Dual-purpose isocyanides produced by Aspergillus fumigatus contribute to cellular copper sufficiency and exhibit antimicrobial activity.

The maintenance of sufficient but nontoxic pools of metal micronutrients is accomplished through diverse homeostasis mechanisms in fungi. Siderophores play a well established role for iron homeostasis; however, no copper-binding analogs have been found in fungi. Here we demonstrate that, in Aspergillus fumigatus, xanthocillin and other isocyanides derived from the xan biosynthetic gene cluster (BGC) bind copper, impact cellular copper content, and have significant metal-dependent antimicrobial properties. xan BGC-derived isocyanides are secreted and bind copper as visualized by a chrome azurol S (CAS) assay, and inductively coupled plasma mass spectrometry analysis of A. fumigatus intracellular copper pools demonstrated a role for xan cluster metabolites in the accumulation of copper. A. fumigatus coculture with a variety of human pathogenic fungi and bacteria established copper-dependent antimicrobial properties of xan BGC metabolites, including inhibition of laccase activity. Remediation of xanthocillin-treated Pseudomonas aeruginosa growth by copper supported the copper-chelating properties of xan BGC isocyanide products. The existence of the xan BGC in several filamentous fungi suggests a heretofore unknown role of eukaryotic natural products in copper homeostasis and mediation of interactions with competing microbes.

Chemoenzymatic Buta-1,3-diene Synthesis from Syngas Using Biological Decarboxylative Claisen Condensation and Zeolite-Based Dehydration.

A method for producing buta-1,3-diene (1,3-BD) by an amalgamation of chemical and biological approaches with syngas as the carbon source is proposed. Syngas is converted to the central intermediate, acetyl-CoA, by microorganisms through a tetrahydrofolate metabolism pathway. Acetyl-CoA is subsequently converted to malonyl-CoA using a carbonyl donor in the presence of a carboxylase enzyme. A decarboxylative Claisen condensation of malonyl-CoA and acetaldehyde ensues in the presence of acyltransferases to form 3-hydroxybutyryl-CoA, which is subsequently reduced by aldehyde reductase to give butane-1,3-diol (1,3-BDO). An ensuing dehydration step converts 1,3-BDO to 1,3-BD in the presence of a chemical dehydrating reagent.

Pd-Catalyzed Decarboxylative Olefination: Stereoselective Synthesis of Polysubstituted Butadienes and Macrocyclic P-glycoprotein Inhibitors.

The efficient and stereoselective synthesis of polysubstituted butadienes, especially the multifunctional butadienes, represents a great challenge in organic synthesis. Herein, we wish to report a distinctive Pd(0) carbene-initiated decarboxylative olefination approach that enables the direct coupling of diazo esters with vinylethylene carbonates (VECs), vinyl oxazolidinones, or vinyl benzoxazinones to afford alcohol-, amine-, or aniline-containing 1,3-dienes in moderate to high yields and with excellent stereoselectivity. This protocol features operational simplicity, mild reaction conditions, a broad substrate scope, and gram-scalability. Notably, a structurally unique allylic Pd(II) intermediate was isolated and characterized. DFT calculation and control experiments demonstrated that a rare Pd(0) carbene intermediate could be involved in this reaction. Moreover, the polysubstituted butadienes as novel building blocks were unprecedentedly assembled into macrocycles, which efficiently inhibited the P-glycoprotein and dramatically reversed multidrug resistance in cancer cells by 190-fold.

The organ-specific differential roles of rice DXS and DXR, the first two enzymes of the MEP pathway, in carotenoid metabolism in Oryza sativa leaves and seeds.

BACKGROUND: Deoxyxylulose 5-phosphate synthase (DXS) and deoxyxylulose 5-phosphate reductoisomerase (DXR) are the enzymes that catalyze the first two enzyme steps of the methylerythritol 4-phosphate (MEP) pathway to supply the isoprene building-blocks of carotenoids. Plant DXR and DXS enzymes have been reported to function differently depending on the plant species. In this study, the differential roles of rice DXS and DXR genes in carotenoid metabolism were investigated. RESULTS: The accumulation of carotenoids in rice seeds co-expressing OsDXS2 and stPAC was largely enhanced by 3.4-fold relative to the stPAC seeds and 315.3-fold relative to non-transgenic (NT) seeds, while the overexpression of each OsDXS2 or OsDXR caused no positive effect on the accumulation of either carotenoids or chlorophylls in leaves and seeds, suggesting that OsDXS2 functions as a rate-limiting enzyme supplying IPP/DMAPPs to seed carotenoid metabolism, but OsDXR doesn't in either leaves or seeds. The expressions of OsDXS1, OsPSY1, OsPSY2, and OsBCH2 genes were upregulated regardless of the reductions of chlorophylls and carotenoids in leaves; however, there was no significant change in the expression of most carotenogenic genes, even though there was a 315.3-fold increase in the amount of carotenoid in rice seeds. These non-proportional expression patterns in leaves and seeds suggest that those metabolic changes of carotenoids were associated with overexpression of the OsDXS2, OsDXR and stPAC transgenes, and the capacities of the intermediate biosynthetic enzymes might be much more important for those metabolic alterations than the transcript levels of intermediate biosynthetic genes are. Taken together, we propose a 'Three Faucets and Cisterns Model' about the relationship among the rate-limiting enzymes OsDXSs, OsPSYs, and OsBCHs as a "Faucet", the biosynthetic capacity of intermediate metabolites as a "Cistern", and the carotenoid accumulations as the content of "Cistern". CONCLUSION: Our study suggests that OsDXS2 plays an important role as a rate-limiting enzyme supplying IPP/DMAPPs to the seed-carotenoid accumulation, and rice seed carotenoid metabolism could be largely enhanced without any significant transcriptional alteration of carotenogenic genes. Finally, the "Three Faucets and Cisterns model" presents the extenuating circumstance to elucidate rice seed carotenoid metabolism.

Halogenated Diazabutadiene Dyes: Synthesis, Structures, Supramolecular Features, and Theoretical Studies.

Novel halogenated aromatic dichlorodiazadienes were prepared via copper-mediated oxidative coupling between the corresponding hydrazones and CCl4. These rare azo-dyes were characterized using 1H and 13C NMR techniques and X-ray diffraction analysis for five halogenated dichlorodiazadienes. Multiple non-covalent halogen···halogen interactions were detected in the solid state and studied by DFT calculations and topological analysis of the electron density distribution within the framework of Bader's theory (QTAIM method). Theoretical studies demonstrated that non-covalent halogen···halogen interactions play crucial role in self-assembly of highly polarizable dichlorodiazadienes. Thus, halogen bonding can dictate a packing preference in the solid state for this class of dichloro-substituted heterodienes, which could be a convenient tool for a fine tuning of the properties of this novel class of dyes.

Inverse Electron Demand Diels-Alder Reactions of Heterocyclic Azadienes, 1-Aza-1,3-Butadienes, Cyclopropenone Ketals, and Related Systems. A Retrospective.

A summary of the investigation and applications of the inverse electron demand Diels-Alder reaction is provided that have been conducted in our laboratory over a period that now spans more than 35 years. The work, which continues to provide solutions to complex synthetic challenges, is presented in the context of more than 70 natural product total syntheses in which the reactions served as a key strategic step in the approach. The studies include the development and use of the cycloaddition reactions of heterocyclic azadienes (1,2,4,5-tetrazines; 1,2,4-, 1,3,5-, and 1,2,3-triazines; 1,2-diazines; and 1,3,4-oxadiazoles), 1-aza-1,3-butadienes, α-pyrones, and cyclopropenone ketals. Their applications illustrate the power of the methodology, often provided concise and nonobvious total syntheses of the targeted natural products, typically were extended to the synthesis of analogues that contain deep-seated structural changes in more comprehensive studies to explore or optimize their biological properties, and highlight a wealth of opportunities not yet tapped.

Fluorine-19 magnetic resonance imaging probe for the detection of tau pathology in female rTg4510 mice.

Aggregation of tau into neurofibrillary tangles (NFTs) is characteristic of tauopathies, including Alzheimer's disease. Recent advances in tau imaging have attracted much attention because of its potential contributions to early diagnosis and monitoring of disease progress. Fluorine-19 magnetic resonance imaging (19 F-MRI) may be extremely useful for tau imaging once a high-quality probe has been formulated. In this investigation, a novel fluorine-19-labeling compound has been developed as a probe for tau imaging using 19 F-MRI. This compound is a buta-1,3-diene derivative with a polyethylene glycol side chain bearing a CF3 group and is known as Shiga-X35. Female rTg4510 mice (a mouse model of tauopathy) and wild-type mice were intravenously injected with Shiga-X35, and magnetic resonance imaging of each mouse's head was conducted in a 7.0-T horizontal-bore magnetic resonance scanner. The 19 F-MRI in rTg4510 mice showed an intense signal in the forebrain region. Analysis of the signal intensity in the forebrain region revealed a significant accumulation of fluorine-19 magnetic resonance signal in the rTg4510 mice compared with the wild-type mice. Histological analysis showed fluorescent signals of Shiga-X35 binding to the NFTs in the brain sections of rTg4510 mice. Data collected as part of this investigation indicate that 19 F-MRI using Shiga-X35 could be a promising tool to evaluate tau pathology in the brain.

Metabolic engineering of Methylobacterium extorquens AM1 for the production of butadiene precursor.

BACKGROUND: Butadiene is a platform chemical used as an industrial feedstock for the manufacture of automobile tires, synthetic resins, latex and engineering plastics. Currently, butadiene is predominantly synthesized as a byproduct of ethylene production from non-renewable petroleum resources. Although the idea of biological synthesis of butadiene from sugars has been discussed in the literature, success for that goal has so far not been reported. As a model system for methanol assimilation, Methylobacterium extorquens AM1 can produce several unique metabolic intermediates for the production of value-added chemicals, including crotonyl-CoA as a potential precursor for butadiene synthesis. RESULTS: In this work, we focused on constructing a metabolic pathway to convert crotonyl-CoA into crotyl diphosphate, a direct precursor of butadiene. The engineered pathway consists of three identified enzymes, a hydroxyethylthiazole kinase (THK) from Escherichia coli, an isopentenyl phosphate kinase (IPK) from Methanothermobacter thermautotrophicus and an aldehyde/alcohol dehydrogenase (ADHE2) from Clostridium acetobutylicum. The Km and kcat of THK, IPK and ADHE2 were determined as 8.35 mM and 1.24 s-1, 1.28 mM and 153.14 s-1, and 2.34 mM and 1.15 s-1 towards crotonol, crotyl monophosphate and crotonyl-CoA, respectively. Then, the activity of one of rate-limiting enzymes, THK, was optimized by random mutagenesis coupled with a developed high-throughput screening colorimetric assay. The resulting variant (THKM82V) isolated from over 3000 colonies showed 8.6-fold higher activity than wild-type, which helped increase the titer of crotyl diphosphate to 0.76 mM, corresponding to a 7.6% conversion from crotonol in the one-pot in vitro reaction. Overexpression of native ADHE2, IPK with THKM82V under a strong promoter mxaF in M. extorquens AM1 did not produce crotyl diphosphate from crotonyl-CoA, but the engineered strain did generate 0.60 µg/mL of intracellular crotyl diphosphate from exogenously supplied crotonol at mid-exponential phase. CONCLUSIONS: These results represent the first step in producing a butadiene precursor in recombinant M. extorquens AM1. It not only demonstrates the feasibility of converting crotonol to key intermediates for butadiene biosynthesis, it also suggests future directions for improving catalytic efficiency of aldehyde/alcohol dehydrogenase to produce butadiene precursor from methanol.

Extremely High Glass Transition Temperature Hydrocarbon Polymers Prepared through Cationic Cyclization of Highly 3,4-Regulated Poly(Phenyl-1,3-Butadiene).

A simple approach to synthesize extremely high glass transition temperature (Tg > 300 °C) hydrocarbon polymers that introduces bridged cyclic backbone and bulky pendant group simultaneously is reported. This method uses highly 3,4-regulated poly(phenyl-1,3-butadiene) as a prepolymer for cationic cyclization postmodification. The Tg of cyclized highly 3,4-regulated (94.0%) poly(1-phenyl-1,3-butadiene) (P(1-PB)) can reach 304 °C. To further restrict the movement of bridged cyclic backbone by changing the position of the pendant substituent group, highly 3,4-regulated (96.2%) poly(2-phenyl-1,3-butadiene) (P(2-PB)) is used as the prepolymer. The Tg of its cyclized product reaches 325 °C, and this value is the highest ever reported among all hydrocarbon polymers. The results indicate that the regularity of poly(phenyl-1,3-butadiene) and the pendant substituent group are crucial factors when synthesizing high-temperature hydrocarbon polymers through this approach.

Core-Shell Double Gyroid Structure Formed by Linear ABC Terpolymer Thin Films.

The synthesis and self-assembly in thin-film configuration of linear ABC triblock terpolymer chains consisting of polystyrene (PS), poly(2-vinylpyridine) (P2VP), and polyisoprene (PI) are described. For that purpose, a hydroxyl-terminated PS-b-P2VP (45 kg mol-1 ) building block and a carboxyl-terminated PI (9 kg mol-1 ) are first separately prepared by anionic polymerization, and then are coupled via a Steglich esterification reaction. This quantitative and metal-free catalyst synthesis route reveals to be very interesting since functionalization and purification steps are straightforward, and well-defined terpolymers are produced. A solvent vapor annealing (SVA) process is used to promote the self-assembly of frustrated PS-b-P2VP-b-PI chains into a thin-film core-shell double gyroid (Q230 , space group: Ia3¯d) structure. As terraces are formed within PS-b-P2VP-b-PI thin films during the SVA process under a CHCl3 vapor, different plane orientations of the Q230 structure ((211), (110), (111), and (100)) are observed at the polymer-air interface depending on the film thickness.

Synthesis and antioxidant, antixanthine oxidase, and antielastase activities of novel N,S-substituted polyhalogenated nitrobutadiene derivatives.

In this study, three substituted polyhalogenated nitrobutadiene derivatives were synthesized. Compound 1-[(2,3-dibromopropyl)sulfanyl]-1,3,4,4-tetrachloro-2-nitrobuta-1,3-diene (4) was synthesized before by our group. Compounds 8-{[1-[(2,3-dibromopropyl)sulfany]-3,4,4-trichloro-2-nitrobuta-1,3-butadien-1-yl}-1,4-dioxa-8-azaspiro[4.5]decane (5) and 1-[(2,3-dibromopropyl)sulfanyl]-3,4,4-trichloro-N-(4-methylpiperazin-1-yl)-2-nitrobuta-1,3-diene-1-amine (6) were synthesized in this work as original compounds. Xanthine oxidase, elastase inhibition abilities, and antioxidant activities were investigated in this work for compounds 4, 5, and 6. In this study, compounds 4, 5, and 6 exhibited antixanthine oxidase, antielastase, and antioxidant activities. Among the compounds screened, compound 4 exhibited xanthine oxidase and elastase inhibitor effect similar to the standard compound. Among the three tested compounds, compound 6 showed potent DPPH radical scavenging and reducing power activities. Therefore, these three compounds (4, 5, and 6) may be useful as an antixanthine oxidase, antielastase, and antioxidant agent in pharmaceutical and cosmetic industry.

The synthesis and evaluation of new butadiene derivatives as tubulin polymerization inhibitors.

A series of new butadiene derivatives was synthesized and evaluated as tubulin polymerization inhibitors for the treatment of cancer. The optimal butadiene derivative, 9a, exhibited IC50 values of 0.056-0.089µM for five human cancer cell lines. This paper included a mechanistic study of the antiproliferative activity, including a tubulin polymerization assay, an examination of morphological alterations of cancer cells, an analysis of cell cycle arrest and an apoptosis assay.

Bioinspired Design of a Robust Elastomer with Adaptive Recovery via Triazolinedione Click Chemistry.

It is a significant but challenging task to simultaneously reinforce and functionalize diene rubbers. Inspired by "sacrificial bonds", the authors engineer sacrificial hydrogen bonds formed by pendent urazole groups in crosslinked solution-polymerized styrene butadiene rubber (SSBR) via triazolinedione click chemistry. This post-crosslinking modification reveals the effects of the sacrificial bonds based on a consistent covalent network. The "cage effect" of the pre-crosslinked network facilitates the heterogeneous distribution of urazole groups, leading to the formation of hydrogen-bonded multiplets. These multiplets further aggregate into clusters with vicinal trapped polymer segments that form microphase separation from the SSBR matrix with a low content of urazole groups. The clusters based on hydrogen bonds, serving as sacrificial bonds, promote energy dissipation, significantly improving the mechanical properties of the modified SSBR, and enable an additional wide transition temperature region above room temperature, which endows the modified SSBR with promising triple-shape memory behavior.

Revisiting the concept of the (a)synchronicity of Diels-Alder reactions based on the dynamics of quasiclassical trajectories.

A number of model Diels-Alder (D-A) cycloaddition reactions (H2C=CH2 + cyclopentadiene and H2C=CHX + 1,3-butadiene, with X = H, F, CH3, OH, CN, NH2, and NO) were studied by static (transition state - TS and IRC) and dynamics (quasiclassical trajectories) approaches to establish the (a)synchronous character of the concerted mechanism. The use of static criteria, such as the asymmetry of the TS geometry, for classifying and quantifying the (a)synchronicity of the concerted D-A reaction mechanism is shown to be severely limited and to provide contradictory results and conclusions when compared to the dynamics approach. The time elapsed between the events is shown to be a more reliable and unbiased criterion and all the studied D-A reactions, except for the case of H2C=CHNO, are classified as synchronous, despite the gradual and quite distinct degrees of (a)symmetry of the TS structures.

α-Allenyl Ethers as Starting Materials for Palladium Catalyzed Suzuki-Miyaura Couplings of Allenylphosphine Oxides with Arylboronic Acids.

We disclose here the first palladium-catalyzed Suzuki-Miyaura couplings of aryl ethers functionalized allenylphosphine oxides with arylboronic acids. This new methodology with α-allenyl ethers as starting materials provides a novel approach to generate phosphinoyl 1,3-butadienes and derivatives with medium to excellent yields. The reaction tolerates a variety of functional groups to afford ranges of structurally diverse substituted phosphionyl 1,3-butadienes. For unsymmetrical allene substrates, high stereospecific additions to give E-isomers are usually observed. On the basis of the known palladium and allene chemistry, a mechanism is proposed.

Pd-carbene migratory insertion: application to the synthesis of trifluoromethylated alkenes and dienes.

Pd-catalyzed cross-coupling of halides with CF3-substituted diazo compounds or N-tosylhydrazones has been explored for the synthesis of CF3-substituted alkenes and 1,3-butadienes. Pd-carbene migratory insertion plays the key role in these transformations.

Synthesis of densely substituted 1,3-butadienes through acid-catalyzed alkenylations of α-oxoketene dithioacetals with aldehydes.

Aldehydes were proved to be viable reagents for implementing alkenylation of α-oxoketene dithioacetals. AlCl3 was found to be the best catalyst. The established reaction opened an avenue to access densely substituted 1,3-butadiene derivatives. The obtained product bears multiple reactive sites that can be converted into various valuable molecules.

Palladium-catalyzed 1,4-difunctionalization of butadiene to form skipped polyenes.

A palladium-catalyzed 1,4-addition across the commodity chemical 1,3-butadiene to afford skipped polyene products is reported. Through a palladium σ → π → σ allyl isomerization, two new carbon-carbon bonds are formed with high regioselectivity and trans stereoselectivity of the newly formed alkene. The utility of this method is highlighted by the successful synthesis of the ripostatin A skipped triene core.

Bicycle pedal photoisomerization of 1-phenyl-4-(4-pyridyl)-1,3-butadienes in glassy isopentane at 77 K.

In glassy isopentane at 77 K, 1-phenyl-4-(4-pyridyl)-cis-1,cis-3-butadiene (cc-PPyB) and 1-phenyl-4-(4-pyridyl)-cis-1,trans-3-butadiene (ct-PPyB) can undergo simultaneous two-bond photoisomerization. Under the same conditions, 1-phenyl-4-(4-pyridyl)-trans-1,cis-3-butadiene (tc-PPyB) gives tt-PPyB, the ultimate photoproduct in all cases.

Rhodium(III)-catalyzed oxidative olefination of N-allyl sulfonamides.

Rhodium(III)-catalyzed oxidative couplings between N-sulfonyl allylamines and activated olefins have been achieved. Only olefination occurred for acrylates, and the butadiene product can be further cyclized under palladium-catalyzed aerobic conditions. The coupling with N,N-dimethylacrylamide followed a cyclization pathway.