Rh(III)-Catalyzed C7-Alkylation of Isatogens with Malonic Acid Diazoesters.

Rh(III)-catalyzed C7-alkylation of isatogens (indolin-3-one N-oxides) with malonic acid diazoesters has been developed. This strategy utilizes oxygen anion on the N-oxide group of isatogens as a directing group and successfully achieves the synthesis of a series of C7-alkylated isatogens with moderate to good yields (48-86% yields). Moreover, the N-oxides of isatogens can not only serve as the simple directing group for C7-H bond cleavage but also be deoxidized for easy removal.

Aerobic Dehydrogenative Aromatization in the Preparation of 4-Aminoquinoline Derivatives by Synergistic Pd/Cu Catalysis.

The 4-aminoquinoline moiety is widely present in various bioactive compounds and marketed drugs, while the preparation of this target structure relies heavily on the amination of 4-chloroquinolines. Herein, an atom and step economic procedure was developed based on an aerobic dehydrogenative aromatization strategy. Unlike the well-known palladium-catalyzed dehydrogenative aromatization of cyclohexanones with amines, synergistic Pd/Cu catalysis is crucial for 2,3-dihydroquinolin-4(1H)-one type of substrates. Under the optimized conditions, a range of aromatic/aliphatic amines and 2,3-dihydroquinolin-4(1H)-ones were coupled to give the corresponding 4-aminoquinoline products in moderate to high yields, and the application of the current methodology for the preparation and late-stage diversification of marketed drugs was also demonstrated.

A New Fluorescent Probe for Hydrogen Sulfide Detection in Solution and Living Cells.

Since Hydrogen Sulfide (H2S) was recognized as a gas transmitter, its detection and quantification have become a hot research topic among chemists and biologists. In this area, fluorescent probes have shown great advantages: fast and strong response, low detection limit and easy manipulation. Here we developed a new fluorescent probe that detected H2S selectively among various bioactive and inorganic salts. This probe was based on the core structure of fluorescein and reacted with H2S through azide-reduction. Great linearity was achieved correlating fluorescence intensity and H2S concentrations in solution. The detection of H2S in cancer cells was also achieved.

Synthesis of N-Unsubstituted and N3-Substituted Quinazoline-2,4(1H,3H)-diones from o-Aminobenzamides and CO2 at Atmospheric Pressure and Room Temperature.

The unprecedented metal-free synthesis of both N-unsubstituted and N3-substituted quinazoline-2,4(1H,3H)-diones from o-aminobenzamides and CO2 under atmospheric pressure at room temperature is developed. This protocol easily allows for variations of functional groups (including alkyl, aryl, and heterocycle groups) at the N3-position to accommodate the construction of many important drugs and bioactive compounds. The reaction features eco-friendliness, substrate scope tolerance, and versatility and can be implemented even at the gram scale.

Protecting-Group-Free Synthesis of Meridianin A-G and Derivatives and Its Antibiofilm Evaluation.

Herein, a protecting-group-free protocol was developed to realize a time and step economy diversification of the Meridianin alkaloid. A broad range of substituents are tolerated to deliver the products in moderate to high yields, and the first synthesis of Meridianin B was achieved. The simplicity of this protocol enables the rapid construction of a Meridianin derivative library for antibiofilm evaluation. Preliminary results reveal that Meridianin derivatives were capable of inhibiting the Acinetobacter baumannii biofilm and lowering the antibiotic MIC synergistically.

DBU-Catalyzed Aerobic CDC Reaction of Thiophenols.

A convenient method was developed for the preparation of thiolated compounds via a DBU-catalyzed aerobic cross-dehydrogenative coupling (CDC) reaction. The established protocol is environmentally friendly and operationally simple. Substrates like (hetero)aryl acetates, (hetero)aryl ketones, and indoles could be transformed into the corresponding thiolated products in moderate to high yields and further applied in the preparation of bioactive compounds in a prefunctionalization-free manner.

Synthesis and antibiofilm evaluation of N-acyl-2-aminopyrimidine derivatives against Acinetobacter baumannii.

The overuse of antibiotics will led to the increase of drug resistance. Especially, the multidrug-resistant A. baumannii became the leading cause of nosocomial infections with high rates of morbimortality. The drug resistance of A. baumannii is greatly attributed to its biofilm. To alleviate the burden of drug resistance, the anti-virulence signaling strategies was developed. By specifically interfering with the ability of the bacteria to recognize host signals that are needed to establish infection, the bacteria are less able to colonize the host. In this paper, 39 N-acyl-2-aminopyrimidine derivatives were synthesized and tested for their biofilm inhibition efficacy. The screening results reveal that some of the analogues (3ac, 8d) efficiently inhibited the biofilm formation of A. baumannii (IC50 as low as 3.8 µM), and the biofilm inhibition ability was further demonstrated with laser confocal results and extracellular polysaccharides inhibition test. Further motility test reveals our compounds are quorum sensing inhibitors. Besides, the synergistic effect of compounds 3ac and 8d with different antibiotics suggest its potential clinical significance, which was further enhanced by the long time biofilm inhibition test after coating with PLGA. Finally, we also look into the safety of the compounds with cytotoxicity assay.

Synthesis and antibacterial activity studies in vitro of indirubin-3'-monoximes.

Multi-drug-resistant microbial pathogens are a serious global health problem. New compounds with antibacterial activity serve as good candidates for developing novel antibacterial drugs which is very urgent and important. In this work, based on the unique scaffold of indirubin, an active ingredient of traditional Chinese medicine formulation Danggui Luhui Wan, we synthesized 29 indirubin-3'-monoximes and preliminarily evaluated their antibacterial activities. The antibacterial activity results demonstrated that the synthesized indirubin-3'-monoximes 5a-5z and 5aa-5ad displayed good potency against S. aureus ATCC25923 (MIC = 0.4-25.6 µg mL-1). Among them, we found that the 5-F, 5-Cl and 7-CF3 substituted indirubin-3'-monoximes 5r, 5s and 5aa also showed better antibacterial efficiency for S. aureus (MICs up to 0.4 µg mL-1) than the prototype natural product indirubin (MIC = 32 µg mL-1). More importantly, indirubin-3'-monoxime 5aa has certain synergistic effect with levofloxacin against clinic multidrug-resistant S. aureus (fractional inhibitory concentration index: 0.375). In addition, relevant experiments including electron microscopy observations, PI staining and the leakage of extracellular potassium ions and nucleic acid (260 nm) have been performed after treating S. aureus with indirubin-3'-monoxime 5aa, and the results revealed that indirubin-3'-monoximes could increase the cell membrane permeability of S. aureus. Although indirubin-3'-monoxime 5aa showed some cytotoxicity toward SH-SY5Y cells relative to compounds 5r and 5s, the skin irritation test of male mice after shaving showed that compound 5aa at a concentration of 12.8 µg mL-1 had no toxicity to mouse skin, and it could be used as a leading compound for skin antibacterial drugs.

Cobalt-promoted synthesis of sulfurated oxindoles via radical annulation of N-arylacrylamides with disulfides.

An efficient radical annulation of N-arylacrylamides with disulfides is developed for the synthesis of sulfurated oxindoles. The reaction occurs in a facile manner using CoBr2 as both an initiator and a promoter for the first time and (NH4)2S2O8 as the oxidant. By controlling the CoBr2/(NH4)2S2O8 ratio, a wide range of sulfurated and brominated/sulfurated oxindoles are selectively prepared in good to excellent yields. The present protocol is simple and highly atom economical, and can tolerate a broad range of substrates.

Cinchona-Alkaloid-Derived NNP Ligand for Iridium-Catalyzed Asymmetric Hydrogenation of Ketones.

Most ligands applied for asymmetric hydrogenation are synthesized via multistep reactions with expensive chemical reagents. Herein, a series of novel and easily accessed cinchona-alkaloid-based NNP ligands have been developed in two steps. By combining [Ir(COD)Cl]2, 39 ketones including aromatic, heteroaryl, and alkyl ketones have been hydrogenated, all affording valuable chiral alcohols with 96.0-99.9% ee. A plausible reaction mechanism was discussed by NMR, HRMS, and DFT, and an activating model involving trihydride was verified.

Iron-Catalyzed Radical Annulation of Unsaturated Carboxylic Acids with Disulfides for the Synthesis of γ-Lactones.

An efficient aerobic iron-catalyzed annulation of unsaturated carboxylic acids with disulfides has been developed. This procedure proceeds using FeCl3 as the catalyst and KI as an iodine source under an air atmosphere, which provides practical access to a wide range of substituted γ-lactone derivatives. The disclosed method is quite simple, highly atom-economic, environmentally friendly, and tolerates a broad substrate scope.

Synthesis and antibiofilm evaluation of 3-hydroxy-2,3-dihydroquinazolin-4(1H)-one derivatives against opportunistic pathogen Acinetobacter baumannii.

The emergence of multidrug resistant microorganisms has triggered the impending need for new aitimicrobial strategies. The antivirulence strategy with the benefite of alleviating the drug resistance becomes the focus of research. In this study, 22 quorum sensing inhibitors were synthesized by mimicking the structure of autoinducer and acinetobactin and up to 34% biofilm inhibition was observed with 5u. The biofilm inhibition effect was further demonstrated with extracellular polysaccharides inhibition and synergism with Gentamycin sulphate.

Palladium catalyzed asymmetric allylic alkylation of isoquinolinedione derivatives in the preparation of quaternary carbon stereocenters.

A highly enantioselective allylic alkylation of isoquinolinedione derivatives under palladium catalysis was developed in the preparation of quaternary carbon stereocenters. Under standard reaction conditions, excellent yields and enantioselectivities were realized and the products could be transformed into dihydroisoquinolone with vicinal chiral carbon centers or THIQ core structures in short steps with high yields.

Enantioselective amination of 4-alkylisoquinoline-1,3(2H,4H)-dione derivatives.

A mild and efficient enantioselective amination of 4-alkylisoquinoline-1,3(2H,4H)-dione derivatives was established, which is compatible with a broad range of substrates and delivers the final products in excellent yields (up to 99%) and ee values (up to 99%) with low catalyst loading (down to 1 mol%). The synthetic potential of this methodology was also demonstrated in the gram scale level.

Organocatalytic Asymmetric α-Sulfenylation of 2-Substituted Indolin-3-ones: A Strategy for the Synthesis of Chiral 2,2-Disubstituted Indole-3-ones with S- and N-Containing Heteroquaternary Carbon Stereocenter.

An organocatalytic asymmetric α-sulfenylation of 2-substituted indolin-3-ones with N-(alkylthio or arylthio)succinimides has been developed for the first time using Cinchona-derived squaramide as the catalyst. Various chiral 2,2-disubstituted indole-3-ones with S- and N-containing heteroquaternary carbon stereocenters were obtained with up to 98% yield and 99% ee.

Catalyst-free Cleavage of Amide and C-O Double Bond for the Diastereoselective Synthesis of Trifluoromethyl-Containing Dihydrooxazole Derivatives.

A novel and efficient cascade method has been developed for the diastereoselective preparation of trifluoromethyl-containing dihydrooxazoles in high yields. The reaction was applicable to electron-deficient, electron-rich arenes, heteroarenes, and alkyl groups. Control experiments were conducted to explore the reaction mechanism and reveal that the byproduct formed in situ is the catalyst for this reaction and a tether derived from trifluoropyruvate is a key intermediate for this reaction.

Reductant-Free Aerobic Hydroxylation of Isoquinoline-1,3(2 H,4 H)-dione Derivatives.

Base-catalyzed efficient hydroxylation of isoquinoline-1,3(2 H,4 H)-diones with air under transition-metal-free and reductant-free conditions was established. This methodology is essentially mild and compatible with a broad range of substrates, including aryl, heteroaryl, and alkyl groups. Also, the product could be simply transformed into a hydroxylated tetrahydroisoquinoline core structure through a reductive process.

Synthesis of 4-Aryl Isoquinolinedione Derivatives by a Palladium-Catalyzed Coupling Reaction of Aryl Halides with Isoquinoline-1,3(2 H,4 H)-diones.

The palladium-catalyzed cross-coupling reaction of aryl halides with isoquinoline-1,3(2 H,4 H)-diones for the synthesis of 4-aryl isoquinoline-1,3(2 H,4 H)-diones was developed. The reaction conditions exhibit remarkable compatibility with various aryl halides and isoquinoline-1,3(2 H,4 H)-diones, and the product could be conveniently transformed to 4-aryl tetrahydroisoquinolines. (±) Dichlorofensine was synthesized using this protocol in two steps with an overall yield of 71%.

Palladium-catalyzed direct C(sp3)-H arylation of indole-3-ones with aryl halides: a novel and efficient method for the synthesis of nucleophilic 2-monoarylated indole-3-ones.

A novel and efficient method for the synthesis of nucleophilic 2-monoarylated indole-3-ones via palladium-catalyzed direct C(sp3)-H arylation of indole-3-ones with aryl halides has been developed. Various 2-monoarylated indole-3-ones were readily obtained with yields up to 95%. As a class of important nucleophilic intermediates, 2-monoarylated indole-3-ones can be used for the construction of C2-quaternary indolin-3-one skeletons.

Disruption of biofilm formation by the human pathogen Acinetobacter baumannii using engineered quorum-quenching lactonases.

Acinetobacter baumannii is a major human pathogen associated with multidrug-resistant nosocomial infections; its virulence is attributed to quorum-sensing-mediated biofilm formation, and disruption of biofilm formation is an attractive antivirulence strategy. Here, we report the first successful demonstration of biofilm disruption in a clinical isolate of A. baumannii S1, using a quorum-quenching lactonase obtained by directed evolution; this engineered lactonase significantly reduced the biomass of A. baumannii-associated biofilms, demonstrating the utility of this antivirulence strategy.