Potent synergy and sustained bactericidal activity of polymyxins combined with Gram-positive only class of antibiotics versus four Gram-negative bacteria.

BACKGROUND: Gram-negative bacteria (GNB) are becoming increasingly resistant to a wide variety of antibiotics. There are currently limited treatments for GNB, and the combination of antibiotics with complementary mechanisms has been reported to be a feasible strategy for treating GNB infection. The inability to cross the GNB outer membrane (OM) is an important reason that a broad spectrum of Gram-positive only class of antibiotics (GPOAs) is lacking. Polymyxins may help GPOAs to permeate by disrupting OM of GNB. OBJECTIVE: To identify what kind of GPOAs can be aided to broaden their anti-GNB spectrum by polymyxins, we systematically investigated the synergy of eight GPOAs in combination with colistin (COL) and polymyxin B (PMB) against GNB in vitro. METHODS: The synergistic effect of COL or PMB and GPOAs combinations against GNB reference strains and clinical isolates were determined by checkerboard tests. The killing kinetics of the combinations were assessed using time-kill assays. RESULTS: In the checkerboard tests, polymyxins-GPOAs combinations exert synergistic effects characterized by species and strain specificity. The synergistic interactions on P. aeruginosa strains are significantly lower than those on strains of A. baumannii, K. pneumoniae and E. coli. Among all the combinations, COL has shown the best synergistic effect in combination with dalbavancin (DAL) or oritavancin (ORI) versus almost all of the strains tested, with FICIs from 0.16 to 0.50 and 0.13 to < 0.28, respectively. In addition, the time-kill assays demonstrated that COL/DAL and COL/ORI had sustained bactericidal activity. CONCLUSIONS: Our results indicated that polymyxins could help GPOAs to permeate the OM of specific GNB, thus showed synergistic effects and bactericidal effects in the in vitro assays. In vivo combination studies should be further conducted to validate the results of this study.

Electrochemical stereoselective synthesis of polysubstituted 1,4-dicarbonyl Z-alkenes via three-component coupling of sulfoxonium ylides and alkynes with water.

The first straightforward strategy for the synthesis of 1,4-dicarbonyl Z-alkenes has been developed via an electrochemical cross-coupling reaction of sulfoxonium ylides and alkynes with water. The metal-free protocol showed an easy-to-handle nature, good functional group tolerance, and high Z-stereoselectivity, which is rare in previous cases. The proposed reaction mechanism was convincingly established by carrying out a series of control experiments, cyclic voltammetry experiments, and density functional theory (DFT) studies.

Electrochemical chemoselective hydrogenation of 1,4-enediones with HFIP as the hydrogen donor: scalable access to 1,4-diketones.

A straightforward electrochemical protocol for efficient hydrogenation of unsaturated CC bonds has been reported in an undivided cell. A series of versatile 1,4-diketones are smoothly generated under metal-free and external-reductant-free electrolytic conditions. Moreover, the tolerance of various functional groups and decagram-scale experiments have shown the practicability and potential applications of this methodology. Moreover, a range of heterocyclic compounds were easily prepared through follow-up procedures of 1,4-diketones.

SO42- ions as a nucleophilic reagent: straightforward electrochemical access to organosulfates.

An electrooxidation direct difunctionalization of alkynes with sulfonyl hydrazides has been developed for the construction of sulfonyl alkenyl sulfates in the absence of metal catalysts and a stoichiometric amount of oxidants. Notably, it is the first example to verify that SO42- ions can act as a nucleophilic reagent for the preparation of organosulfates.

A guide to organic electroreduction using sacrificial anodes.

Organic electrosynthesis is a green strategy for the synthesis of valuable molecules. Electrochemical reactions using sacrificial metal anodes enable new reactivity to be uncovered that could not be achieved with traditional non-electrochemical methods. Compared with reactions using metal powder as the reducing reagent, the mild electroreduction protocols usually exhibit diverse reactivity and excellent selectivity. The inexpensive metal anodes possess low oxidation potential, which could prevent undesired overoxidation of substrates, active intermediates and products. The in situ generated metal ions from sacrificial anodes could not only serve as Lewis acids to activate the reactants but also as a promoter or mediator. This tutorial review highlights the recent achievements in this rapidly growing area within the past five years. The sacrificial anode-enabled electroreductions are discussed according to the reaction type.

Selective Electrochemical Synthesis of 9-Aryl-10-sulfonyl Substituted Phenanthrene from Alkynes and Sulfonyl Hydrazides.

An efficient electrochemical synthesis of sulfonated phenanthrenes via the reaction of internal alkynes with sulfonyl hydrazides has been established. The protocol does not require a metal catalyst or external oxidants, providing a green and mild route to functionalized phenanthrenes. Moreover, the compatibility of various functional groups and decagram-scale experimental conditions demonstrate the practicality of the electrochemical strategy.

Electrochemically-promoted synthesis of benzo[b]thiophene-1,1-dioxides via strained quaternary spirocyclization.

We report an approach for the synthesis of benzothiophene motifs under electrochemical conditions by the reaction of sulfonhydrazides with internal alkynes. Upon the formation of a quaternary spirocyclization intermediate by the selective ipso-addition instead of an ortho-attack, the S-migration process was rationalized to lead to the products. Computational studies revealed the selectivity and the compatibility of drug molecules showcased the potential application of the protocols.

Electrochemically Promoted [3 + 2] Annulation of Imidazo[1,2-a]pyridine with Alkynes.

The efficient electrochemically promoted [3 + 2] annulation of imidazo[1,2-a]pyridines with alkynes using traceless electrons as green reagents has been developed, leading to the synthesis of a large class of polycyclic heteroaromatics in good yields with a broad substrate scope under mild and green conditions. The scaled-up experiment, follow-up procedures, and potential biological applications show the practicability and feasibility of the electrochemical method.

[Variety of the Composition and Sources of VOCs During the Spring Festival and Epidemic Prevention in the Pearl River Delta].

Volatile organic compounds (VOCs) are the key precursors of the ozone (O3) formation processes in the troposphere and are important control objects for the coordinated governance of O3 and PM2.5. The Spring Festival of 2020 was affected by the novel coronavirus (COVID-19) pneumonia epidemic:companies stopped work and production, and traffic was restricted, providing scientific experimentation opportunities for pollutant emission reduction research. This study analyzed the variety of the composition, chemical reaction activity, and sources of VOCs in the Pearl River Delta during the Spring Festival and the epidemic control period, using real-time online monitoring data of VOCs obtained at four sites(Guangzhou, Dongguan, Zhongshan, and Duanfen)in the Pearl River Delta from January 1, 2020 to February 29, 2020. The results showed that during the Spring Festival and the epidemic control period, the average of φ (VOCs) in the Pearl River Delta was 15.89×10-9, and the maximum hourly average concentration was 45.43×10-9, values that were 44% and 60% lower, respectively, than those before the Spring Festival holiday. Among the VOCs component concentration decreases, the aromatic hydrocarbon component decreased the most, and the decrease in the urban area of the Pearl River Delta (74%) was significantly greater than that in the suburban area (56%). As a result, the contribution rate of aromatic hydrocarbons to the total VOCs was reduced to less than 10%. The analysis of the·OH reaction activity of VOCs(L·OH)and ozone formation potential(OFP)showed that the L·OH and OFP of VOCs decreased significantly in the Pearl River Delta during the Spring Festival and the epidemic control period. Compared with those before the Spring Festival holiday, the total L·OH and total OFP decreased by an average of 60% and 63% in the urban area of the Pearl River Delta, respectively. Additionally, the atmospheric oxidation had also been significantly reduced, which showed a 28% decrease in ρ(Ox). The ratio of toluene/benzene showed that the influence of industrial sources had almost disappeared during the Spring Festival and the epidemic control period, and the total points of the representative components of industrial-related solvent-use sources such as toluene, ethylbenzene, and m/p-xylene dropped by 72% to 91%. The results of this study suggest that solvent-use sources and vehicle exhaust emission sources are the current sources of VOCs that need to be paid attention to in the prevention and control of O3 pollution in the Pearl River Delta region, and the impact of petrochemical sources cannot be ignored in the work of further reducing the background concentration of O3.

Electrochemical Benzylic C(sp3)-H Isothiocyanation.

Selective C(sp3)-H isothiocyanation represents a significant strategy for the synthesis of isothiocyanate derivatives. We report herein an electrochemical benzylic isothiocyanation in a highly chemo- and site-selective manner under external oxidant-free conditions. The high chemoselectivity is attributed to the facile in situ isomerization of benzylic thiocyanates to isothiocyanates. Notably, the method exhibits high functional group compatibility and is suitable for late-stage functionalization of bioactive molecules.

Hypervalent iodine promoted the synthesis of cycloheptatrienes and cyclopropanes.

A new strategy is reported for intramolecular Buchner-type reactions using PIDA as a promotor. Traditionally, the Buchner reaction is achieved via Rh-carbenoids derived from RhII catalysts with diazo compounds. Herein, the first metal-free Buchner-type reaction to construct highly strained cycloheptatriene- and cyclopropane-fused lactams is presented. The advantage of these transformations is in their mild reaction conditions, simple operation, broad functional group compatibility and rapid synthetic protocol. In addition, scaled-up experiments and a series of follow-up synthetic procedures were performed to clarify the flexibility and practicability of this method. DFT calculations were carried out to clarify the mechanism.

Combined effect of Polymyxin B and Tigecycline to overcome Heteroresistance in Carbapenem-Resistant Klebsiella pneumoniae.

We assessed the prevalence of polymyxin B (PMB)- and tigecycline (TGC)-heteroresistant Klebsiella pneumoniae isolates and investigated the combined effect of PMB and TGC against dual-heteroresistant K. pneumoniae. Ninety-five nonduplicated carbapenem-resistant K. pneumoniae (CRKP) clinical isolates were collected from a tertiary-care teaching hospital in China. PCR was used to detect the resistant genes among the CRKP isolates. Population analysis profiling (PAP) was carried out to evaluate the existence of heteroresistance. A time-kill assay of PMB combined with TGC was conducted against heteroresistant K. pneumoniae strains. Real-time PCR was performed to determine the pmrA, phoP, and acrB expression levels. Among them, 74 isolates (77.9%) were susceptible to TGC, and 90 isolates (94.7%) were susceptible to PMB. In addition, of the TGC-susceptible isolates, 49 strains (66.2%) exhibited heteroresistant phenotypes. All of the PMB-susceptible isolates showed heteroresistant phenotypes. Forty-six isolates (48.4%) were heteroresistant to both TGC and PMB. All of the isolates carried the blaKPC gene, and one strain carried both blaKPC and blaNDM genes. The time-kill assay revealed in four isolates that early bactericidal activity could be triggered by the combination of PMB and TGC, and there was no regrowth, even at a relatively lower concentration (0.125 mg/liter PMB with 1 mg/liter TGC). Upregulated expression of pmrA, phoP, and acrB indicated that heteroresistance could be related to two-component systems and the AcrAB-TolC efflux pump. The combination of PMB and TGC may be a treatment strategy for those infected with CRKP heteroresistant to PMB and/or TGC. IMPORTANCE Tigecycline and colistin are two of the last treatment options remaining for carbapenem-resistant Enterobacteriaceae. Unfortunately, tigecycline resistance and colistin heteroresistance are also increasing rapidly. In the current study, we identified a high prevalence of heteroresistance to both PMB and TGC among clinical isolates of carbapenem-resistant K. pneumoniae (CRKP). The resistant subpopulations could survive pressure from TGC or PMB but were killed by the combination at a relatively low dose. It is proposed that the combination of PMB and TGC may be a treatment strategy for patients who are infected with CRKP heteroresistant to PMB or TGC.

Reducing Defects Density and Enhancing Hole Extraction for Efficient Perovskite Solar Cells Enabled by π-Pb2+ Interactions.

Molecular doping is an of significance approach to reduce defects density of perovskite and to improve interfacial charge extraction in perovskite solar cells. Here, we show a new strategy for chemical doping of perovskite via an organic small molecule, which features a fused tricyclic core, showing strong intermolecular π-Pb2+ interactions with under-coordinated Pb2+ in perovskite. This π-Pb2+ interactions could reduce defects density of the perovskite and suppress the nonradiative recombination, which was also confirmed by the density functional theory calculations. In addition, this doping via π-Pb2+ interactions could deepen the surface potential and downshift the work function of the doped perovskite film, facilitating the hole extraction to hole transport layer. As a result, the doped device showed high efficiency of 21.41 % with ignorable hysteresis. This strategy of fused tricyclic core-based doping provides a new perspective for the design of new organic materials to improve the device performance.

Nickel-promoted oxidative domino Csp3-H/N-H bond double-isocyanide insertion reaction to construct pyrrolin-2-ones.

The first nickel-catalyzed oxidative domino Csp3-H/N-H double isocyanide insertion reaction of acetamides with isocyanides has been developed for the synthesis of pyrrolin-2-one derivatives. A wide range of acetamides bearing various functional groups are compatible with this reaction system by utilizing Ni(acac)2 as a catalyst. In this transformation, isocyanide could serve as a C1 connector and insert into the inactive Csp3-H bond, representing an effective way to construct heterocycles.

The ruthenium(ii)-catalyzed C-H olefination of indoles with alkynes: the facile construction of tetrasubstituted alkenes under aqueous conditions.

An environmentally-friendly and facile protocol for the construction of tetrasubstituted alkenes has been established with Ru(ii)-catalyzed C-H bond functionalizations under mild conditions. The method features the usage of readily available substrates, without external oxidants and additives, 100% atom economy, and excellent regioselectivity, thus enhancing the practicability of this protocol. Moreover, this transformation proceeded smoothly under aqueous conditions and could be extended to the gram scale. N-Methoxyamide, as a directing group (DG), played a vital role in the transformation.

InCl3-catalyzed 5-exo-dig cyclization/1,6-conjugate addition of N-propargylamides with p-QMs to construct oxazole derivatives.

An InCl3-catalyzed atom-economic intramolecular 5-exo-dig cyclization/1,6-conjugate addition/aromatization of N-propargylamides with p-QMs to produce oxazoles tethering diarylmethane has been successfully developed. InCl3 not only served as Lewis acid to catalyze the cyclization of propargylic amides but also activated the carbonyl of p-QMs to achieve the 1,6-addition process in a one-pot manner. The reaction has attractive features, including mild reaction conditions, broad scope of substrates, good yields, and scalability.

Fast construction of isoquinolin-1(2H)-ones by direct intramolecular C-H/N-H functionalization under metal-free conditions.

The general protocol for the synthesis of isoxazolidine-fused isoquinolin-1(2H)-ones was established with the help of bench stable hypervalent iodine reagent PIDA. Polycyclic six-, seven- and eight-membered N-heterocycles can be rapidly synthesized from available amides under metal-free conditions within 1 min at room temperature through C-H/N-H functionalization. Moreover, the protocol has the merits of broad substrate scope, atom economy and operational simplicity.

Silver-promoted regioselective [4+2] annulation reaction of indoles with alkenes to construct dihydropyrimidoindolone scaffolds.

An AgI-promoted regioselective [4+2] annulation reaction of indoles with alkenes has been established. During the transformation, N-centered radicals are generated by the oxidation of the N-H bond of N-alkoxyamides. Control experiments and DFT calculations reveal a plausible mechanism. This synergistic process achieves the direct construction of new C-C and C-N bonds under relatively mild conditions with broad substrate scope, high atom economy, and easy-to-handle nature.

N-Phenoxyamides as Multitasking Reagents: Base-Controlled Selective Construction of Benzofurans or Dihydrobenzofuro[2,3- d]oxazoles.

An efficient method to selectively construct benzofuran and dihydrobenzofuro[2,3- d]oxazole derivatives has been successfully established by means of base-controlled cyclization of N-phenoxyamides with 1-[(triisopropylsilyl)ethynyl]-1,2-benziodoxol-3(1 H)-one (TIPS-EBX). N-phenoxyamides as multitasking reagents have triggered two different cascade reaction sequences. This is the first example of using TIPS-EBX for the transformation of C(sp) to either C(sp2) or C(sp3) under metal-free conditions.

One Base for Two Shots: Metal-Free Substituent-Controlled Synthesis of Two Kinds of Oxadiazine Derivatives from Alkynylbenziodoxolones and Amidoximes.

Different 1,2-migrations and cyclizations of a variety of alkynylbenziodoxolones (EBXs) and amidoximes under one-base conditions are described. This process provides an efficient protocol for the divergent synthesis of two oxadiazine derivatives via switchable selectivity of EBXs controlled by simply varying the substituents of the amidoximes, which feature transition metal-free conditions, simple execution, and high chemoselectivity.