Seven-membered Ring Structure Research Articles

Engineering Streptomyces sp. CPCC 204095 for the targeted high-level production of isatropolone A by elucidating its pathway-specific regulatory mechanism

BackgroundIsatropolone 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.ResultsHere 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.ConclusionIn 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.

Vibrational spectroscopy of aniline cations and their H-loss cations in helium droplets

We produced aniline cations (c–C6H5NH2+) and their dehydro- (H-loss) cations inside helium droplets by electron ionization and observed their mass-selected vibrational spectra in the NH stretching region. We observed vibrational bands at m/q = 93 which were identified as aniline cations. These bands showed only a few cm−1 shifts from the symmetric and anti-symmetric NH stretching bands for the amino (NH2) group in the gas phase. For the H-loss cation at mass m/q = 92, the agreement of the observed NH band frequency with the result of DFT calculations suggests several candidate species, including a seven-membered ring structure, 4-monodehydro azepinylium (c–C6NH6+). A new reaction pathway to this cation was discussed by considering large excess energy in the ionization process.

A Novel Hydrophobic Polyimide Film with Sag Structure Derived from Multi-Hybrid Strategy.

Polyimide (PI) film with hydrophilic greatly limits their application in the field of microelectronic device packaging. A novel hydrophobic PI film with sag structure and improved mechanical properties is prepared relying on the reaction between anhydride-terminated isocyanate-based polyimide (PIY) containing a seven-membered ring structure and the amino-terminated polyamide acid (PAA) via multi-hybrid strategy, this work named it as hybrid PI film and marked it as PI-PIY-X. PI-PIY-30 showed excellent hydrophobic properties, and the water contact angle could reach to 102°, which is 20% and 55% higher than simply PI film and PIY film, respectively. The water absorption is only 1.02%, with a decrease of 49% and 53% compared with PI and PIY. Due to that the degradation of seven-membered ring and generation of carbon dioxide led to the formation of sag structure, the size of sag structures is ≈16.84 and 534.55nm for in-plane and out-plane direction, which are observed on surface of PI-PIY-30. Meanwhile, PI-PIY-30 possessed improved mechanical properties, and the tensile strength is 109.08MPa, with 5% and more than 56% higher than that of pure PI and PIY film, showing greatly application prospects in the field of integrated circuit.

Synthesis and characterization of supramolecular assembly probenecid cocrystal

To improve the bioavailability and provide a lead compound for developing formulations of the highly water-insoluble prodrug probenecid (PRO), enhancing its solubility is a crucial challenge that needs to be addressed. Herein, we report the synthesis and solid-state characterization of a new pharmaceutical cocrystal, PRO-BPE, synthesized using trans-1,2-bis(4-pyridyl)ethylene (BPE) to improve the solubility of PRO. The PRO-BPE cocrystals were characterized using various analytical techniques, including differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, Fourier transform-infrared spectroscopy, and X-ray powder diffraction. Single-crystal X-ray diffraction was performed to determine the crystal structure of PRO-BPE. PRO-BPE crystallized in the triclinic crystal system P-1 space group and its asymmetric unit consists of half a BPE molecule and one PRO molecule. The N1 atoms located at both ends of the BPE molecule form stable hydrogen bonds with two PRO carboxyl hydrogens through N1···H4—O4 (1.777 Å, 166.78°) interactions, whereas the O3 atoms of the carboxylic groups form C1—H1···O3 (2.479 Å, 132.10°) hydrogen bonds with two pyridyl hydrogens, resulting in a stable seven-membered ring structure. Furthermore, these fragments are further assembled via C—H···O intermolecular interactions to form a two-dimensional layered structure. Interestingly, the two pyridyl rings of each BPE molecule engage in π···π interactions with the benzene rings of two other non-coplanar PRO molecules. Finally, a three-dimensional framework structure is formed through intramolecular non-covalent interactions. Comprehensive characterization analyses provided further information regarding PRO-BPE cocrystal formation. Based on the equilibrium solubility results, the water solubility of the PRO-BPE cocrystal was superior to that of pure PRO, with an increase of 2.43 times. In summary, this study provides the first evidence that cocrystals could enhance the solubility of PRO and offers valuable insights into the solid-state properties of PRO-BPE cocrystals.

Tropolones and Thailandepsin B as Lead-like Natural Compounds in the Development of Potent and Selective Histone Deacetylase Inhibitors.

Tropolone and thailandepsin B are naturally occurring substances that are primarily isolated from fungi and plants, although they can also be found in certain bacteria. Tropolones belong to an important class of aromatic compounds with a seven-membered nonbenzenoid ring structure. Thailandepsins are a group of natural products that were initially discovered in the culture broth of the Gram-negative bacterium Burkholderia thailandensis. Tropolonebased structures have been identified in over 200 natural compounds, ranging from simple tropolone derivatives to complex multicyclic systems like pycnidione and pyrerubrine A. These natural compounds exhibit a diverse range of pharmacological effects, including antibacterial, antifungal, insecticidal, phytotoxic, anti-inflammatory, antimitotic, anti-diabetic, enzyme inhibitory, anticancer, cytoprotective, and ROS scavenging properties. It is worth noting that thujaplicane, a compound similar to tropolone, displays all of the listed biological activities except for antimitotic action, which has only been observed in one natural tropolone compound, colchicine. Tropolone can be synthesized from commercially available seven-membered rings or derived through various cyclization and cycloaddition reactions. Thailandepsin B, on the other hand, can be synthesized by macro-lactonization of the corresponding secoacid, followed by the formation of internal disulfide bonds. It is important to mention that thailandepsin B exhibits different selective inhibition profiles compared to FK228. We investigated the HDAC inhibitory activity of the Tropolones and Thailandepsin B and discussed the biosynthesis of the naturally occurring compounds and their synthetic scheme. It has been observed that Tropolone derivatives act as isoenzyme-selective inhibitors of proven anticancer drug targets, histone deacetylases (HDACs). Some monosubstituted tropolones show remarkable levels of selectivity for HDAC2 and strongly inhibit the growth of T-lymphocyte cell lines. And Thailandepsins have different selective inhibition profiles than FK228. They exhibit comparable inhibitory activities to FK228 against human HDAC1, HDAC2, HDAC3, HDAC6, HDAC7, and HDAC9, but less potent inhibitory activities than FK228 toward HDAC4 and HDAC8, the latter of which may be useful. Thailandepsins possess potent cytotoxic activities toward some types of cell lines.

The stereoselective synthesis of cis- and trans-fused pyrrolidine containing bicyclic azepine and oxepine derivatives using aza-Cope rearrangement-Mannich cyclization as a key step

The development of novel methods and strategies for the formation of fused five-, six-, and seven-membered ring structures is of utmost importance in organic syntheses.

Chemical syntheses and salient features of azulene-containing homo- and copolymers.

Azulene is a non-alternant, aromatic hydrocarbon with many exciting characteristics such as having a dipole moment, bright color, stimuli responsiveness, anti-Kasha photophysics, and a small HOMO–LUMO gap when compared to its isomer, naphthalene. These properties make azulene-containing polymers an intriguing entity in the field of functional polymers, especially for organic electronic applications like organic field-effect transistors (OFET) and photovoltaic (PV) cells. Since azulene has a fused five and seven-membered ring structure, it can be incorporated onto the polymer backbone through either of these rings or by involving both the rings. These azulene-connection patterns can influence the properties of the resulting polymers and the chemical synthesis in comparison to the electrochemical synthesis can be advantageous in obtaining desired patterns of substitution. Hence, this review article presents a comprehensive overview of the developments that have taken place in the last three decades in the field of chemical syntheses of azulene-containing homo- and copolymers, including brief descriptions of their key properties.

The Effects of pH on the Structure and Bioavailability of Imidazobenzodiazepine-3-Carboxylate MIDD0301.

We describe the effects of pH on the structure and bioavailability of MIDD0301, an oral lead compound for asthma. MIDD0301 interacts with peripheral GABAA receptors to reduce lung inflammation and airway smooth muscle constriction. The structure of MIDD0301 combines basic imidazole and carboxylic acid function in the same diazepine scaffold, resulting in high solubility at neutral pH. Furthermore, we demonstrated that MIDD0301 can interconvert between a seven-membered ring structure at neutral pH and an acyclic compound at or below pH 3. Both structures have two stable conformers in solution that can be observed by 1H NMR at room temperature. Kinetic analysis showed opening and closing of the seven-membered ring of MIDD0301 at gastric and intestinal pH, occurring with different rate constants. However, in vivo studies showed that the interconversion kinetics are fast enough to yield similar MIDD0301 blood and lung concentrations for neutral and acidic formulations. Importantly, acidic and neutral formulations of MIDD0301 exhibit high lung distribution with low concentrations in brain. These findings demonstrate that MIDD0301 interconverts between stable structures at neutral and acidic pH without changes in bioavailability, further supporting its formulation as an oral asthma medication.

Exploiting Substrate Promiscuity of Ectoine Hydroxylase for Regio- and Stereoselective Modification of Homoectoine.

Extant enzymes are not only highly efficient biocatalysts for a single, or a group of chemically closely related substrates but often have retained, as a mark of their evolutionary history, a certain degree of substrate ambiguity. We have exploited the substrate ambiguity of the ectoine hydroxylase (EctD), a member of the non-heme Fe(II)-containing and 2-oxoglutarate-dependent dioxygenase superfamily, for such a task. Naturally, the EctD enzyme performs a precise regio- and stereoselective hydroxylation of the ubiquitous stress protectant and chemical chaperone ectoine (possessing a six-membered pyrimidine ring structure) to yield trans-5-hydroxyectoine. Using a synthetic ectoine derivative, homoectoine, which possesses an expanded seven-membered diazepine ring structure, we were able to selectively generate, both in vitro and in vivo, trans-5-hydroxyhomoectoine. For this transformation, we specifically used the EctD enzyme from Pseudomonas stutzeri in a whole cell biocatalyst approach, as this enzyme exhibits high catalytic efficiency not only for its natural substrate ectoine but also for homoectoine. Molecular docking approaches with the crystal structure of the Sphingopyxis alaskensis EctD protein predicted the formation of trans-5-hydroxyhomoectoine, a stereochemical configuration that we experimentally verified by nuclear-magnetic resonance spectroscopy. An Escherichia coli cell factory expressing the P. stutzeri ectD gene from a synthetic promoter imported homoectoine via the ProU and ProP compatible solute transporters, hydroxylated it, and secreted the formed trans-5-hydroxyhomoectoine, independent from all currently known mechanosensitive channels, into the growth medium from which it could be purified by high-pressure liquid chromatography.

Theoretical Investigations on the Reactivity of Methylidyne Radical toward 2,3,7,8-Tetrachlorodibenzo-p-Dioxin: A DFT and Molecular Dynamics Study.

To explore the potential reactivity of the methylidyne radical (CH) toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the reaction mechanism between them has been systematically investigated employing the density functional theory (DFT) and ab initio molecular dynamics simulations. The relevant thermodynamic and kinetic parameters in the possible reaction pathways have been discussed as well as the IR spectra and hyperfine coupling constants (hfcc’s) of the major products. Different from the reaction of the CH radical with 2,3,7,8-tetrachlorodibenzofuran, CH radical can attack all the C-C bonds of TCDD to form an initial intermediate barrierlessly via the cycloaddition mechanism. After then, the introduced C-H bond can be further inserted into the C-C bond of TCDD, resulting in the formation of a seven-membered ring structure. The whole reactions are favorable thermodynamically and kinetically. Moreover, the major products have been verified by ab initio molecular dynamics simulations. The distinct IR spectra and hyperfine coupling constants of the major products can provide some help for their experimental detection and identification. In addition, the reactivity of the CH radical toward the F- and Br-substituted TCDDs has also been investigated. Hopefully, the present findings can provide new insights into the reactivity of the CH radical in the transformation of TCDD-like dioxins.

Proteasome inhibition by new dual warhead containing peptido vinyl sulfonyl fluorides

The success of inhibition of the proteasome by formation of covalent bonds is a major victory over the long held-view that this would lead to binding the wrong targets and undoubtedly lead to toxicity. Great challenges are now found in uncovering ensembles of new moieties capable of forming long lasting ties. We have introduced peptido sulfonyl fluorides for this purpose. Tuning the reactivity of this electrophilic trap may be crucial for modulating the biological action. Here we describe incorporation of a vinyl moiety into a peptido sulfonyl fluoride backbone, which should lead to a combined attack of the proteasome active site threonine on the double bond and the sulfonyl fluoride. Although this led to strong proteasome inhibitors, in vitro studies did not unambiguously demonstrate the formation of the proposed seven-membered ring structure. Possibly, formation of a seven-membered covalent adduct with the proteosomal active site threonine can only be achieved within the context of the enzyme. Nevertheless, this dual warhead concept may provide exclusive possibilities for duration and selectivity of proteasome inhibition.

First-principles studies on graphene-supported transition metal clusters.

Theoretical studies on the structure, stability, and magnetic properties of icosahedral TM13 (TM = Fe, Co, Ni) clusters, deposited on pristine (defect free) and defective graphene sheet as well as graphene flakes, have been carried out within a gradient corrected density functional framework. The defects considered in our study include a carbon vacancy for the graphene sheet and a five-membered and a seven-membered ring structures for graphene flakes (finite graphene chunks). It is observed that the presence of defect in the substrate has a profound influence on the electronic structure and magnetic properties of graphene-transition metal complexes, thereby increasing the binding strength of the TM cluster on to the graphene substrate. Among TM13 clusters, Co13 is absorbed relatively more strongly on pristine and defective graphene as compared to Fe13 and Ni13 clusters. The adsorbed clusters show reduced magnetic moment compared to the free clusters.

Stable Incorporation of ATPase Subunits into 19 S Regulatory Particle of Human Proteasome Requires Nucleotide Binding and C-terminal Tails

The 26 S proteasome is a large multi-subunit protein complex that degrades ubiquitinated proteins in eukaryotic cells. Proteasome assembly is a complex process that involves formation of six- and seven-membered ring structures from homologous subunits. Here we report that the assembly of hexameric Rpt ring of the 19 S regulatory particle (RP) requires nucleotide binding but not ATP hydrolysis. Disruption of nucleotide binding to an Rpt subunit by mutation in the Walker A motif inhibits the assembly of the Rpt ring without affecting heterodimer formation with its partner Rpt subunit. Coexpression of the base assembly chaperones S5b and PAAF1 with mutant Rpt1 and Rpt6, respectively, relieves assembly inhibition of mutant Rpts by facilitating their interaction with adjacent Rpt dimers. The mutation in the Walker B motif which impairs ATP hydrolysis does not affect Rpt ring formation. Incorporation of a Walker B mutant Rpt subunit abrogates the ATPase activity of the 19 S RP, suggesting that failure of the mutant Rpt to undergo the conformational transition from an ATP-bound to an ADP-bound state impairs conformational changes in the other five wild-type Rpts in the Rpt ring. In addition, we demonstrate that the C-terminal tails of Rpt subunits possessing core particle (CP)-binding affinities facilitate the cellular assembly of the 19 S RP, implying that the 20 S CP may function as a template for base assembly in human cells. Taken together, these results suggest that the ATP-bound conformational state of an Rpt subunit with the exposed C-terminal tail is competent for cellular proteasome assembly.

Formation of Organoxenon Dications in the Reactions of Xenon with Dications Derived from Toluene

The bimolecular reactivity of xenon with C(7)H(n)(2+) dications (n=6-8), generated by double ionization of toluene using both electrons and synchrotron radiation, is studied by means of a triple-quadrupole mass spectrometer. Under these experimental conditions, the formation of the organoxenon dications C(7)H(6)Xe(2+) and C(7)H(7)Xe(2+) is observed to occur by termolecular collisional stabilization. Detailed experimental and theoretical studies show that the formation of C(7)H(6)Xe(2+)+H(2) from doubly ionized toluene (C(7)H(8)(2+)) and xenon occurs as a slightly endothermic, direct substitution of dihydrogen by the rare gas with an expansion to a seven-membered ring structure as the crucial step. For the most stable isomer of C(7)H(6)Xe(2+), an adduct between the cycloheptatrienyldiene dication and xenon, the computed binding energy of 1.36 eV reaches the strength of (weak) covalent bonds. Accordingly, electrophiles derived from carbenes might be particularly promising candidates in the search for new rare-gas compounds.

Synthesis and characterisation of new molybdenum – oxo complexes containing diphenylphosphinylacetic acid and 2-(tert-butylsulphoxide)phenyldiphenylphosphine oxide as bidentate ligands

Reaction of the ligands diphenylphosphinylacetic acid Ph 2P(O)CH 2COOH ( 1) and 2-(tert-butylthio)phenyldiphenylphosphine oxide Ph 2P(O)C 6H 4 tBuS ( 2) with “MoO 2Cl 2”, resulted in two complexes MoO 2Cl 2Ph 2P(O)CH 2COOH ( 3) and MoO 2Cl 2Ph 2P(O)C 6H 4 tBuS(O) ( 4). Complexes 3 and 4 were isolated and analysed by 1H NMR, 31P NMR and X-ray crystallography. Complex 3 crystallised with a molecule of the free ligand in a 1:1 ratio ( 3· 1) and complex 4 crystallised with molecules of the solvent CH 2Cl 2 within the unit cell in a 2:1 ratio ( 4·0.5 CH 2 Cl 2). Tetrameric arrangements comprised of hydrogen bonds were observed in complexes 1 and 3. Complex 4 exhibited a seven-membered ring structure owing to the oxidation of the sulphide in 2 to sulphoxide and coordination of this ligand via the oxygen atoms to the molybdenum atom.

A practical method to access enantiopure β-perfluoroalkyl-β-amino acids: diastereoselective reduction of cyclic enamino-esters

A highly practical method to access enantiopure β-perfluoroalkyl-β-amino acids was developed, which could be conducted without any expensive reagent, special apparatus/technique, nor tedious chromatographic separation. The condensation of methyl 4,4,4-trifluoro-3-oxobutanoate with ( S)-2-amino-2-phenylethanol, followed by an intramoleculer transesterification, gave an enamino-ester with a seven-membered ring structure. The hydride reduction of the cyclic enamino-ester proceeded with excellent diastereoselectivity (dr = 95:5–97:3) to give the corresponding cyclic amino-ester. The major isomer of the cyclic amino-ester was readily separated from the minor one and successfully converted into ( S)-3-amino-4,4,4-trifluorobutanoic acid (five steps, 38% overall yield, >99% ee). Concerning the key step of this synthesis, the same strategy was applicable to another substrate; the asymmetric hydride reduction of a cyclic enamino-ester with a pentafluoroethyl group also proceeded in excellent diastereoselectivity (dr = 96:4).

Synthesis and in vitro cytotoxicity of novel hydrophilic chiral 2-alkoxy-1,4-butanediamine platinum (II) complexes

Twenty-six new hydrophilic chiral 2-alkoxy-1,4-butanediamine platinum (II) complexes having a seven-membered ring structure between a bidentate carrier ligand and a platinum atom have been synthesized and most of them were evaluated for their in vitro cytotoxicity toward A549 human non-small cell lung carcinoma and HCT-116 human colon cancer cell lines. The cytotoxicities of platinum complexes are related to the nature of the carrier ligand and leaving group. Complex 5′b, viz. cis-dichloro[(2 R)-ethoxy-1,4-butanediamine] platinum (II), exhibits the greatest potency among those 21 tested platinum complexes in both cell lines.

Biosynthetic Pathway of β-Thujaplicin in the Cupressus lusitanica Cell Culture

Summary The biosynthesis pathway of β-thujaplicin,which has a unique conjugated seven-membered ring structure, was investigated using the Cupressus lusitanica cell culture. We also examined a transformation of the carbon skeleton during its biosynthesis. Incorporation of [10- 14 C] geraniol into β-thujaplicin in the cell culture revealed that this compound was biosynthesized via geranylpyrophosphate (GPP) and hence is a monoterpenoid. The biosynthesis pathway from glucose to GPP and a skeletal rearrangement of GPP to β-thujaplicin are proposed, based on the NMR analysis of β-thujaplicin biosynthesized in C. lusitanica cells from [1- 13 C]-, [2- 13 C]- and [U- 13 C]-glucose. β-Thujaplicin was produced in the C. lusitanica cell from GPP, which was almost solely produced through the GAP/pyruvate pathway; contribution of the classical mevalonate pathway must be negligible, contrary to our previous conclusion. In addition, it was assumed that GPP was transformed to β-thujaplicin via the limonane type skeleton, which is a common intermediate of cyclic monoterpene.

11B NMR Spectroscopic Observation of a Borate Ion–Diol Complex with a Seven-Membered Ring and Comparison of Stability among Complexes with Different Ring Sizes

Abstract A 11B NMR signal, which corresponded to a 1 : 1 complex of the borate ion and 1,4-butanediol (considered to have a seven-membered ring structure), was observed in aqueous solutions. The stability of the complex was lower than those of complexes with five- or six-membered rings between borate ions and structurally similar diols.

Synthesis and in vitro cytotoxicity of 1,3-dioxolane-2-(2-ethanamine)-2-methanamine platinum(II) complexes

The synthesis and in vitro cytotoxicity of novel 1,3-dioxolane-2-(2-ethanamine)-2-methanamine platinum(II) complexes having a seven-membered ring structure are described. It has been demonstrated that cisplatin-resistant murine L1210 leukemia cells have lower cross-resistance to this class of compounds than to cisplatin and carboplatin, and the human stomach cancer cell lines, SNU-1, SNU-5, and SNU-16, are highly sensitive to the members of this class.