition of RKO-siHIPK2 cell migration compared to the free Sac ligand. These data suggest that the two Cu(II) tropolone derivatives are also interesting candidates to be further tested in in vivo models as an anti-invasive tumor strategy. [ABSTRACT FROM AUTHOR]

The sesquiterpene-tropolones belong to a distinctive structural class of meroterpene natural products with impressive biological activities, including anticancer, antifungal, antimalarial, and antibacterial. In this article, we describe a concise, modular, and cycloaddition-based approach to a series of sesquiterpene mono- and bistropolones, including (-)-epolone B, (+)-isoepolone B, (±)-dehydroxypycnidione, and (-)-10-epi-pycnidione. Alongside the development of a general strategy to access this unique family of metabolites were computational modeling studies that justified the diastereoselectivity observed during key cycloadditions. Ultimately, these studies prompted stereochemical reassignments of the pycnidione subclass and shed additional light on the biosynthesis of these remarkable natural products.

Internal conversion decay dynamics associated with the potential energy surfaces of three low-lying singlet excited electronic states, S1 (ππ*, A′), S2 (ππ*, A′), and S3 (nπ*, A″), of tropolone are investigated theoretically. Energetic and spatial aspects of conical intersections of these electronic states are explored with the aid of the linear vibronic coupling approach. Symmetry selection rules suggest that non-totally symmetric modes would act as coupling modes between S1 and S3 as well as between S2 and S3. We found that the S1–S2 interstate coupling via totally symmetric modes is very weak. A diabatic vibronic Hamiltonian consisting of 32 vibrational degrees of freedom is constructed to simulate the photoinduced dynamics of S0 → S1 and S0 → S2 transitions. We observe a direct nonadiabatic population transfer from S1 to S3, bypassing S2, during the initial wavepacket propagation on S1. On the other hand, the initial wavepacket evolving on S2 would pass through the S2–S3 and S1–S3 conical intersections before reaching S1. The presence of multiple proton transfer channels on the S1–S2–S3 coupled potential energy surfaces of tropolone is analyzed. Our findings necessitate the treatment of proton tunneling dynamics of tropolone beyond the adiabatic symmetric double well potentials. [ABSTRACT FROM AUTHOR]

A bacterial strain, Pseudomonas bohemica strain ins3 was newly isolated as a resistant strain against high concentrations of hinokitiol. This strain was revealed not only to show resistance but also completely remove this compound from its culture broth. In addition, its mechanism was revealed to be independent of conventional aromatic dioxygenases, ie catechol-1,2- or 2,3-dioxygenases. [ABSTRACT FROM AUTHOR]

The nucleobase modified fluorescent DNA and RNA analogs are synthesized by the conjugation of aromatic scaffolds through linkers, comprising mostly ethyne/ethene or fused ring residues at the pyrimidine/purine ring. These scaffolds are mainly derived from the benzenoid aromatic molecules comprising electron withdrawing/donating characters. However, non-benzenoid aromatic scaffolds such as tropolone and related derivatives are constituents of various troponoid natural products. The conjugation of nucleobases with a troponyl moiety is underutilized for the synthesis of fluorescent DNA analogs. This report describes the synthesis and photophysical studies of 2-aminotroponyl conjugated deoxyuridine nucleosides and their DNA analogs. 2-Aminotropone derivatives are conjugated at the C-5 position of uridine through an ethynyl linker/pyrrolyl ring fusion and their DNA analogs. Their photophysical studies reveal that aminotroponyl deoxyuridine analogs exhibit solvent-dependent fluorescence properties. Moreover, pyrrolyl ring-fused aminotroponyl DNA oligonucleotides enhance the fluorescence after formation of duplexation with complementary sequences of native DNA oligonucleotides. Hence, these modified nucleosides and DNA are promising fluorescent analogs which could be useful to design the sequence-specific DNA probes. [ABSTRACT FROM AUTHOR]

While metal-based complexes are deeply investigated as anticancer chemotherapeutic drugs, fewer studies are devoted to their anti-invasive activity. Herein, two copper (Cu)(II) tropolone derivatives, [Cu(Trop)Cl] and [Cu(Trop)Sac], both containing the N,N-chelated 4,4′-bishydroxymethyl-2,2′-bipyridne ligand, were evaluated for their anticancer and anti-invasive properties. RKO (RKO-ctr) colon cancer cells and their derivatives undergoing stable small interference (si) RNA for HIPK2 protein (RKO-siHIPK2) with acquisition of pro-invasive capacity were used. The results demonstrate that while [Cu(Trop)Sac] did not show cytotoxic activity, [Cu(Trop)Cl] induced cell death in both RKO-ctr and RKO-siHIPK2 cells, indicating that structural changes on substituting the coordinated chloride ligand with saccharine (Sac) could be a key factor in suppressing mechanisms of cellular death. On the other hand, both [Cu(Trop)Sac] and [Cu(Trop)Cl] complexes counteracted RKO-siHIPK2 cell migration in the wound healing assay. The synergic effect exerted by the concomitant presence of both tropolone and saccharin ligands in [Cu(Trop)Sac] was also supported by its significant inhibition of RKO-siHIPK2 cell migration compared to the free Sac ligand. These data suggest that the two Cu(II) tropolone derivatives are also interesting candidates to be further tested in in vivo models as an anti-invasive tumor strategy.

The influence of base type, temperature, and solvent on regioselective C(9)/C(10) "click" modifications within the tropolone ring of colchiceine (2) is investigated. New ether derivatives of 2, bearing alkyne, azide, vinyl, or halide aryl groups enable assembly of the alkaloid part with heterocycles or important bio-molecules such as saccharides, geldanamycin or AZT into hybrid scaffolds by dipolar cycloaddition (CuAAC) or Heck reaction. Compared to colchicine (1) or colchiceine (2), ether congeners, as e.g. 3e [IC50s(3e) ~ 0.9 nM], show improved or similar anticancer effects, whereby the bulkiness of the substituents and the substitution pattern of the tropolone proved to be essential. Biological studies reveal that expanding the ether arms by terminal basic heterocycles as quinoline or pyridine, decreases the toxicity in HDF cells at high anticancer potency (IC50s ~ 1-2 nM). Docking of ether and hybrid derivatives into the colchicine pocket of αGTP/β tubulin dimers reveals a relationship between the favourable binding mode and the attractive anticancer potency. [ABSTRACT FROM AUTHOR]

The scarcity of novel bioactive molecules against multidrug‐resistant (MDR) bacterial strains like Pseudomonas aeruginosa is alarming. This bacterial virulence is regulated via Quorum sensing (QS), a cell‐cell communication process. Disabling QS circuits (las, pqs, rhl) with small molecules has been proposed as a potential strategy to prevent bacterial pathogenicity. This strategy focuses on interruption of bacterial virulence, rather than killing them to tackle the drug resistance problem. Herein, we describe the synthesis of rationally designed Alklyamionotroponyl Sulfone (ATS) derivatives by Cu‐catalyzed C(sp2)−H functionalization at tropone ring and the screening of their anti‐QS activity against P. aeruginosa. Importantly, two sulfones (∼20 μM) remarkably exhibit the down regulation of the lasI/R QS genes. These molecules also inhibit swarming motility, biofilm formation and pyocyanin production, which reduce P. aeruginosa virulence in cells. Hence, ATS derivatives could be considered as potential therapeutic candidates for the treatment of P. aeruginosa infections. [ABSTRACT FROM AUTHOR]

This review summarises the known structures, biological activities, and biosynthetic pathways of the tropolone sesquiterpenoid family of fungal secondary metabolites. Synthesis of this knowledge allows likely structural and stereochemical misassignments to be revised and shows how the compounds can be divided into three main biosynthetic classes based on the stereochemistry of key biosynthetic steps. [ABSTRACT FROM AUTHOR]

Phytochelators have been studied as templates for designing new drugs for chelation therapy. This work evaluated key chemical and biological properties of five candidate phytochelators for iron overload diseases: maltol, mimosine, morin, tropolone, and esculetin. Intra- and extracellular iron affinity and antioxidant activity, as well as the ability to scavenge iron from holo-transferrin, were studied in physiologically relevant settings. Tropolone and mimosine (and, to a lesser extent, maltol) presented good binding capacity for iron, removing it from calcein, a high-affinity fluorescent probe. Tropolone and mimosine arrested iron-mediated oxidation of ascorbate with the same efficiency as the standard iron chelator DFO. Also, both were cell permeant and able to access labile pools of iron in HeLa and HepG2 cells. Mimosine was an effective antioxidant in cells stressed by iron and peroxide, being as efficient as the cell-permeant iron chelator deferiprone. These results reinforce the potential of those molecules, especially mimosine, as adjuvants in treatments for iron overload. [ABSTRACT FROM AUTHOR]

Botrytis cinerea is one of the most devastating pathogen responsible for postharvest decay of fresh fruits and vegetables. However, traditional fungicide application is inclined to develop resistance strains, complicating the control of gray mold. Hence, there is an urgent need for exploiting new antifungal active substances and enhancing their antifungal activity in an environmentally friendly manner. In this study, tropolone was demonstrated efficacy in inhibiting B. cinerea mycelial growth at relatively low (40 mg L−1) tropolone concentrations and spore germination at even lower (10 mg L−1) tropolone concentrations. The antifungal mechanisms were linked to the disruption of spore germination-related gene expression rather than directly killing B. cinerea through cell membrane disruption. The inhibition of spore germination hindered the penetration of B. cinerea into host cells, thereby reducing disease severity in harvested apples and strawberries. To increase the protective effect of tropolone, we prepared small-sized maize starch nanoparticles loaded with tropolone and confirmed an enhanced antifungal effect. This study provides a theoretical foundation for the application of small-sized maize starch nanoparticles to increase antifungal effect and reduce fungicide application in postharvest disease control. • Tropolone suppressed spore germination of Botrytis cinerea. • Tropolone modulated the MAPK cascade and the cAMP-dependent signaling pathway. • Tropolone mitigated the incidence and severity of gray mold in fruit. • Maize starch nanoparticles (MS-NPs) enhanced the antifungal activity of tropolone. [ABSTRACT FROM AUTHOR]

Investigation of natural products is an attractive strategy to identify novel compounds for cancer prevention and treatment. Numerous studies have shown the efficacy and safety of natural products, and they have been widely used as alternative treatments for a wide range of illnesses, including cancers. However, it remains unknown whether natural products affect homologous recombination (HR)-mediated DNA repair and whether these compounds can be used as sensitizers with minimal toxicity to improve patients' responses to radiation therapy, a mainstay of treatment for many human cancers. In this study, in order to systematically identify natural products with an inhibitory effect on HR repair, we developed a high-throughput image-based HR repair screening assay and screened a chemical library containing natural products. Among the most interesting of the candidate compounds identified from the screen was β-thujaplicin, a bioactive compound isolated from the heart wood of plants in the Cupressaceae family, can significantly inhibit HR repair. We further demonstrated that β-thujaplicin inhibits HR repair by reducing the recruitment of a key HR repair protein, Rad51, to DNA double-strand breaks. More importantly, our results showed that β-thujaplicin can radiosensitize cancer cells. Additionally, β-thujaplicin sensitizes cancer cells to PARP inhibitor in different cancer cell lines. Collectively, our findings for the first time identify natural compound β-thujaplicin, which has a good biosafety profile, as a novel HR repair inhibitor with great potential to be translated into clinical applications as a sensitizer to DNA-damage-inducing treatment such as radiation and PARP inhibitor. In addition, our study provides proof of the principle that our robust high-throughput functional HR repair assay can be used for a large-scale screening system to identify novel natural products that regulate DNA repair and cellular responses to DNA damage-inducing treatments such as radiation therapy.

The inhibition and binding of three metal-binding pharmacophores (MBPs), 2-hydroxycyclohepta-2,4,6-trien-1-one (tropolone), 2-mercaptopyridine-N-oxide (1,2-HOPTO), and 2-hydroxycyclohepta-2,4,6-triene-1-thione (thiotropolone) to human carbonic anhydrase II (hCAII) and a mutant protein hCAII L198G were investigated. These MBPs displayed bidentate coordination to the active site Zn(II) metal ion, but the MBPs respond to the mutation of L198G differently, as characterized by inhibition activity assays and X-ray crystallography. The L198G mutation increases the active site volume thereby decreasing the steric pressure exerted on MBPs upon binding, allowing changes in MBP coordination to be observed. When comparing the binding mode of tropolone to thiotropolone or 1,2-HOPTO (O,O versus O,S donor sets), structural modifications of the hCAII active site were shown to have a stronger effect on MBPs with an O,O versus O,S donor set. These findings were corroborated with density functional theory (DFT) calculations of model coordination complexes. These results suggest that the MBP binding geometry is a malleable interaction, particularly for certain ligands, and that the identity of the donor atoms influences the response of the ligand to changes in the protein active site environment. Understanding underlying interactions between a MBP and a metalloenzyme active site may aid in the design and development of potent metalloenzyme inhibitors.

[Display omitted] • Analogues of the fungal metabolite, eupenifeldin, were generated via semisynthesis. • 29 analogues were generated via 22 separate reactions, including esters, carbonates, sulfonates, and carbamates. • Ten analogues maintained nanomolar potency in cytotoxicity assays. • The succinate analogue increased aqueous solubility over 50 times relative to eupenifeldin. Eupenifeldin (1) is a fungal secondary metabolite possessing bis -tropolone moieties that demonstrates nanomolar cytotoxic activity against a number of cancer cell types. As a potential anticancer lead, this meroterpenoid was used to access 29 semisynthetic analogues via functionalization of the reactive hydroxy groups of the bis -tropolones. A series of ester (2 – 6), carbonate (7 – 8), sulfonate (9 – 16), carbamate (17 – 20), and ether (21 – 30) analogues of 1 were generated via 22 reactions. Most of these compounds were disubstituted, produced via functionalization of both of the tropolonic hydroxy moieties, although three mono-functionalized analogues (6 , 8 , and 24) and one tri-functionalized analogue (3) were also obtained. The cytotoxic activities of 1 – 30 were evaluated against human melanoma and ovarian cancer cell lines (i.e., MDA-MB-435 and OVCAR3, respectively). Ester and carbonate analogues of 1 (i.e., 2 – 8) maintained cytotoxicity at the nanomolar level, and the greatest improvement in aqueous solubility came from the monosuccinate analogue (6), which was acylated on the secondary hydroxy at the 11 position. [ABSTRACT FROM AUTHOR]

Two rhenium complexes, namely, fac‐tricarbonyl(triphenylphosphane‐κP)(tropolonato‐κ2O,O′)rhenium(I), [Re(C7H5O2)(C18H15P)(CO)3] or fac‐[Re(Trop)(PPh3)(CO)3] (1), and fac‐tricarbonyl(3,5,7‐tribromotropolonato‐κ2O,O′)(triphenylphosphane‐κP)rhenium(I), [Re(C7H2Br3O2)(C18H15P)(CO)3] or fac‐[Re(TropBr3)(PPh3)(CO)3] (2) (TropH is tropolone and and TropBr3H is tribromotropolone), were synthesized and their crystal and molecular structures confirmed by single‐crystal X‐ray diffraction. Both crystallized in the space group P and display an array of inter‐ and intramolecular interactions which were confirmed by solid‐state 13C NMR spectroscopy using cross polarization magic angle spinning (CPMAS) techniques, as well as Hirshfeld surface analysis. The slightly longer Re—P distance of 1 [2.4987 (5) versus 2.4799 (11) Å for 1 and 2, respectively] suggests stronger back donation from the carbonyl groups in the former case, possibly due to the stronger electron‐donating ability of the unsubstituted tropolonate ring system. However, this is not supported in the Re—CO bond distances of 1 and 2. [ABSTRACT FROM AUTHOR]

Flavin‐dependent enzymes enable a broad range of redox transformations and generally act as monofunctional and stereoselective catalysts. Herein, we report the investigation of a multifunctional and non‐stereoselective FMN‐dependent oxidoreductase RubE7 from the rubrolone biosynthetic pathway. Our study outlines a single RubE7‐catalysed sequential reduction of three spatially distinct bonds in a tropolone ring and a reversible double‐bond reduction and dehydrogenation. The crystal structure of IstO (a RubE7 homologue) with 2.0 Å resolution reveals the location of the active site at the interface of two monomers, and the size of active site is large enough to permit both flipping and free rotation of the substrate, resulting in multiple nonselective reduction reactions. Molecular docking and site mutation studies demonstrate that His106 is oriented towards the substrate and is important for the reverse dehydrogenation reaction. [ABSTRACT FROM AUTHOR]

Poly-(butylene adipate-co-terephthalate) (PBAT) has become one of the most prevalent biodegradable plastic film materials owing to its good degradability, mechanical properties, and processability. However, the degradation time of this material was too fast and the functional period was short, which limited its application. Herein, three new tropolone-based UV absorbers (UVA-1C, UVA-4C and UVA-6C) were rationally designed and blended into PBAT. The PBAT/UVA films that formed were used against UV aging and prolonged the functional period of PBAT film. The three new absorbers were synthesized by bridging two tropolones using three different organic chains with different flexibility. Among them, the UVA-6C showed the strongest UV absorbance at around 238 nm and 320 nm. Consequently, the PBAT/UVA-6C film showed an extended validity period of 240 h in the Xenon lamp aging machine and a prolonged functional period of 8 d during the field application test when compared to pure PBAT. More importantly, a 7.8% increase in the maize yield was obtained under PBAT/UVA-6C film relative to pure PBAT film. Obviously, the novel prepared UVA-6C compound is a good candidate for UV absorption in PBAT, which makes PBAT/UVA-6C film more advantageous over pure PBAT in practical applications as biodegradable agricultural film. [ABSTRACT FROM AUTHOR]

While we have come to appreciate the architectural complexity of microbially synthesized secondary metabolites, far less attention has been paid to linking their structural features with possible modes of action. This is certainly the case with tropodithietic acid (TDA), a broad-spectrum antibiotic generated by marine bacteria that engage in dynamic symbioses with microscopic algae. TDA promotes algal health by killing unwanted marine pathogens; however, its mode of action (MoA) and significance for the survival of an algal-bacterial miniecosystem remains unknown. Using cytological profiling, we herein determine the MoA of TDA and surprisingly find that it acts by a mechanism similar to polyether antibiotics, which are structurally highly divergent. We show that like polyether drugs, TDA collapses the proton motive force by a proton antiport mechanism, in which extracellular protons are exchanged for cytoplasmic cations. The α-carboxy-tropone substructure is ideal for this purpose as the proton can be carried on the carboxyl group, whereas the basicity of the tropylium ion facilitates cation export. Based on similarities to polyether anticancer agents we have further examined TDA's cytotoxicity and find it to exhibit potent, broad-spectrum anticancer activities. These results highlight the power of MoA-profiling technologies in repurposing old drugs for new targets. In addition, we identify an operon that confers TDA resistance to the producing marine bacteria. Bioinformatic and biochemical analyses of these genes lead to a previously unknown metabolic link between TDA/acid resistance and the γ-glutamyl cycle. The implications of this resistance mechanism in the context of the algal-bacterial symbiosis are discussed.

Polyoxygenated tropolones possess a broad range of biological activity, and as a result are promising lead structures or fragments for drug development. However, structure–function studies and subsequent optimization have been challenging, in part due to the limited number of readily available tropolones and the obstacles to their synthesis. Oxidopyrylium [5+2] cycloaddition can effectively generate a diverse array of seven‐membered ring carbocycles, and as a result can provide a highly general strategy for tropolone synthesis. Here, we describe the use of 3‐hydroxy‐4‐pyrone‐based oxidopyrylium cycloaddition chemistry in the synthesis of functionalized 3,7‐dimethoxytropolones, 3,7‐dihydroxytropolones, and isomeric 3‐hydroxy‐7‐methoxytropolones through complementary benzyl alcohol‐incorporating procedures. The antiviral activity of these molecules against herpes simplex virus‐1 and hepatitis B virus is also described, highlighting the value of this approach and providing new structure–function insights relevant to their antiviral activity. [ABSTRACT FROM AUTHOR]

Hyperpigmentation is a disorder of facial skin pigments due to an increase in the process of melanogenesis, which can cause a darkening of skin color. A flavonoid compound with potential as a skin-lightening agent is quercetin, commonly found in Moringa oleifera L. leaves. This study aims to determine quercetin’s affinity and molecular mechanism on tyrosinase enzyme target proteins using an in-silico molecular docking method. Docking of quercetin with the tyrosinase enzyme produced a bond energy value of -7.08 kcal/mol. In comparison, the tropolone as a native ligand with the tyrosinase enzyme produced -4.79 kcal/mol. Quercetin has a strong affinity for the tyrosinase enzyme, indicated by the bond energy results from docking. Quercetin extraction from Moringa oleifera L. leaves using three different extraction methods: maceration, soxhlation, and reflux were made. The chromatogram from the TLC-Densitometry method showed the identification result in maceration and soxhlation extract containing quercetin, while reflux extract did not contain quercetin. The highest quercetin was obtained in the maceration method with a level of 21.57% w/w, while the soxhlation received quercetin as much as 18.49% w/w. In-vitro tests were carried out using a spectrophotometric method using a comparison of kojic acid. The in-vitro test found that IC50 from kojic acid was 48.90 μg/mL and IC50 of the extract from moringa leaf maceration of 115.36 μg/mL. Based on this research, quercetin compounds in Moringa oleifera L. leaves from maceration can potentially be skin-lightening agents. [ABSTRACT FROM AUTHOR]

The near-ultraviolet π *← π absorption system of weakly bound complexes formed between tropolone (TrOH) and formic acid (FA) under cryogenic free-jet expansion conditions has been interrogated by exploiting a variety of fluorescence-based laser-spectroscopic probes, with synergistic quantum-chemical calculations built upon diverse model chemistries being enlisted to unravel the structural and dynamical properties of the pertinent ground [X1A′X1A′] and excited [A1A′(π*π)] electronic states. For binary TrOH FA adducts, the presence of dual hydrogen-bond linkages gives rise to three low-lying isomers designated (in relative energy order) as INT, EXT1, and EXT2 depending on whether docking of the FA ligand to the TrOH substrate takes place internal or external to the five-membered reaction cleft of tropolone. While the symmetric double-minimum topography predicted for the INT potential surface mediates an intermolecular double proton-transfer event, the EXT1 and EXT2 structures are interconverted by an asymmetric single proton-transfer process that is TrOH-centric in nature. The A−XA−X origin of TrOH FA at ν00=27-484.45cm−1 is displaced by δν00=+466.76cm−1 with respect to the analogous feature for bare tropolone and displays a hybrid type − a/b rotational contour that reflects the configuration of binding. A comprehensive analysis of vibrational landscapes supported by the optically connected X1A′X1A′ and A1A′(π)A1A′π*π manifolds, including the characteristic isotopic shifts incurred by partial deuteration of the labile TrOH and FA protons, has been performed leading to the uniform assignment of numerous intermolecular (viz., modulating hydrogen-bond linkages) and intramolecular (viz., localized on monomer subunits) degrees of freedom. The holistic interpretation of all experimental and computational findings affords compelling evidence that an external-binding motif (attributed to EXT1), rather than the thermodynamically more stable cleft-bound (INT) form, was the carrier of fluorescence signals observed during the present work. [ABSTRACT FROM AUTHOR]

The alkaloid colchicine represents a prominent lead structure for the development of tubulin‐binding chemotherapeutics. In the course of explorative research into semi‐synthetic colchicinoids we stumbled upon a number of unexpected and mechanistically surprising transformations which reflect the very particular reactivity of the tropolone ether unit and its interplay with adjacent functional groups. Examples are the selective C‐8‐methylation of colchicone upon reaction with the Wittig reagent triphenylphosphonium methylide, the AlMe3‐mediated isomerization of colchicone to a tetracyclic lactone, and the cyanide‐induced reaction of the colchicol‐derived mesylate to a rearranged and ring B‐defunctionalized cyano‐allo‐colchicinoid. Finally, the fragmenting rearrangement of a tetracyclic colchicinoid with BF3⋅OEt2 in the presence of vinyl‐MgBr afforded a tropolonyl difluoroborate under concomitant transfer of an O‐methyl group from ring C to ring A. [ABSTRACT FROM AUTHOR]

The Diels–Alder reactions of tropolone and its conjugate base with N‐methylmaleimide have been explored computationally and experimentally. Previous studies of the [4+2] cycloaddition under basic conditions show that both endo‐ and exo‐products are obtained in similar, but variable amounts. Density functional theory (ωB97X‐D) explorations of potential energy surfaces, and molecular dynamics trajectories show that the reaction involves an ambimodal transition state for the reaction of the ammonium tropolonate with N‐methylmaleimide, and that similar amounts of endo‐ and exo‐products are obtained. The thermal reaction, studied experimentally in detail here for the first time, is predicted to form the endo‐adduct through an ambimodal transition state. The exo‐adduct can be formed from the same transition state, but requires a hydrogen shift, that hinders this reaction dynamically. Longer reaction times give a small excess of the exo‐product, which is thermodynamically more stable. [ABSTRACT FROM AUTHOR]

Reactions of benzyl potassium species with CO are shown to proceed via transient carbene‐like intermediates that can undergo either dimerization or further CO propagation. In a sterically unhindered case, formal dimerization of the carbene is the dominant reaction pathway, as evidenced by the isolation of ((Ph3SiO)(PhCH2)C)22 and PhCH2C(O)CH(OH)CH2Ph 3. Reactions with increasingly sterically encumbered reagents show competitive reaction pathways involving intermolecular dimerization leading to species analogous to 2 and 3 and those containing newly‐formed five‐membered rings tBu2C6H2(C(OSiR3)C(OSiR3)CH2) (R=Me 6, Ph 7). Even further encumbered reagents proceed to either dimerize or react with additional CO to give a ketene‐like intermediates, thus affording a 7‐membered tropolone derivative 14 or the dione (3,5‐tBu2C6H3)3C6H2CH2C(O))215. [ABSTRACT FROM AUTHOR]

Many researchers have widely explored the need to replace the harmful compound hydroquinone in skin-lightening creams with more skin-friendly compounds that can give similar results. Some compounds from the plant kingdom have been shown to possess human tyrosinase inhibitory action with no adverse effect on the skin. In this study, the virtual screen of glabridin, kojic acid, arbutin, niacinamide, ascorbic acid, salicin, lactic acid, glutathione, azelaic acid, linoleic acid, glycolic acid, acclaimed to possess this activity as well as the synthetic compound hydroquinone, as human tyrosinase-related protein 1 inhibitor was investigated using computational methods. Site-directed docking was performed at the binding pocket on the enzyme carrying the cocrystallized ligand tropolone. The binding affinity of salicin (-6.7 kcal/mol), a-arbutin (-6.3 kcal/mol), glutathione (-6.2 kcal/mol), ascorbic acid (-5.7 kcal/mol), and niacinamide (-5.7 kcal/mol) were higher than that of the cocrystallized ligand tropolone (-5.5 kcal/mol) and the synthetic skin lightening compound hydroquinone (-4.8 kcal/mol). a-arbutin and glutathione also interacted with similar amino acids units as hydroquinone, suggesting that they followed the exact mechanism of action. These findings strongly corroborate the claim that these natural products could inhibit melanin production and may serve to replace hydroquinone in skin lightening creams.

The non‐canonical terpene cyclase AsR6 is responsible for the formation of 2E,6E,9E‐humulene during the biosynthesis of the tropolone sesquiterpenoid (TS) xenovulene A. The structures of unliganded AsR6 and of AsR6 in complex with an in crystallo cyclized reaction product and thiolodiphosphate reveal a new farnesyl diphosphate binding motif that comprises a unique binuclear Mg2+‐cluster and an essential K289 residue that is conserved in all humulene synthases involved in TS formation. Structure‐based site‐directed mutagenesis of AsR6 and its homologue EupR3 identify a single residue, L285/M261, that controls the production of either 2E,6E,9E‐ or 2Z,6E,9E‐humulene. A possible mechanism for the observed stereoselectivity was investigated using different isoprenoid precursors and results demonstrate that M261 has gatekeeping control over product formation. [ABSTRACT FROM AUTHOR]

Many researchers have widely explored the need to replace the harmful compound hydroquinone in skin-lightening creams with more skin-friendly compounds that can give similar results. Some compounds from the plant kingdom have been shown to possess human tyrosinase inhibitory action with no adverse effect on the skin. In this study, the virtual screening of glabridin, kojic acid, arbutin, niacinamide, ascorbic acid, salicin, lactic acid, glutathione, azelaic acid, linoleic acid, glycolic acid, acclaimed to possess this activity as well as the synthetic compound hydroquinone, as human tyrosinase-related protein 1 inhibitor was investigated using computational methods. Site-directed docking was performed at the binding pocket on the enzyme carrying the cocrystallized ligand tropolone. The binding afinity of salicin (-6:7 kcal/mol), α-arbutin (-6:3 kcal/mol), glutathione (-6:2 kcal/mol), ascorbic acid (-5:7 kcal/mol), and niacinamide (-5:7 kcal/mol) were higher than that of the cocrystallized ligand tropolone (-5:5 kcal/mol) and the synthetic skin lightening compound hydroquinone (-4:8 kcal/mol). α-arbutin and glutathione also interacted with similar amino acids units as hydroquinone, suggesting that they followed the exact mechanism of action. These findings strongly corroborate the claim that these natural products could inhibit melanin production and may serve to replace hydroquinone in skin lightening creams. [ABSTRACT FROM AUTHOR]

Total biosynthesis in fungi is beginning to compete with traditional chemical total synthesis campaigns. Herein, the advantages, disadvantages and future opportunities are discussed within the scope of several recent examples. 1 Introduction 2 Synthetic Examples 2.1 2-Pyridones 2.2 Cytochalasans 2.3 Sorbicillinoids 2.4 Decalins: Solanapyrone 2.5 α-Pyrone Polyenes: Citreoviridin and Aurovertin 2.6 Anditomin and Related Meroterpenoids 2.7 Tropolone Sesquiterpenoids 3 Conclusion [ABSTRACT FROM AUTHOR]

A Ni/N-heterocyclic carbene catalyst couples diynes to the C(α)-C(β) double bond of tropone, a type of reaction that is unprecedented for metal-catalyzed cycloadditions with aromatic tropone. Many different diynes were efficiently coupled to afford [5-6-7] fused tricyclic products, while [5-7-6] fused tricyclic compounds were obtained as minor byproducts in a few cases. The reaction has broad substrate scope and tolerates a wide range of functional groups, and excellent regioselectivity is found with unsymmetrical diynes. Theoretical calculations show that the apparent enone cycloaddition occurs through a distinctive 8π insertion of tropone. The initial intramolecular oxidative cyclization of diyne produces the nickelacyclopentadiene intermediate. This intermediate undergoes an 8π insertion of tropone, and subsequent reductive elimination generates the [5-6-7] fused tricyclic product. This initial product undergoes two competing isomerizations, leading to the observed [5-6-7] and [5-7-6] fused tricyclic products.

The title compound, 2-(methylamino)cyclohepta-2,4,6-trien-1-one, C8H9NO, crystallizes in the monoclinic space group P21/c, with three independent molecules in the asymmetric unit. The planarity of the molecules is indicated by planes fitted through the seven ring carbon atoms. Small deviations from the planes, with an extremal r.m.s. deviation of 0.0345 Å, are present. In complexes of transition metals with similar ligands, the large planar seven-membered aromatic rings have shown to improve the stability of the complex. Two types of hydrogen-bonding interactions, C—H...O and N—H...O, are observed, as well as bifurcation of these interactions. The N—H...O interactions link molecules to form infinite chains. The packing of molecules in the unit cell shows a pattern of overlapping aromatic rings, forming column-like formations. π–π interactions are observed between the overlapping aromatic rings at 3.4462 (19) Å from each other.

The discovery of allosteric modulators is a multi-disciplinary approach, which is time- and cost-intensive. High-throughput screening combined with novel computational tools can reduce these factors. Thus, we developed an enzyme activity assay, which can be included in the drug discovery work-flow subsequent to the in-silico library screening. While the in-silico screening yields in the identification of potential allosteric modulators, the developed in-vitro assay allows for the characterisation of them. Candida rugosa lipase (CRL), a glyceride hydrolysing enzyme, has been selected for the pilot development. The assay conditions were adjusted to CRL’s properties including pH, temperature and substrate specificity for two different substrates. The optimised assay conditions were validated and were used to characterise Tropolone, which was identified as an allosteric modulator. In conclusion, the assay is a reliable, reproducible, and robust tool, which can be streamlined with in-silico screening and incorporated in an automated high-throughput screening workflow.

This review summarises the known structures, biological activities, and biosynthetic pathways of the tropolone sesquiterpenoid family of fungal secondary metabolites. Synthesis of this knowledge allows likely structural and stereochemical misassignments to be revised and shows how the compounds can be divided into three main biosynthetic classes based on the stereochemistry of key biosynthetic steps.

Radical cyclization reactions are still a challenging field in synthetic organic chemistry. Herein, the radical reactions of 6‐ and 7‐membered diosphenol derivatives (tropolone) with a significant difference in reactivity, ring size, aromaticity and stability were investigated. While the former produces a mixture of products including oxabicycloalkanones, the experimental work performed herein resulted with a single 2‐(3‐hydroxypropyl)cyclohepta‐2,4,6‐trienone product, regioselectively. DFT calculations (UM05/6‐311++G(d,p)) were performed following the experimental studies in order to describe the outcomes correctly. Therefore, all possible reaction pathways were investigated for both diosphenol and tropolone. The reaction barriers and intrinsic barriers from the Marcus theory were calculated to investigate the thermodynamic and intrinsic electronic effects to the experimental product distribution. Both experiment and theory show that the aforementioned systems have different selectivity routes governed by several factors. As a result of this comparative study, the charge distribution at the reactive atoms, entropy factors for cyclization vs termination and aromatization of the ring effects were found to be the driving factors for the observed regioselectivity. [ABSTRACT FROM AUTHOR]

Hinokitiol has a broad antibacterial activity against bacteria and fungi. While its biosynthetic pathway has been intensively studied, its dynamics in natural environments, such as biodegradation pathway, remain unclear. In this study, the authors report a direct deuterium labeling of hinokitiol as a traceable molecular probe to serve those studies. Hinokitiol was subjected to the H2-Pd/C-D2O conditions and deuterated hinokitiol was obtained with excellent deuteration efficiencies and in moderate yield. The 1H and 2H NMR spectra indicated that all ring- and aliphatic hydrogens except that on C-6 were substituted by deuterium. According to the substrate scope and computational chemistry, deuteration on tropolone ring was suggested to proceed via D+-mediated process, and which was supported by the results of the experiment with trifluoroacetic acid and Pd(TPP)4. On the other hand, the deuteration on aliphatic group was predicted to be catalyzed by Pd(II) species. [ABSTRACT FROM AUTHOR]

Colchicine is light-sensitive and undergoes electrocyclic reaction upon exposure to light. In this study, the photostability of colchicine was found to be significantly improved via rebalancing the electron density of the tropolone ring system after solid form changes. This work may provide a new approach for resolving photo-sensitive challenges during drug development. [ABSTRACT FROM AUTHOR]

Tropolone reacts with amino acids to form adducts that generate contrast on highly fluorescent paper surfaces upon UV irradiation. Furthermore, the conjugated seven-membered ring of tropolone enables secondary chemical treatments; demonstrated here using two diazonium salts, 4-methoxybenzenediazonium tetrafluoroborate (4MBD) and 4-nitrobenzenediazonium tetrafluoroborate (4NBD). These produce yellow and red dyed fingermarks, respectively. While tropolone treatment is rapid to effect and compatible with ninhydrin in a detection sequence, the methodology proved less effective than current chemical visualisation treatments. Nevertheless, this work unambiguously demonstrates the reactivity of tropolone towards fingermark residues and may inspire future generations of non-benzenoid chemical visualisation treatments.

HIV-RT is an essential enzyme for HIV replication it comprises two associated functions: RNA- and DNA-dependent DNA polymerase (RDDP & DDDP) and ribonuclease H (RNase H). The RNase H is function to cleave RNA strand in RNA/DNA hybrid intermediate in the reverse transcription process. Currently, successful inhibitors target the polymerase function of HIV-RT. RNase H evolves to be a promising target for anti-HIV drug research. This review describes the compounds reported as HIV-1 RNase H inhibitors.

Tropolone sesquiterpenoids (TS) are an intriguing family of biologically active fungal meroterpenoids that arise through a unique intermolecular hetero Diels–Alder (hDA) reaction between humulene and tropolones. Here, we report on the combinatorial biosynthesis of a series of unprecedented analogs of the TS pycnidione 1 and xenovulene A 2. In a systematic synthetic biology driven approach, we recombined genes from three TS biosynthetic gene clusters (pycnidione 1, xenovulene A 2 and eupenifeldin 3) in the fungal host Aspergillus oryzae NSAR1. Rational design of the reconstituted pathways granted control over the number of hDA reactions taking place, the chemical nature of the fused polyketide moiety (tropolono‐ vs. monobenzo‐pyranyl) and the degree of hydroxylation. Formation of unexpected monobenzopyranyl sesquiterpenoids was investigated using isotope‐feeding studies to reveal a new and highly unusual oxidative ring contraction rearrangement. [ABSTRACT FROM AUTHOR]

Tropolon‐Sesquiterpenoide (TS) sind eine faszinierende Familie biologisch aktiver pilzlicher Meroterpenoide, die durch eine einzigartige intermolekulare Hetero‐Diels‐Alder (hDA)‐Reaktion zwischen Humulen und Tropolonen entstehen. Hier berichten wir über die kombinatorische Biosynthese einer Reihe beispielloser Analoga von Pycnidione 1 und Xenovulene A 2. In einem systematischen auf synthetischer Biologie basierendem Ansatz haben wir Gene aus drei Biosynthesegenclustern (Pycnidione 1, Xenovulene A 2 und Eupenifeldin 3) im pilzlichen Wirt Aspergillus oryzae NSAR1 rekombiniert. Das rationale Design der rekonstituierten Biosynthesewege ermöglichte die Kontrolle über die Anzahl der stattfindenden hDA‐Reaktionen, die chemische Natur der kondensierten Polyketideinheit (Tropolono‐ vs. Monobenzopyranyl) und den Hydroxylierungsgrad. Die Bildung unerwarteter Monobenzopyranylsesquiterpenoide wurde mithilfe von Isotopenfütterungsstudien untersucht und führte zur Entdeckung einer neuen und höchst ungewöhnlichen oxidativen Ringkontraktion. [ABSTRACT FROM AUTHOR]

• HDAC6 is upregulated in penumbra neurons and astrocytes after photothrombosis. • HDAC6 co-localizes with apoptotic cells in penumbra after photothrombotic stroke. • HDAC6 inhibitor HPOB and sodium valproate show neuroprotector activity. • HDAC2/8 inhibitor α-phenyl tropolone reduces apoptosis and stroke-induced infarct. • HDAC3 inhibitor BRD3308, or HDAC4 inhibitor LMK235 have no neuroprotector activity. Epigenetic processes play important roles in brain responses to ischemic injury. We studied effects of photothrombotic stroke (PTS, a model of ischemic stroke) on the intracellular level and cellular localization of histone deacetylases HDAC3, HDAC4 and HDAC6 in the rat brain cortex, and tested the potential neuroprotector ability of their inhibitors. The background level of HDAC3, HDAC4 and HDAC6 in the rat cerebral cortex was relatively low. HDAC3 localized in the nuclei of some neurons and few astrocytes. HDAC4 was found in the neuronal cytoplasm. After PTS, their levels in penumbra did not change, but HDAC4 appeared in the nuclei of some cells. Its level in the cytoplasmic, but not nuclear fraction of penumbra decreased at 24, but not 4 h after PTS. HDAC6 was upregulated in neurons and astrocytes in the PTS-induced penumbra, especially in the nuclear fraction. Unlike HDAC3 and HDAC4, HDAC6 co-localized with TUNEL-positive apoptotic cells. Inhibitory analysis confirmed the involvement of HDAC6, but not HDAC3 and HDAC4 in neurodegeneration. HDAC6 inhibitor HPOB, HDAC2/8 inhibitor α-phenyl tropolone, and non-specific histone deacetylase inhibitor sodium valproate, but not HDAC3 inhibitor BRD3308, or HDAC4 inhibitor LMK235, decreased PTS-induced infarction volume in the mouse brain, reduced apoptosis, and recovered the motor behavior. HPOB also restored PTS-impaired acetylation of α-tubulin. α-phenyl tropolone restored acetylation of histone H4 in penumbra cells. These results suggest that histone deacetylases HDAC6 and HDAC2 are the possible molecular targets for anti-ischemic therapy, and their inhibitors α-phenyl tropolone, HBOP and sodium valproate can be considered as promising neuroprotectors. [ABSTRACT FROM AUTHOR]