Oxygen mediated oxidative couplings of flavones in alkaline water.

Catalyzed oxidative C-C bond coupling reactions play an important role in the chemical synthesis of complex natural products of medicinal importance. However, the poor functional group tolerance renders them unfit for the synthesis of naturally occurring polyphenolic flavones. We find that molecular oxygen in alkaline water acts as a hydrogen atom acceptor and oxidant in catalyst-free (without added catalyst) oxidative coupling of luteolin and other flavones. By this facile method, we achieve the synthesis of a small collection of flavone dimers and trimers including naturally occurring dicranolomin, philonotisflavone, dehydrohegoflavone, distichumtriluteolin, and cyclodistichumtriluteolin. Mechanistic studies using both experimental and computational chemistry uncover the underlying reasons for optimal pH, oxygen availability, and counter-cations that define the success of the reaction. We expect our reaction opens up a green and sustainable way to synthesize flavonoid dimers and oligomers using the readily available monomeric flavonoids isolated from biomass and exploiting their use for health care products and treatment of diseases.

Metabolic characterisation of eight Escherichia coli strains including "Big Six" and acidic responses of selected strains revealed by NMR spectroscopy.

The metabolic diversity of Escherichia coli strains (non-pathogenic E. coli ATCC 25922, and pathogenic E. coli O157:H7, O26:H11, O45:H2, O103:H11, O111, O121:H19, and O145) was tested using nuclear magnetic resonance. Based on two representative two-dimensional 1H-13C spectra, 38 metabolites were identified in E. coli intracellular samples. Principal component analysis indicated that metabolites including lysine, arginine, α-ketoglutaric acid, adenosine, and fumaric acid were responsible for the separation of E. coli ATCC 25922. Relatively large metabolic differences between ATCC 25922 and the pathogenic strains were recoded. The most varied pairwise group (ATCC 25922 vs. O26:H11) was further analysed. The screened metabolites and enrichment pathway tests revealed different amino acid metabolism and higher requirement for energy production in the pathogenic strains. The acidic responses of the selected strains were further tested. The in vitro and in vivo inactivation kinetics, morphological changes, and protein leakage showed higher acid tolerance of E. coli O26:H11. Metabolic analysis of the two strains under acidic stress revealed alternative metabolites and pathways in the two groups. Pathogenic O26:H11 was characterised by higher energy production and amino acid metabolism (lysine and glutamic acid). Real-time PCR tests confirmed that glutamic acid dependent decarboxylase/antiporter system was the major acid resistance mechanism.

Metabolic analysis of salicylic acid-induced chilling tolerance of banana using NMR.

Banana is highly susceptible to low temperature and salicylic acid (SA) can effectively improve the chilling tolerance. The metabolic changes of SA induced chilling responses of banana were studied. Bananas normally ripened under 15 °C and dramatic metabolic difference compared with other groups was recorded. Accumulation of glucose (>1.5 folds) and consumption of unsaturated fatty acids (11.0-16.5%) were observed. The glycolysis was induced to compensate the decreased energy charge. Low temperature (6 °C) caused chilling damage and metabolites including glutamine, serine, and glucose were related to chilled bananas. Various physiological changes such as sugar metabolism and consumption of reducing substances occurred to adapt the cold stress. SA released the cold injury and the disaccharides were increased by 18.1-21.4%. Further analysis revealed the synthesis of unsaturated fatty acids, amino acids such as proline, and enhanced energy charge. Thus, SA increased the chilling tolerance via a number of different metabolic mechanisms.

Elucidating antimicrobial mechanism of nisin and grape seed extract against Listeria monocytogenes in broth and on shrimp through NMR-based metabolomics approach.

Nisin and grape seed extract (GSE) have been widely used as food preservatives; however, the mechanism against pathogens at molecular level has not been well elucidated. This work aimed to investigate their antimicrobial effect against Listeria monocytogenes and to elucidate the mechanism by NMR-based metabolomics. Nisin exhibited enhanced in vitro antilisterial effect when combined with GSE (4.49 log CFU/mL reduction). Marked change in cell membrane permeability was observed in the combination group using confocal laser scanning microscopy; this was verified by increased leakage of protein and nucleic acid. The underlying antimicrobial mechanism was revealed by NMR coupled with multivariate analysis. Significant decreases in threonine, cysteine, ATP, NADP, adenine were observed, whereas a few of metabolites such as lactic acid and γ-aminobutyric acid (GABA) increased after nisin-GSE treatment (P < 0.05). Pathway analysis further manifested that the nisin-GSE inhibited the survival of L. monocytogenes by blocking the TCA cycle, amino acid biosynthesis and energy-producing pathway. Lastly, nisin and GSE were applied to shrimp and binary combination showed remarkably antilisterial activity (1.79 log CFU/g reduction). GABA shunt and protein degradation from shrimp compensated the unbalanced glycolysis and amino acid metabolism by providing energy and carbon source for L. monocytogenes inoculated on shrimp. Thus, they were more tolerant to nisin and GSE stresses as compared to the broth-grown culture.

Cyclohexyl-Fused, Spirobiindane-Derived, Phosphine-Catalyzed Synthesis of Tricyclic γ-Lactams and Kinetic Resolution of γ-Substituted Allenoates.

A C2-symmetric chiral phosphine catalyst, NUSIOC-Phos, which can be easily derived from cyclohexyl-fused spirobiindane, was introduced. A highly enantioselective domino process involving pyrrolidine-2,3-diones and γ-substituted allenoates catalyzed by NUSIOC-Phos has been disclosed. Diastereospecific tricyclic γ-lactams containing five contiguous stereogenic centers were obtained in high yields and with nearly perfect enantioselectivities. A kinetic resolution process of racemic γ-substituted allenoates was developed for the generation of optically enriched chiral allenoates.

Comparison of metabolic response between the planktonic and air-dried Escherichia coli to electrolysed water combined with ultrasound by 1H NMR spectroscopy.

The antimicrobial effects of electrolysed water and ultrasound have been well reported; however, little attention was paid to their effects on the metabolite changes of bacteria in different states. In this study, the metabolomic variations of Escherichia coli ATCC 25922 in planktonic and adherent state (air-dried on stainless steel coupons) after the combination treatment of low-concentration acidic electrolysed water (AEW, free available chlorine (FAC): 4 mg/L) and ultrasound were characterised, by conducting multivariate data analysis based on nuclear magnetic resonance (NMR) spectroscopy. Overall, 43 metabolites were identified in two states of E. coli, including a wide range of amino acids, organic acids, nucleotides and their derivatives. The quantification of whole-cell metabolism in planktonic and air-dried cultures was quite different: air-dried E. coli exhibited more resistance to ultrasound and AEW treatments due to initiating a protective response against oxidative and acid stresses, which was not observed in planktonic E. coli, whose levels of all identified metabolites were decreased significantly after the combined treatment. Further pathway analysis revealed that alanine, aspartate and glutamate metabolism, glycolysis, pyruvate metabolism and tricarboxylic acid (TCA) cycle were changed significantly in planktonic culture, but to a less extent in air-dried culture, in which some shifts in glutamate decarboxylase (GAD) system and some shunts like mixed acid fermentation and pentose phosphate pathway were observed for maintaining metabolic balance. These findings suggest that NMR-based metabolomics strategy is promising in identifying different metabolic shifts in different states of bacteria. They also provide some guidance for food equipment sanitisation, especially for organic food processing.

Effect of vacuum impregnated fish gelatin and grape seed extract on metabolite profiles of tilapia (Oreochromis niloticus) fillets during storage.

Traditional methods evaluating fish quality do not involve comprehensive qualification and quantification of quality-related components. The objective of this study was to investigate the effect of vacuum impregnated fish gelatin (FG) and grape seed extract (GSE) on metabolites of tilapia fillets during storage using nuclear magnetic resonance (NMR). Totally 42 metabolites were identified, 36 of which were quantified. The multivariate analysis results demonstrated distinct separations between fresh and stored fillets, indicating significant metabolite changes during storage. Some metabolites like choline and trimethylamine oxide were closely related to freshness while organic acids were associated with spoilage. Combined FG and GSE reduced the formation of undesirable metabolites like trimethylamine and histidine significantly (P < 0.05). Traditional freshness indexes indicated preserved quality after combined coating and further verified NMR results. This study reveals the potential of NMR to analyse metabolites that determine fish quality and to monitor their changes during storage.

Metabolomic analysis of energy regulated germination and sprouting of organic mung bean (Vigna radiata) using NMR spectroscopy.

Germination and sprouting are regulated by the energy status. In the present study, mung bean seeds were treated with adenosine triphosphate and 2,4-dinitrophenol (DNP). The metabolomic changes during development of mung beans under different energy statuses were investigated. In total, 42 metabolites were identified. Principal component analysis revealed that the featured compounds produced in seeds were oleic, linoleic, and succinic acids. Sugars, including maltose, sucrose, and glucose were related to sprouting. Mung bean seeds utilised diverse energy resources and produced higher succinic acid content. Sugars and secondary metabolites accumulated in sprouts. Nitrogen, sugar, and amino acid metabolism pathways contributed to this physiological process. DNP caused an energy deficit, which resulted in the consumption and translation of glucose. Higher contents of other saccharides and amino acids were observed. The transcriptional results further confirmed our metabolic hypothesis. In conclusion, sufficient energy supply is crucial for sprout development and nutritive metabolite synthesis.

Graphene-Oxide-Catalyzed Direct CH-CH-Type Cross-Coupling: The Intrinsic Catalytic Activities of Zigzag Edges.

The development of graphene oxide (GO)-based materials for C-C cross-coupling represents a significant advance in carbocatalysis. Although GO has been used widely in various catalytic reactions, the scope of reactions reported is quite narrow, and the relationships between the type of functional groups present and the specific activity of the GO are not well understood. Herein, we explore CH-CH-type cross-coupling of xanthenes with arenes using GO as real carbocatalysts, and not as stoichiometric reactants. Mechanistic studies involving molecular analogues, as well as trapped intermediates, were carried out to probe the active sites, which were traced to quinone-type functionalities as well as the zigzag edges in GO materials. GO-catalyzed cross-dehydrogenative coupling is operationally simple, shows reusability over multiple cycles, can be conducted in air, and exhibits good functional group tolerance.

Metabolite profiling of Listeria innocua for unravelling the inactivation mechanism of electrolysed water by nuclear magnetic resonance spectroscopy.

Bactericidal effects of low concentration electrolysed water (LcEW) on microorganisms are previously well reported; however, the inactivation mechanism of EW is not understood. The lethal and sublethal injuries of L. monocytogenes and L. innocua by EW treatments were determined and the metabolic profile changes for L. innocua were characterised using nuclear magnetic resonance (NMR). Microbial metabolomics approach combined with multivariate data analyses was used to interpret the cellular chemical fingerprints of L. innocua. The relative amount of intracellular reactive oxygen species (ROS) was assayed using 2',7-dichlorodihydrofluorescein diacetate (H2DCFDA). The results showed that the proportion of the sublethally injured microbial cells L. monocytogenes and L. innocua increased from 40% to 70% and from 35% to 65%, respectively, when the free available chlorine (FAC) of LcEW increased from 2 to 8 mg/L. Overall, 36 low-molecular-weight metabolic compounds in L. innocua extracts were characterised by NMR spectroscopy. EW perturbation resulted in a drastic and multitude disruption across a wide range of biochemical process including peptidoglycan synthesis, nucleotides biosynthesis and amino acid metabolism. Elevated levels of α-ketoglutarate and succinate implicated the enhanced glutamate decarboxylase (GAD) system and γ-aminobutyric acid (GABA) shunt for the protection against oxidative stress. These findings provided the comprehensive insights into the metabolic response of Listeria to EW oxidative stress and can serve as a basis for better utilisation for sanitisation.

Identification of Cyclic Dipeptides from Escherichia coli as New Antimicrobial Agents against Ralstonia Solanacearum.

Ralstonia solanacearum is a causative agent of bacterial wilt in many important crops throughout the world. How to control bacterial wilt caused by R. solanacearum is a major problem in agriculture. In this study, we aim to isolate the biocontrol agents that have high efficacy in the control of bacterial wilt. Three new bacterial strains with high antimicrobial activity against R. solanacearum GMI1000 were isolated and identified. Our results demonstrated that these bacteria could remarkably inhibit the disease index of host plant infected by R. solanacearum. It was indicated that strain GZ-34 (CCTCC No. M 2016353) showed an excellent protective effect to tomato under greenhouse conditions. Strain GZ-34 was characterized as Escherichia coli based on morphology, biochemistry, and 16S rRNA analysis. We identified that the main antimicrobial compounds produced by E. coli GZ-34 were cyclo(l-Pro-d-Ile) and cyclo(l-Pro-l-Phe) using electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) analysis. The two active compounds also interfered with the expression levels of some pathogenicity-contributors of R. solanacearum. Furthermore, cyclo(l-Pro-l-Phe) effectively inhibited spore formation of Magnaporthe grisea, which is a vital pathogenesis process of the fungal pathogen, suggesting cyclic dipeptides from E. coli are promising potential antimicrobial agents with broad-spectrum activity to kill pathogens or interfere with their pathogenesis.

Divergent reactivities in fluoronation of allylic alcohols: synthesis of Z-fluoroalkenes via carbon-carbon bond cleavage.

An unconventional cleavage of an unstrained carbon-carbon bond in allylic alcohols can be induced by the use of N-fluorobenzenesulfonimide (NFSI) under catalyst-free conditions. By using this simple procedure, a wide range of functionalized Z-fluoroalkenes can be accessed in high yield and selectivity from cyclic and acyclic allylic alcohols.

Three-component reactions of isocyanoacetates, amines and 3-formylchromones initiated by an unexpected aza-Michael addition.

We present herein a new mode of three-component reactions between isocyanoacetates, amines and 3-formylchromones. Both experimental and DFT studies revealed that this Ag-catalyzed unusual transformation is initiated by a facile aza-Michael addition instead of the conventional imine condensation. This catalytic method enables an efficient synthesis of polysubstituted pyrroles.

Fused Bicyclic Caspase-1 Inhibitors Assembled by Copper-Free Strain-Promoted Alkyne-Azide Cycloaddition (SPAAC).

Challenges exist in the development of potent and selective small-molecule inhibitors against caspase-1. Herein, by making use of the copper-free strain-promoted alkyne-azide cycloaddition (SPAAC) reaction between difluorinated cyclooctynes (DIFOs) and various azide-containing compounds, we showed for the first time that potential caspase-1 inhibitors could be rapidly synthesized. The resulting fused bicyclic compounds structurally resembled the central portion (P2 -P3 ) of Pralnacasan (a well-known small molecule caspase-1 inhibitor), with diversity at the P4 -position of the parental inhibitor conveniently installed from the azide component. Since our SPAAC-assembled inhibitor library was synthesized by using a copper-free bioorthogonal chemistry, the resulting 52-membered library (2 DIFOs×26 azides) was immediately ready for subsequent cell-based screening for rapid identification of potential cell-permeable hits capable of effectively inhibiting endogenous caspase-1 activities. C1FS, a recently reported fluorogenic two-photon probe, which possesses improved live-cell imaging sensitivity against endogenous caspase-1, was used both in vitro and in LPS/ATP-induced macrophages (a well-established caspase-1-activated cell model) to screen against selected compounds from the above-mentioned library, leading to subsequent discovery of a novel caspase-1 inhibitor named b7-b.

Enantioselective desymmetrization of cyclohexadienones via an intramolecular Rauhut-Currier reaction of allenoates.

The Rauhut-Currier (RC) reaction represents an efficient method for the construction of carbon-carbon bond in organic synthesis. However, the RC reactions involving allenoate substrates are very rare, and in particular, asymmetric intramolecular RC reaction of allenoates is yet to be discovered. Here, we show that the intramolecular RC reaction proceeds smoothly in the presence of 1 mol% ß-ICD, and bicyclic lactones are obtained in high yields and with excellent enantiomeric excesses. With the employment of γ-substituted allenoates as racemic precursors, a novel dynamic kinetic resolution of allenes via RC reaction is observed, which allows for facile synthesis of highly enantiomerically enriched allenes.

Synthesis of Disubstituted 3-Phenylimidazo[1,2-a]pyridines via a 2-Aminopyridine/CBrCl3 α-Bromination Shuttle.

A versatile protocol for the synthesis of disubstituted 3-phenylimidazo[1,2-a]pyridines by coupling 2-aminopyridine with phenylacetophenones, phenylacetones, or ß-tetralone has been developed. Isolated yields of up to 97% were obtained at 80 °C within 5 h. The 2-aminopyridine/CBrCl3 system acts as an α-bromination shuttle by transferring Br from CBrCl3 to the α-carbon of the carbonyl moiety. This triggers a series of steps with double C-N/C-N bond formation to the final product. The distinct advantages of this protocol include the use of commercially available inexpensive substrates, simplicity of a metal-free one-pot synthesis, and ease of scale-up to multigram quantities.

Highly emissive, solution-processable and dynamic Eu(III)-containing coordination polymers.

A new class of soluble Eu(III) coordination polymers based on a tridentate ditopic pybox ligand has been developed displaying high metal emission quantum yields of up to 73% as well as a unique dynamic behaviour in solution.

The host plant metabolite glucose is the precursor of diffusible signal factor (DSF) family signals in Xanthomonas campestris.

Plant pathogen Xanthomonas campestris pv. campestris produces cis-11-methyl-2-dodecenoic acid (diffusible signal factor [DSF]) as a cell-cell communication signal to regulate biofilm dispersal and virulence factor production. Previous studies have demonstrated that DSF biosynthesis is dependent on the presence of RpfF, an enoyl-coenzyme A (CoA) hydratase, but the DSF synthetic mechanism and the influence of the host plant on DSF biosynthesis are still not clear. We show here that exogenous addition of host plant juice or ethanol extract to the growth medium of X. campestris pv. campestris could significantly boost DSF family signal production. It was subsequently revealed that X. campestris pv. campestris produces not only DSF but also BDSF (cis-2-dodecenoic acid) and another novel DSF family signal, which was designated DSF-II. BDSF was originally identified in Burkholderia cenocepacia to be involved in regulation of motility, biofilm formation, and virulence in B. cenocepacia. Functional analysis suggested that DSF-II plays a role equal to that of DSF in regulation of biofilm dispersion and virulence factor production in X. campestris pv. campestris. Furthermore, chromatographic separation led to identification of glucose as a specific molecule stimulating DSF family signal biosynthesis in X. campestris pv. campestris. (13)C-labeling experiments demonstrated that glucose acts as a substrate to provide a carbon element for DSF biosynthesis. The results of this study indicate that X. campestris pv. campestris could utilize a common metabolite of the host plant to enhance DSF family signal synthesis and therefore promote virulence.

Biosynthesis of mupirocin by Pseudomonas fluorescens NCIMB 10586 involves parallel pathways.

Mupirocin, a clinically important antibiotic produced via a trans-AT Type I polyketide synthase (PKS) in Pseudomonas fluorescens, consists of a mixture of mainly pseudomonic acids A, B, and C. Detailed metabolic profiling of mutant strains produced by systematic inactivation of PKS and tailoring genes, along with re-feeding of isolated metabolites to mutant stains, has allowed the isolation of a large number of novel metabolites, identification of the 10,11-epoxidase, and full characterization of the mupirocin biosynthetic pathway, which proceeds via major (10,11-epoxide) and minor (10,11-alkene) parallel pathways.

New stilbenoids isolated from fungus-challenged black skin peanut seeds and their adipogenesis inhibitory activity in 3T3-L1 cells.

One new stilbene derivative (3,5,3'-trihydroxy-4'-methoxy-5'-isopentenylstilbene, MIP) and two new stilbene dimers (arahypin-11 and arahypin-12) together with three known stilbenoids (arachidin-1, arachidin-3, and SB-1) were isolated from black skin peanut seeds challenged by the fungal strain Rhizopus oligoporus . The structures of the three new compounds were elucidated by analysis of HRESIMS, UV, 1D and 2D NMR spectra. The antiadipogenic and cytotoxic effects of the isolated compounds were investigated using 3T3-L1 cells at a concentration range of 1-10 µM. Among the compounds tested, arachidin-1 inhibited the 3T3-L1 adipocyte differentiation dose-dependently, whereas arahypin-11 and arahypin-12 exhibited significant cytotoxicity in 3T3-L1 preadipocytes.