A Simple Copper‐Catalyzed Cascade Synthesis of 2‐Amino‐1H‐indole‐3‐carboxylate Derivatives

We have developed a simple and efficient copper‐catalyzed method for the synthesis of 2‐amino‐1H‐indole‐3‐carboxylate derivatives via cascade reactions of substituted N‐(2‐halophenyl)‐2,2,2‐trifluoroacetamide with alkyl 2‐cyanoacetate or malononitrile under mild conditions, and the method is of wide practical application.     

Cytochrome c Catalyzes the Hydrogen Peroxide‐Assisted Oxidative Desulfuration of 2‐Thiouridines in Transfer RNAs

The 5‐substituted 2‐thiouridines (R5S2Us) present in the first (wobble) position of the anticodon of transfer RNAs (tRNAs) contribute to accuracy in reading mRNA codons and tuning protein synthesis. Previously, we showed that, under oxidative stress conditions in vitro, R5S2Us were sensitive to hydrogen peroxide (H₂O₂) and that their oxidative desulfuration produced 5‐substituted uridines (R5Us) and 4‐pyrimidinone nucleosides (R5H2Us) at a ratio that depended on the pH and an R5 substituent. Here, we demonstrate that the desulfuration of 2‐thiouridines, either alone or within an RNA/tRNA chain, is catalyzed by cytochrome c (cyt c). Its kinetics are similar to those of Fenton‐type catalytic 2‐thiouridine (S2U) desulfuration. Cyt c/H₂O₂‐ and Fe^II‐mediated reactions deliver predominantly 4‐pyrimidinone nucleoside (H2U)‐type products. The pathway of the cyt c/H₂O₂‐peroxidase‐mediated S2U→H2U transformation through uridine sulfenic (U‐SOH), sulfinic (U‐SO₂H), and sulfonic (U‐SO₃H) intermediates is confirmed by LC–MS. The cyt c/H₂O₂‐mediated oxidative damage of S2U‐tRNA may have biological relevance through alteration of the cellular functions of transfer RNA.     

Gold(I)‐Catalyzed Reactions of 1‐(ortho‐Alkynylaryl)ureas: Highly Selective Heterocyclization and Synthesis of Mixed N,O‐Acetals

Readily available 1‐(ortho‐ethynylaryl)urea derivatives undergo a selective gold/silver {[AuCl(IPr)]/AgSbF₆} catalyzed N‐6‐exo‐dig or N‐5‐endo‐dig heterocyclization process in dimethylformamide (DMF) at 60 °C. Benzoxazine derivatives, i.e., the products of O‐6‐exo‐dig ring closure through the urea oxygen, could be observed under catalytic conditions only when the N‐3 basicity was substantially diminished, but were readily isolable in stoichiometric processes carried out at low temperature. The open chain amino O,O‐acetals and a series of new cyclic mixed N,O‐acetals containing the trifluoroethyl group were synthesized when the reactions were performed in ethanol or trifluoroethanol, respectively, as solvent. The procedure allows for an easy access to this versatile class of key intermediates in organic synthesis from simple starting materials. The effect of using either DMF or protic solvents on the course of the reactions is reported.

     

Use of chitosan for removal of bisphenol A and bisphenol derivatives through tyrosinase‐catalyzed quinone oxidation

In this study, the availability of chitosan was systematically investigated for removal of bisphenol A (BPA, 2,2‐bis(hydroxyphenyl)propane) through the tyrosinase‐catalyzed quinone oxidation and subsequent quinone adsorption on chitosan beads. In particular, the process parameters, such as the hydrogen peroxide (H₂O₂)‐to‐BPA ratio, pH value, temperature, and tyrosinase dose, were discussed in detail for the enzymatic quinone oxidation. Tyrosinase‐catalyzed quinone oxidation of BPA was effectively enhanced by adding H₂O₂ and the optimum conditions for BPA at 0.3 mM were determined to be pH 7.0 and 40°C in the presence of H₂O₂ at 0.3 mM ([H₂O₂]/[BPA] = 1.0). Removal of BPA from aqueous solutions was accomplished by adsorption of enzymatically generated quinone derivatives on chitosan beads. The use of chitosan in the form of beads was found to be more effective because heterogeneous removal of BPA with chitosan beads was much faster than homogeneous removal of BPA with chitosan solutions, and the removal efficiency was enhanced by increasing the amount of chitosan beads dispersed in the BPA solutions and BPA was completely removed by quinone adsorption in the presence of chitosan beads more than 0.10 cm³/cm³. In addition, a variety of bisphenol derivatives were completely or effectively removed by the procedure constructed in this study, although the enzyme dose or the amount of chitosan beads was further increased as necessary for some of the bisphenol derivatives used. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Dye bleaching and phenol precipitation by phthalic anhydride‐modified horseradish peroxidase

The phenol precipitation and dye bleaching capabilities of phthalic anhydride–modified horseradish peroxidase C (PA–HRP) were compared with those of native HRP C and ethylene glycol‐ bis‐(succinic acid N‐hydroxysuccinimide ester)–modified HRP (EG–HRP) reported previously. Removal efficiency (percentage of phenol removed from solution under experimental conditions) was determined for native HRP and both modified forms. Removal efficiencies at 37 °C were very similar, with >95% removal in each case. Removal efficiencies were less at 70 °C overall (range 25–45%) but PA–and EG–HRP removed up to 50% more phenol than native HRP. The three HRP forms showed similar dye bleaching performance at 37 °C in the presence of H₂O₂ and accelerators (up to 86% colour removal). PA–and EG–HRP showed slightly greater bleaching abilities at 65 °C than native HRP for some of the dye/accelerator combinations tested. Modified HRPs performed better in 40% (v/v) mixtures of dioxane or dimethylformamide. © 2000 Society of Chemical Industry     

Horseradish peroxidase‐mediated in situ forming hydrogels from degradable tyramine‐based poly(amido amine)s

Horseradish peroxidase (HRP)‐mediated crosslinking of poly(amido amine) (PAA) copolymers was successfully applied in the preparation of in situ forming degradable hydrogels under physiological conditions. PAA copolymers containing different amounts of tyramine residues (termed as pAEEOL/TA) could be synthesized through Michael‐type addition between methylenebisacryamide and amine mixture of 2‐(2‐aminoethoxy) ethanol and tyramine (TA). Depending on the amount of TA residue, the HRP, and H₂O₂ concentration, the gelation times could be varied from about 50 to 350 s. The swelling and degradation experiments indicated under physiological conditions the pAEEOL/TA‐based hydrogels are completely degradable within 6–8 days. Rheological analysis revealed that storage modulus of the hydrogels increased from 2500 to 4100 Pa when increasing HRP concentrations. Importantly, pAEEOL/TA copolymers have low cytotoxicity. Moreover, NIH 3T3 (mouse embryonic fibroblast) cells exposed in the degradation products of pAEEOL/TA‐based hydrogels retained high cell viability, implying that the hydrogels are cyto‐biocompatible. In vitro release of methylene blue and IgG protein from pAEEOL/TA‐based hydrogels could be effectively sustained by encapsulation of the drug in the hydrogels. The results indicate that HRP‐crosslinked, degradable pAEEOL/TA‐based hydrogels are promising for biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Untersuchung der CO2‐Absorptionskinetik in wässrigen Lösungen von N,N‐Diethylethanolanmin und N‐Ethylethanolamin

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA and the liquid‐side mass transfer coefficient were determined from the absorption rate measurements in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor was applied for the absorption studies, whereas a zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics.     

Palladium on Carbon‐Catalyzed Cross‐Coupling using Triarylbismuths

Simple and efficient protocols for the 10% palladium on carbon (Pd/C)‐catalyzed cross‐coupling reactions between triarylbismuths and aryl halides have been developed. A variety of iodo‐ and bromobenzenes possessing an electron‐withdrawing group on the aromatic nucleus were smoothly cross‐coupled in the presence of 10% Pd/C, sodium phosphate dodecahydrate (Na₃PO₄⋅12 H₂O) and 1,4‐diazabicyclo[2.2.2]octane (DABCO) in heated N‐methyl‐2‐pyrrolidone (NMP) as the solvent. For the arylations of iodobenzenes, the reactions effectively proceeded under the combined use of caesium fluoride (CsF) and 2,2′‐biquinoline. Furthermore, a ligand‐free 10% Pd/C‐catalyzed cross‐coupling reaction between the aryl iodides and triarylbismuths was also established by the addition of tetra‐n‐buthylammonium fluoride trihydrate (TBAF⋅3 H₂O) in which the palladium metals were hardly leached from the catalyst into the reaction media.     

An Efficient Domino Synthesis of Quinoxalin‐2(1H)‐ones via an SNAr/Coupling/Demesylation Reaction Catalyzed by Copper(I) as Key Step

An efficient copper‐catalyzed method for the synthesis of quinoxalin‐2(1 H)‐ones derivatives via domino S_NAr/coupling/demesylation reaction of N‐(2‐halophenyl)methylsulfonamides with 2‐halo amides has been developed. Various quinoxalinones with diversity at three positions on their scaffold have been obained, and the method is valuable for the construction of this kind of molecules with biological and pharmaceutical activities.     

A novel hydrogen peroxide sensor based on Ag nanoparticles decorated polyaniline/graphene composites

A novel electrochemical sensor based on Ag nanoparticles (AgNPs) decorated polyaniline/graphene composites (PANI/G) is developed, which can be used for sensitive determination of H₂O₂. For the construction of the H₂O₂ sensor, polyaniline (PANI) is first electrodeposited on the surface of graphene (G) to form PANI/G, and then horseradish peroxidase (HRP) loaded on AgNPs (HRP/AgNPs) is immobilized on to the PANI/G. H₂O₂ can be catalyzed by HRP to generate current response which can be significantly enhanced by AgNPs, and thus the PANI/G based sensor can be utilized for the detection of H₂O₂. Under the optimized conditions, the proposed H₂O₂ sensor exhibits wide linear response to H₂O₂ concentration ranging from 0.25 to 2.25 mM with a detection limit of 0.03 mM (signal‐to‐noise ratio of 3), and it also shows high selectivity and reproducibility. The method is simple and cost‐effective, and can be a promising candidate as the sensitive sensing platform for H₂O₂. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42409.     

Bifunctional Catalysts Stabilized on Nanocrystalline Magnesium Oxide for One‐Pot Synthesis of Chiral Diols

New bifunctional catalysts composed of PdCl₄²⁻, OsO₄²⁻ and OsO₄²⁻, WO₄²⁻ designed and prepared by a counterionic stabilization technique involving the reactions of Na₂PdCl₄‐K₂OsO₄ and K₂OsO₄‐Na₂WO₄ with nanocrystalline MgO are well characterized. These bifunctional catalysts, NAP‐Mg‐PdOs and NAP‐Mg‐OsW perform tandem Heck asymmetric dihydroxylation and asymmetric dihydroxylation‐N‐oxidation reactions, respectively, in the presence of the chiral ligand 1,4‐bis(9‐o‐dihydroquinidinyl)phthalazine [(DHQD)₂PHAL] in a single pot. It is quite impressive to note that H₂O₂ is used as a terminal oxidant to provide N‐methylmorpholine N‐oxide (NMO) in situ by the oxidation of N‐methylmorpholine (NMM) in the asymmetric dihydroxylation‐N‐oxidation catalyzed by NAP‐Mg‐OsW.     

Synthesis, σ Receptor Affinity,and Pharmacological Evaluation of 5‐Phenylsulfanyl‐ and 5‐Benzyl‐Substituted Tetrahydro‐2‐benzazepines

In accordance with a novel strategy for generating the 2‐benzazepine scaffold by connecting C6–C1 and C3–N building blocks, a set of 5‐phenylsulfanyl‐ and 5‐benzyl‐substituted tetrahydro‐2‐benzazepines was synthesized and pharmacologically evaluated. Key steps of the synthesis were the Heck reaction, the Stetter reaction, a reductive cyclization, and the introduction of diverse N substituents at the end of the synthesis. High σ₁ affinity was achieved for 2‐benzazepines with linear or branched alk(en)yl residues containing at least an n‐butyl substructure. The butyl‐ and 4‐fluorobenzyl‐substituted derivatives, (±)‐5‐benzyl‐2‐butyl‐2,3,4,5‐tetrahydro‐1H‐2‐benzazepine ( 19 b ) and (±)‐5‐benzyl‐2‐(4‐fluorobenzyl)‐2,3,4,5‐tetrahydro‐1H‐2‐benzazepine ( 19 m ), show high selectivity over more than 50 other relevant targets, including the σ₂ subtype and various binding sites of the N‐methyl‐D ‐aspartate (NMDA) receptor. In the Irwin screen, 19 b and 19 m showed clean profiles without inducing considerable side effects. Compounds 19 b and 19 m did not reveal significant analgesic and cognition‐enhancing activity. Compound 19 m did not have any antidepressant‐like effects in mice.     

Gas‐separation properties of amine‐crosslinked polyimide membranes modified by amine vapor

The modification of a polyimide (PI) membrane by aromatic amine vapor was performed in this work to increase the crosslinking of the membrane and to study the effect on gas permeability and the corresponding selectivity. The single‐gas permeability of the membranes at 35 °C was probed for H₂, O₂, N₂, CO₂, and CH₄. From the relationship between the combinations of gases and ideal permselectivities, this study showed that amine‐crosslinked PI membranes tended to increase gas permselectivities exponentially with the increasing difference in gas kinetic diameter. Moreover, this study illustrated that the permeability of the membranes was influenced by the formation rate of amine‐crosslinked networks or chemical structures after the reaction. The membranes had the highest level of permselectivities among crosslinked PI membranes for O₂/N₂, and the H₂/CH₄ permselectivity increased 26 times after vapor modification. Furthermore, the modification method that used aromatic amine vapor produced thin and strongly modified layers. These findings indicate that modification is an advantageous technique for improving gas‐separation performance, even considering thinning. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44569.     

Cinchona Alkaloid‐Catalyzed Enantioselective Direct Aldol Reaction of N‐Boc‐Oxindoles with Polymeric Ethyl Glyoxylate

The first enantioselective direct aldol addition of N‐Boc‐oxindoles to polymeric ethyl glyoxylate is presented. The reaction is performed by using as low as 0.1 mol% (DHQ)₂PHAL and gives access to α‐hydroxycarboxylate derivatives bearing adjacent secondary alcohol and quaternary stereocenters with high levels of diastereo‐ and enantiocontrol. The use of ethyl glyoxylate in its polymeric form represents an important advantage for synthetic applications and allows us to directly install a C₂ unit ready to be converted in useful building blocks. A further one‐pot protection/deprotection sequence catalyzed by Zn(ClO₄)₂⋅6 H₂O preserved the α‐hydroxycarboxylates from racemization by means of a parasitic alcohol‐catalyzed retroaldol reaction.     

Versatile Synthesis of Pyrrole‐2‐acetic Esters and (Pyridine‐2‐one)‐3‐acetic Amides by Palladium‐Catalyzed,Carbon Dioxide‐Promoted Oxidative Carbonylation of (Z)‐(2‐En‐4‐ynyl)amines

The oxidative carbonylation of readily available (Z)‐(2‐en‐4‐ynyl)amines, catalyzed by the PdI₂‐KI system, selectively afforded in satisfactory yields (40–95 %) either pyrrole‐2‐acetic ester or (pyridine‐2‐one)‐3‐acetic amide derivatives, depending on the susbtitution pattern of the substrate and the reaction conditions. The presence of an excess of carbon dioxide proved in most cases to be beneficial to both the reaction rate and product selectivity.     

Synthesis of α‐Carbolines Starting from 2,3‐Dichloropyridines and Substituted Anilines

9H‐α‐Carbolines have been prepared via consecutive intermolecular Buchwald–Hartwig reaction and Pd‐catalyzed intramolecular direct arylation from commercially available 2,3‐dichloropyridines and substituted anilines. The combination of a high reaction temperature (180 °C) and the use of DBU were found to be crucial for the intramolecular direct arylation reactions of the 3‐chloro‐N‐phenylpyridin‐2‐amines as no reaction was observed at 120 °C and 180 °C using different inorganic and other organic bases. On the other hand, nitrogen‐methylated pyridine analogues of these substrates {N‐[3‐chloro‐1‐methylpyridin‐2(1H)‐ylidene]anilines} do undergo ring closure at 120 °C, with K₃PO₄ as base, affording the respective 1‐methyl‐1H‐α‐carbolines in good yields.     

Synthesis and Cytostatic and Antiviral Activities of 2′‐Deoxy‐2′,2′‐difluororibo‐ and 2′‐Deoxy‐2′‐fluororibonucleosides Derived from 7‐(Het)aryl‐7‐deazaadenines

A series of sugar‐modified derivatives of cytostatic 7‐heteroaryl‐7‐deazaadenosines (2′‐deoxy‐2′‐fluororibo‐ and 2′‐deoxy‐2′,2′‐difluororibonucleosides) bearing an aryl or heteroaryl group at position 7 was prepared and screened for biological activity. The difluororibonucleosides were prepared by non‐ stereoselective glycosidation of 6‐chloro‐7‐deazapurine with benzoyl‐protected 2‐deoxy‐2,2‐difluoro‐D ‐erythro‐pentofuranosyl‐1‐mesylate, followed by amination and aqueous Suzuki cross‐couplings with (het)arylboronic acids. The fluororibo derivatives were prepared by aqueous palladium‐catalyzed cross‐coupling reactions of the corresponding 7‐iodo‐7‐deazaadenine 2′‐deoxy‐2′‐fluororibonucleoside 20 with (het)arylboronic acids. The key intermediate 20 was prepared by a six‐step sequence from the corresponding arabinonucleoside by selective protection of 3′‐ and 5′‐hydroxy groups with acid‐labile groups, followed by stereoselective S_N2 fluorination and deprotection. Some of the title nucleosides and 7‐iodo‐7‐deazaadenine intermediates showed micromolar cytostatic or anti‐HCV activity. The most active were 7‐iodo and 7‐ethynyl derivatives. The corresponding 2′‐deoxy‐2′,2′‐difluororibonucleoside 5′‐O‐triphosphates were found to be good substrates for bacterial DNA polymerases, but are inhibitors of human polymerase α.     

Efficient Synthesis of 9‐Tosylaminofluorene Derivatives by Boron Trifluoride Etherate‐Catalyzed Aza‐Friedel–Crafts Reaction of in situ Generated N‐Tosylbenzaldimines

An efficient and expeditious boron trifluoride etherate (BF₃⋅Et₂O) catalyzed one‐pot reaction for the synthesis of N‐tosyl‐9‐aminofluorenes and anthracene derivatives from in situ generated N‐tosylbenzaldimines via an aza‐Friedal–Crafts reaction has been developed. The catalytic reaction shows high substrate tolerance with excellent yields.     

Synthesis of Difurylmethane Derivatives via the Gold‐Catalyzed Tandem Cycloisomerization/Dimerization of Epoxide Alkynes

A simple and convenient synthetic approach to difurylmethane derivatives has been developed via gold‐catalyzed cycloisomerization of 1‐oxiranyl‐2‐alkynyl esters and dimerization of the 2‐(α‐hydroxyalkyl)furans. The reaction takes place in the presence of 2 mol% of tetrachloroauric acid tetrahydrate (HAuCl₄⋅4 H₂O) under very mild conditions.     

Effects of crosslinking modification on the O2/N2 separation characteristics of poly(phenyl sulfone)/poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) blend membranes

A series of blend membranes of poly(phenyl sulfone) (PPSU) with poly(bisphenol A‐co‐4‐nitrophthalic anhydride‐co‐1,3‐phenylenediamine) (PBNPI) were prepared through a solution casting method. This was done to examine the permeation characteristics of oxygen and nitrogen. The effect of the PPSU/PBNPI ratio on the membrane structure and O₂/N₂ separation performance were investigated. The results show that the permeability increased remarkably with the content of PPSU, whereas the selectivity decreased slightly. To enhance the selectivity of O₂/N₂, the blend membranes were further crosslinked with a p‐xylylenediamine agent via the immersion method. According to the Fourier transform infrared analysis, the N? H group was formed on the imide group of PBNPI. Therefore, we suggest that during the crosslinking modification, the PBNPI served as a crosslinkable polymer; this resulted in increased crosslinking efficiency with PBNPI content. The high‐resolution X‐ray diffraction and melting point method results show that crosslinking modification improved the selectivity with an acceptable loss in permeability along with increased crystallinity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010