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Copper‐Catalyzed α,β‐Regioselective (2+4) Cycloaddition of Propargylic Esters
A copper-catalyzed α,β-regioselective (2+4) cycloaddition of propargylic esters with o-hydroxyphenyl substituted secondary phosphine oxides (SPOs) was established, which afforded a series of phosphorus-containing six-membered heterocycles in high yields (up to 99 % yield). This reaction represents the first α,β-regioselective (2+n) cycloaddition of propargylic esters via the intermediates of copper−allenylidenes, which will enrich the chemistry of propargylic esters and copper−allenylidenes. Moreover, this work also represents the first application of o-hydroxyphenyl substituted SPOs as 1,4-dinucleophiles in (2+4) cycloadditions, which provides a useful protocol for the synthesis of phosphorus-containing six-membered heterocycles with potential bioactivity.
One‐Pot Synthesis of Fused Tetrahydroquinoline‐Iminosugar Derivatives
An efficient and simple one-pot synthesis of structurally diverse novel tetrahydroquinolin fused iminosugars was developed through the aza-Diels-Alder mechanism. The adaptability of this method has been demonstrated by a variety of imines and D/L-ribose tosylates, and both electron-donating and withdrawing substituted imines are employed in reaction well. In addition, this reaction is characterized by simple operation, good yield, and high atom economy. Some synthetic iminosugars showed moderate anti proliferation of HCT116 tumor cells.
Efficient Synthesis of Fully Substituted and Diversely Functionalized Pyrazoles through p‐TSA Catalyzed One‐Pot Condensation of Cyclic β‐Diketones, Arylglyoxals and Arylhydrazones
An acid catalyzed one-pot condensation of readily available cyclic β-diketones, arylglyoxals and arylhydrazones produces a library of diversely functionalized pyrazole derivatives in excellent yield under metal-catalyst-free benign conditions.
Abstract
A one-pot, three-component, and atom economic synthesis of biologically and pharmaceutically important fully substituted and functionalized pyrazole derivatives has been accomplished under metal-catalyst-free benign conditions. The strategy involves early condensation of readily available cyclic β-diketones (dimidone, 4-hydroxycoumarin and 2-hydroxy-1,4-naphthoquinone) and arylglyoxals to generate a chalcone type intermediate which upon acid catalyzed condensation with ambident nucleophile arylhydrazones produces various aryl and cyclic β-diketone substituted pyrazole derivatives. The synthesis embraces high functional group tolerance, broad substrate scope, excellent yield of the products, short reaction time and operationally simple and mild reaction conditions. The synthesis provides an easy opportunity of incorporating biologically important N-diarylsulfide/selenide functionality, various enolisable cyclic β-diketones and other bioactive heterocycles concurrently to pyrazole, which may help in designing and development of pyrazole derivatives of pharmacological significance.
Using a Bayesian network model to predict effects of pesticides on aquatic community endpoints in a rice field – A southern European case study
Abstract
Bayesian network (BN) models are increasingly used as tools to support probabilistic environmental risk assessments (ERA), as they can better account for uncertainty compared to the simpler approaches commonly used in traditional ERA. We used BNs as meta-models to link various sources of information in a probabilistic framework, to predict the risk of pesticides to aquatic communities under given scenarios. The research focused on rice fields surrounding a Spanish Natural Park Albufera, considering three selected pesticides: acetamiprid (insecticide), MCPA (herbicide), and azoxystrobin (fungicide). The developed BN linked the inputs and outputs of two pesticide models: a process-based exposure model (RICEWQ), and probabilistic effects model (PERPEST) using case-based reasoning with data from microcosm and mesocosm experiments. The model characterised risk at three levels in a hierarchy: biological endpoints (e.g., molluscs, zooplankton, insects, etc.), endpoint groups (plants, invertebrates, vertebrates, and community processes), and community. The pesticide risk to a biological endpoint was characterised as the probability of an effect for a given pesticide concentration interval. The risk to an endpoint group was calculated as the joint probability of effect on any of the endpoints in the group. Likewise, community-level risk was calculated as the joint probability of any of the endpoint groups being affected. This approach enabled comparison of risk to endpoint groups across different pesticide types. For example, in a scenario for year 2050, the predicted risk of the insecticide to the community (40% probability of effect) was dominated by the risk to invertebrates (36% risk). In contrast, herbicide-related risk to the community (63%) was resulting from risk to both plants (35%) and invertebrates (38%); the latter might here represent indirect effects of toxicity through the food chain. This novel approach combines the quantification of spatial variability of exposure with probabilistic risk prediction for different components of aquatic ecosystems.
Reconnaissance Survey of Organic Contaminants of Emerging Concern in the Kabul and Swat Rivers of Pakistan
Abstract
The Swat and Kabul Rivers of Northern Pakistan are within an important regional watershed that support river-based livelihoods and are impacted by untreated effluent discharges and municipal solid waste. Anecdotal evidence indicates that fish populations are decreasing in these rivers. One potential cause of poor aquatic health is pollution; therefore, we investigated the presence of Contaminants of Emerging Concern (CECs) in the river systems. Water samples were collected in the Kabul River (n=9) and Swat River (n=10) during high (summer 2018) and low (winter 2019) river flow seasons. Agrochemicals, pharmaceuticals, plasticizers, chemicals in personal care products, and hormones were quantified via liquid chromatography high resolution mass spectrometry. In the Swat River, caffeine (18 ng/L to 8452 ng/L), DEET (16 ng/L to 56 ng/L), and plasticizers (13 ng/L to 7379 ng/L) were detected at all sites during both seasons, while butachlor (16 ng/L to 98 ng/L) was detected only during high flow. In the Kabul River, caffeine (12 ng/L to 2081 ng/L) and several plasticizers (91 ng/L to 722 ng/L) were detected at all sites during both seasons, while DEET (up to 97 ng/L) was detected only during high flow. Pharmaceuticals (analgesics and nonsteroidal anti-inflammatory drugs) were quantified in both rivers (up to 823 ng/L) with detection frequencies from 70-100% and 0-78%, respectively during low flow. Intermittent-use and natural seasonal processes (increased runoff and dilution from rainfall and snowmelt) yielded higher agrochemical concentrations and lower concentrations of continuous-use compounds (e.g., caffeine) during high flow. This study provides the first insight into CEC concentrations in the Swat River, additional insight into the Kabul River stressors, and overall, contaminant risks to aquatic life.
Asymmetric Reduction of Cyclic Imines by Imine Reductase Enzyme in Non‐conventional Solvents
The first enantioselective reduction of 2-substituted cyclic imines to the corresponding amines (pyrrolidines, piperidines, and azepines) by imine reductases (IREDs) in non-conventional solvents is reported. The best results were obtained in a glycerol/phosphate buffer 1:1 mixture, in which heterocyclic amines were produced with full conversions (>99%), moderate to good yields (22-84%) and excellent S-enantioselectivities (up to >99% ee). Remarkably, the process can be performed at a 100 mM substrate loading which, for the model compound, means a concentration of 14.5 g/L. A fed-batch protocol was also developed for a convenient scale-up transformation and one millimol of substrate 1a was readily converted into 120 mg of enantiopure amine (S)-2a with a remarkable 80% overall yield. This aspect strongly contributes in making the process potentially attractive for large scale applications in terms of economic and environmental sustainability to a discrete number of substrates to produce enantiopure cyclic amines of high pharmaceutical interest.
Fluorescent Molecular Photoswitches for the Generation of All‐Optical Encryption Keys
Herein, we report on a tri-component photochromic molecular cocktail that can be used to encrypt and decrypt information. The time-dependent fluorescent response of this cocktail is highly non-linear with respect to the set of inputs used (concentrations of the three photochromic components, excitation- and emission wavelengths), a property required for the generation of so-called encryption keys. The all-optical system can generate more than 8 million unique fluorescence responses by applying different input combinations and is operated using a conventional fluorimeter.
A Cobalt nanocatalyst for the hydrogenation and oxidative dehydrogenation of N‐heterocycles
Catalytic hydrogenation and oxidative dehydrogenation of N-heterocycles to produce tetrahydroquinoline and quinoline derivatives are important reactions of particular importance in the agrochemical and pharmaceutical industries. Herein, we report earth-abundant cobalt nanoparticles supported on hydroxyapatite (HAP) as an inexpensive and efficient catalyst for the hydrogenation and reverse oxidative dehydrogenation of N-heterocycles. The optimal nanocatalyst exhibits excellent activity in both reactions for a wide range of substrates including (iso)quinolines, acridine, benzo[h]quinoline, quinoxaline and indole. Reactions proceed under relatively mild conditions without requiring any additives.
Towards Copper(I) Clusters for Photo‐ Induced Oxidation of Biological Thiols in Living Cells
The cell redox balance can be disrupted by the oxidation of biological peptides and eventually lead to the cell death, which provides opportunities to develop cytotoxic drugs. With the aim of developing compounds capable of specifically inducing fatal redox reactions upon irradiation, we have developed a library of copper compounds. This metal is abundant and considered essential for human health, making it particularly attractive for the development of new anticancer drugs. Copper(I) clusters with thiol ligands (including 5 novel ones) have been synthesized and characterized. Structures were elucidated by X-ray diffraction and show that the compounds are oligomeric clusters. The clusters display high photooxidation capacity towards cysteine – an essential amino acid – upon irradiation in the visible range (450 nm), while remaining completely inactive in the dark. This photoredox activity against a biological thiol was very encouraging for the development of an anticancer photoredox drug. Besides, the in vitro assay on murine colorectal cancer cells (CT26) did not show any toxicity – whether in the dark or when exposed to 450 nm light, likely because of the poor solubility of the complexes in biological medium.