Showing papers in "Organic and Biomolecular Chemistry in 2010"
TL;DR: This gel-state NMR fingerprinting of the components of finely divided plant cell walls swelled in DMSO may provide the basis for an attractive approach to providing a secondary screen for selecting biomass lines and for optimizing biomass processing and conversion efficiencies.
Abstract: NMR fingerprinting of the components of finely divided plant cell walls swelled in DMSO has been recently described. Cell wall gels, produced directly in the NMR tube with perdeutero-dimethylsulfoxide, allowed the acquisition of well resolved/dispersed 2D 13C–1H correlated solution-state NMR spectra of the entire array of wall polymers, without the need for component fractionation. That is, without actual solubilization, and without apparent structural modification beyond that inflicted by the ball milling and ultrasonication steps, satisfactorily interpretable spectra can be acquired that reveal compositional and structural details regarding the polysaccharide and lignin components in the wall. Here, the profiling method has been improved by using a mixture of perdeuterated DMSO and pyridine (4 : 1, v/v). Adding pyridine provided not only easier sample handling because of the better mobility compared to the DMSO-d6-only system but also considerably elevated intensities and improved resolution of the NMR spectra due to the enhanced swelling of the cell walls. This modification therefore provides a more rapid method for comparative structural evaluation of plant cell walls than is currently available. We examined loblolly pine (Pinus taeda, a gymnosperm), aspen (Populus tremuloides, an angiosperm), kenaf (Hibiscus cannabinus, an herbaceous plant), and corn (Zea mays L., a grass, i.e., from the Poaceae family). In principle, lignin composition (notably, the syringyl : guaiacyl : p-hydroxyphenyl ratio) can be quantified without the need for lignin isolation. Correlations for p-coumarate units in the corn sample are readily seen, and a variety of the ferulate correlations are also well resolved; ferulates are important components responsible for cell wall cross-linking in grasses. Polysaccharide anomeric correlations were tentatively assigned for each plant sample based on standard samples and various literature data. With the new potential for chemometric analysis using the 2D NMR fingerprint, this gel-state method may provide the basis for an attractive approach to providing a secondary screen for selecting biomass lines and for optimizing biomass processing and conversion efficiencies.
566 citations
TL;DR: An account of the activation strain model of chemical reactivity and its recent applications is provided to arrive at a qualitative understanding of the trends in activation barriers and transition-state geometries in terms of the reactants' properties.
Abstract: Herein, we provide an account of the activation strain model of chemical reactivity and its recent applications. In this model, the potential energy surface ΔE(ζ) along the reaction coordinate ζ is decomposed into the strain ΔEstrain(ζ) of the increasingly deformed reactants plus the interaction ΔEint(ζ) between these deformed reactants, i.e., ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). The purpose of this fragment-based approach is to arrive at a qualitative understanding, based on accurate calculations, of the trends in activation barriers and transition-state geometries (e.g., early or late along the reaction coordinate) in terms of the reactants’ properties. The usage of the activation strain model is illustrated by a number of concrete applications, by us and others, in the fields of catalysis and organic chemistry.
551 citations
TL;DR: In this article, transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon−nitrogen and sulfur-nitrogen bonds, which are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the byproduct of the reaction is environmentally benign N2 gas.
Abstract: Transition metal-catalyzed N-atom transfer reactions of azides provide efficient ways to construct new carbon–nitrogen and sulfur–nitrogen bonds. These reactions are inherently green: no additive besides catalyst is needed to form the nitrenoid reactive intermediate, and the by-product of the reaction is environmentally benign N2 gas. As such, azides can be useful precursors for transition metal-catalyzed N-atom transfer to sulfides, olefins and C–H bonds. These methods offer competitive selectivities and comparable substrate scope as alternative processes to generate metal nitrenoids.
355 citations
TL;DR: The combined results indicate a sufficiently low toxicity of cucurbit[n] as additives for medicinal and pharmaceutical use, and the bioadaptability of the compounds was further examined through in vivo studies on mice.
Abstract: Cucurbit[n]urils (CB[n]) are potential stabilizing, solubilizing, activating, and delivering agents for drugs. The toxicity of the macrocyclic host molecules cucurbit[7]uril (CB[7]), the most water-soluble homologue, as well as cucurbit[8]uril (CB[8]) has been evaluated. In vitro studies on cell cultures revealed an IC50 value of 0.53 ± 0.02 mM for CB[7], corresponding to around 620 mg of CB[7] per kg of cell material. Live-cell imaging studies performed on cells treated with subtoxic amounts of CB[7] showed no detrimental effects on the cellular integrity as assessed by mitochondrial activity. For CB[8], no significant cytotoxicity was observed within its solubility range. The bioadaptability of the compounds was further examined through in vivo studies on mice, where intravenous administration of CB[7] showed a maximum tolerated dosage of 250 mg kg−1, while oral administration of a CB[7]/CB[8] mixture showed a tolerance of up to 600 mg kg−1. The combined results indicate a sufficiently low toxicity to encourage further exploration of CB[n] as additives for medicinal and pharmaceutical use.
329 citations
TL;DR: The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel-Crafts, aza-ene- type, Diels-Alder, as well as cascade and multi-component reactions.
Abstract: BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Bronsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C–C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on hydrocyanations, aldol-type, Mannich, Friedel–Crafts, aza-ene-type, Diels–Alder, as well as cascade and multi-component reactions.
305 citations
TL;DR: The close chemical relationship between tellurium and sulfur also transcends into in vitro and in vivo situations and provides new impetus for the development of enzyme inhibitors and redox modulators, some of which may be of interest in the field of antibiotics and anticancer drug design.
Abstract: Tellurium has long appeared as a nearly 'forgotten' element in Biology, with most studies focusing on tellurite, tellurate and a handful of organic tellurides. During the last decade, several discoveries have fuelled a renewed interest in this element. Bioincorporation of telluromethionine provides a new approach to add heavy atoms to selected sites in proteins. Cadmium telluride (CdTe) nanoparticles are fluorescent and may be used as quantum dots in imaging and diagnosis. The antibiotic properties of tellurite, long known yet almost forgotten, have attracted renewed interest, especially since the biochemical mechanisms of tellurium cytotoxicity are beginning to emerge. The close chemical relationship between tellurium and sulfur also transcends into in vitro and in vivo situations and provides new impetus for the development of enzyme inhibitors and redox modulators, some of which may be of interest in the field of antibiotics and anticancer drug design.
277 citations
TL;DR: The case of quadruplexes formed by monomeric guanosine derivatives, where there is no strand connecting the adjacent quartets and the definition parallel/antiparallel strands cannot apply, will be discussed.
Abstract: G-quadruplex DNA (G4-DNA) structures are four-stranded helical DNA (or RNA) structures, comprising stacks of G-tetrads, which are the outcome of planar association of four guanines in a cyclic Hoogsteen hydrogen-bonding arrangement. In the last decade the number of publications where CD spectroscopy has been used to study G4-DNAs, is extremely high. However, with very few exceptions, these investigations use an empirical interpretation of CD spectra. In this interpretation two basic types of CD spectra have been associated to a single specific difference in the features of the strand folding, i.e. the relative orientation of the strands, “parallel” (all strands have the same 5′ to 3′ orientation) or “antiparallel”. Different examples taken from the literature where the empirical interpretation is not followed or is meaningless are presented and discussed. Furthermore, the case of quadruplexes formed by monomeric guanosine derivatives, where there is no strand connecting the adjacent quartets and the definition parallel/antiparallel strands cannot apply, will be discussed. The different spectral features observed for different G-quadruplexes is rationalised in terms of chromophores responsible for the electronic transitions. A simplified exciton coupling approach or more refined QM calculations allow to interpret the different CD features in terms of different stacking orientation (head-to-tail, head-to-head, tail-to-tail) between adjacent G-quartets irrespectively of the relative orientation of the stands (parallel/antiparallel).
256 citations
TL;DR: The complexation behavior of a series of paraquats with pillar[5]arene (P5A) host has been comprehensively investigated, showing the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior.
Abstract: The complexation behavior of a series of paraquats (G1·2PF6–G5·2PF6) and bis(pyridinium) derivatives (G6·2PF6–G14·2PF6) with pillar[5]arene (P5A) host has been comprehensively investigated by 1H NMR, ESI mass and UV-vis absorption spectroscopy. It is found that P5A forms 2 : 1 external complexes with N,N′-dialkyl-4,4′-bipyridiniums (G1–G4·2PF6); while it forms 1 : 1 pseudorotaxane-type inclusion complexes with methylene [–(CH2)n–] linked bis(pyridinium) derivatives possessing appropriate chain lengths (n = 3–6, G7–G10·2PF6). Host–guest association constants in dimethyl sulfoxide (DMSO) were determined, indicating G7–G10·2PF6 axles form stable [2]pseudorotaxanes with P5A wheel in this very high polarity solvent and 1,4-bis(pyridinium)butane (G8·2PF6) was the most suitable axle unit. Meanwhile, the nature of the substituents attached to 1,4-bis(pyridinium)butane dramatically affects the molecular recognition behavior. The introduction of pyridyls (G13·2PF6) increases not only the Ka value (4.5 × 102→7.4 × 102 M−1), but also the charge transfer (CT) absorption (colorless→yellow). Furthermore, the solvent effects have also been investigated, showing they significantly influence the association strength during the course of host–guest complexation. Particularly, the Ka value of P5A–G13·2PF6 in 1 : 1 (v:v) acetone-d6/DMSO-d6 is enhanced by a factor of 7.3 compared with pure DMSO-d6 (7.4 × 102→5.4 × 103 M−1).
249 citations
TL;DR: This perspective article summarizes progress in this research area until June 2010 inioselective syntheses of 1,4,5-trisubstituted 1,2,3-triazoles.
Abstract: Regioselective syntheses of 1,4,5-trisubstituted 1,2,3-triazoles were accomplished by three different strategies, relying on (i) the interception of stoichiometrically formed 5-cuprated-1,2,3-triazoles, (ii) the use of stoichiometrically functionalized alkynes or (iii) catalytic C–H bond functionalizations. This perspective article summarizes progress in this research area until June 2010.
225 citations
TL;DR: The main focus of this perspective lies in the discussion of the recent mechanistic theories and supporting experimental evidences that have been put forth in an attempt to advance the understanding of the factors affecting chemical glycosylation.
Abstract: The main focus of this perspective lies in the discussion of the recent mechanistic theories and supporting experimental evidences that have been put forth in an attempt to advance our understanding of the factors affecting chemical glycosylation.
222 citations
TL;DR: A review of the progress made in tackling glycosidase inhibition, which has widespread application in a number of diseases, in particular by examining those inhibitors that may mimic the transition state.
Abstract: Glycoside hydrolases, the enzymes responsible for hydrolysis of the glycosidic bond in di-, oligo- and polysaccharides, and glycoconjugates, are ubiquitous in Nature and fundamental to existence. The extreme stability of the glycosidic bond has meant these enzymes have evolved into highly proficient catalysts, with an estimated 1017 fold rate enhancement over the uncatalysed reaction. Such rate enhancements mean that enzymes bind the substrate at the transition state with extraordinary affinity; the dissociation constant for the transition state is predicted to be 10−22 M. Inhibition of glycoside hydrolases has widespread application in the treatment of viral infections, such as influenza and HIV, lysosomal storage disorders, cancer and diabetes. If inhibitors are designed to mimic the transition state, it should be possible to harness some of the transition state affinity, resulting in highly potent and specific drugs. Here we examine a number of glycosidase inhibitors which have been developed over the past half century, either by Nature or synthetically by man. A number of criteria have been proposed to ascertain which of these inhibitors are true transition state mimics, but these features have only be critically investigated in a very few cases.
TL;DR: This review presents a general overview of the potential approaches to activate enzymes for diverse enzymatic processes and biotransformations in ILs to dramatically increase the solvent tolerance, enhance activity as well as stability, and improve enantioselectivity.
Abstract: As environmentally benign “green” solvents, room temperature ionic liquids (ILs) have been used as solvents or (co)solvents in biocatalytic reactions and processes for a decade. The technological utility of enzymes can be enhanced greatly by their use in ionic liquids (ILs) rather than in conventional organic solvents or in their natural aqueous reaction media. In fact, the combination of green properties and unique tailor-made physicochemical properties make ILs excellent non-aqueous solvents for enzymatic catalysis with numerous advantages over other solvents, including high conversion rates, high selectivity, better enzyme stability, as well as better recoverability and recyclability. However, in many cases, particularly in hydrophilic ILs, enzymes show relative instability and/or lower activity compared with conventional solvents. To improve the enzyme activity as well as stability in ILs, various attempts have been made by modifying the form of the enzymes. Examples are enzyme immobilization onto support materials via adsorption or multipoint attachment, lyophilization in the presence of stabilizing agents, chemical modification with stabilizing agents, formation of cross-linked enzyme aggregates, pretreatment with polar organic solvents or enzymes combined with suitable surfactants to form microemulsions. The use of these enzyme preparations in ILs can dramatically increase the solvent tolerance, enhance activity as well as stability, and improve enantioselectivity. This perspective highlights a number of pronounced strategies being used successfully for activation and stabilization of enzymes in non-aqueous ILs media. This review is not intended to be comprehensive, but rather to present a general overview of the potential approaches to activate enzymes for diverse enzymatic processes and biotransformations in ILs.
TL;DR: Receptor 1 is the first ever example where a single molecular probe is able to show imine (C=N) isomerization inhibition along with twisted intramolecular charge transfer (TICT) in combinatorial fashion.
Abstract: A new fluorescent probe (5-[(4-diethylamino-2-hydroxy-benzylidene)-amino]-1H-pyrimidine-2, 4-dione) (Receptor 1) has been synthesized by the Schiff base condensation of 5-aminouracil with 4-(diethylamino)salicylaldehyde. The receptor 1 exhibits high selectively for Al(3+) in DMSO as well as in aqueous solution even in the presence of biologically relevant cations such as Na(+), K(+), Ca(2+), Mg(2+), Pb(2+) and several transition metal ions. The lowest detection limit for the receptor 1 was found to be 1.62 × 10(-10) M with its linear response towards Al(3+) in the concentration range of 1.75 × 10(-9) to 3.3 × 10(-8) M in DMSO. Receptor 1 is the first ever example where a single molecular probe is able to show imine (C=N) isomerization inhibition along with twisted intramolecular charge transfer (TICT) in combinatorial fashion.
TL;DR: This review deals mainly with supramolecular and nano-chemical approaches to the problem of selectivity enhancement in various functionalizations of C-H compounds.
Abstract: The selectivity is an extremely important characteristic of a chemical reaction. This review deals mainly with supramolecular and nano-chemical approaches to the problem of selectivity enhancement in various functionalizations of C–H compounds. Enzyme mimics is a very fruitful method to achieve the predominant formation of desirable products and isomers. By obstructing the approach of certain C–H bonds of a substrate to the active catalytic centre we simultaneously increase the relative reactivity of other fragments. This can be done by creating steric hindrance around the active centre. Spatial restrictions can be made if we place the catalyst into a nano-cavity. We can achieve discrimination in reactivity of different C–H bonds if we allow certain fragments to approach closely the active centre. In order to do this chemists use coordination of the catalyst to some groups of the substrate with the participation of relatively strong binding (chelate control) or relatively weak forces (molecular recognition).
TL;DR: This work reviews recent developments and applications of aldolase-type organocatalytic direct transformations in aqueous media without addition of organic solvent.
Abstract: We review recent developments and applications of aldolase-type organocatalytic direct transformations in aqueous media without addition of organic solvent.
TL;DR: Impregnated copper on magnetite is a versatile, inexpensive and simple catalyst for the selective multicomponent reaction of terminal alkynes, aldehydes and secondary amines to give the corresponding propargylamines with excellent yields.
Abstract: Impregnated copper on magnetite is a versatile, inexpensive and simple catalyst for the selective multicomponent reaction of terminal alkynes, aldehydes and secondary amines to give the corresponding propargylamines with excellent yields. The catalyst can be easily recovered and reused by using a simple magnet. The process could be repeated up to ten times without losing its activity.
TL;DR: This article highlights some recent developments of this synthetic approach for the preparation of functionalized indole derivatives that may react with a large variety of nucleophilic reagents.
Abstract: Elimination of suitable leaving groups from 3-substituted indoles under basic or acidic conditions readily provides alkylideneindolenine intermediates that may react with a large variety of nucleophilic reagents. This article highlights some recent developments of this synthetic approach for the preparation of functionalized indole derivatives.
TL;DR: The easy functionalization of tags and solid supports with the vinyl sulfone function is a valuable tool in omic sciences that allows their coupling with the amine and thiol groups present in the proteogenic residues of proteins, in mild and green conditions compatible with their biological function.
Abstract: The easy functionalization of tags and solid supports with the vinyl sulfone function is a valuable tool in omic sciences that allows their coupling with the amine and thiol groups present in the proteogenic residues of proteins, in mild and green conditions compatible with their biological function.
TL;DR: The synthesis and evaluation of a novel Schiff-base fluorescent probe L for detection of Al(3+) and fluorescent spectra changes and microscopy images show that indicator L is highly selective for Al( 3+) not only in abiotic systems but also in living cells.
Abstract: The synthesis and evaluation of a novel Schiff-base fluorescent probe L for detection of Al3+ are described. The structure of L was determined by X-ray and other spectroscopic data. The fluorescent spectra changes and microscopy images show that indicator L is highly selective for Al3+ not only in abiotic systems but also in living cells. Other metal ions failed to respond. The new probe could be used as an efficient tool for Al3+ monitoring in the environment and biological systems.
TL;DR: The usefulness of radical stability values for the rationalization of successful (and not so successful) synthetic radical reactions as well as the potential design of new radical reactions are highlighted.
Abstract: The thermodynamic stability of carbon-centered radicals may be defined in quantitative terms using the hydrogen transfer reaction shown in eqn (a). The stability values obtained in this way for substituted systems may be understood as the stabilizing or destabilizing influence of substituents on the neighboring radical center. This approach can be easily adapted to oxygen- or sulfur-centered radicals as expressed in eqn (b). The stability values obtained in this way do not only serve as a quantitative basis for the discussion of substituent effects, but also allow for quantitative estimates of reaction energies for hydrogen transfer reactions. These occur as key steps in a multitude of synthetically useful radical-chain processes in apolar solution, in enzyme-mediated non-chain processes in biological systems, and in the oxidative degradation of a variety of biomolecules. The review will highlight the usefulness of radical stability values for the rationalization of successful (and not so successful) synthetic radical reactions as well as the potential design of new radical reactions.
TL;DR: Two novel "turn-on" fluorescent probes with perylene tetracarboxylic diimide (PDI) as the fluorophore and two different di-(2-picolyl)-amine groups as the metal ion receptor were successfully synthesized with satisfactory yields, suggesting that PDIs are favorable fluorophores for a "turn on" fluorescence probe for paramagnetic transition metal ions because of their high oxidation potential.
Abstract: Two novel “turn-on” fluorescent probes with perylene tetracarboxylic diimide (PDI) as the fluorophore and two different di-(2-picolyl)-amine (DPA) groups as the metal ion receptor (PDI-1 and PDI-2) were successfully synthesized with satisfactory yields. PDI-1 exhibited high selectivity toward Ni2+ in the presence of various other metal cations including Zn2+, Cd2+ and Cu2+ which were expected to interfere significantly. A 1 : 2 stoichiometry was found for the complex formed by PDI-1 and Ni2+ by a Job's plot and by non-linear least square fitting of the fluorescence titration curves. By introducing an extra diamino ethylene group between DPA and the phenyl bridge, the receptor was modified and the high selectivity of the sensor toward Ni2+ shifted to Fe3+. The enhancement factor of the fluorescence response of PDI-2 to Fe3+ was as high as 138. The binding behavior of the receptors in these two compounds is affected significantly by the PDI fluorophores. Most interestingly, both Ni2+ and Fe3+ are paramagnetic metal ions, which are known as fluorescence quenchers and are rarely targeted with “turn-on” fluorescence probes. This result suggests that PDIs are favorable fluorophores for a “turn-on” fluorescence probe for paramagnetic transition metal ions because of their high oxidation potential.
TL;DR: Comparing formation of all possible bipyrimidine photoproducts upon UVA irradiation of cells, purified genomic DNA and dA(20):dT(20) oligonucleotide duplex shows that UVA-induced cyclobutane pyrimidine dimers are formed via a direct photochemical mechanism, without mediation of a cellular photosensitiser.
Abstract: The carcinogenic action of UVA radiation is commonly attributed to DNA oxidation mediated by endogenous photosensitisers Yet, it was recently shown that cyclobutane pyrimidine dimers (CPD), well known for their involvement in UVB genotoxicity, are produced in larger yield than oxidative lesions in UVA-irradiated cells and skin In the present work, we gathered mechanistic information on this photoreaction by comparing formation of all possible bipyrimidine photoproducts upon UVA irradiation of cells, purified genomic DNA and dA20:dT20 oligonucleotide duplex We observed that the distribution of photoproducts, characterized by the sole formation of CPD and the absence of (6-4) photoproducts was similar in the three types of samples The CPD involving two thymines represented 90% of the amount of photoproducts Moreover, the yields of formation of the DNA lesions were similar in cells and isolated DNA In addition, the effect of the wavelength of the incident photons was found to be the same in isolated DNA and cells This set of data shows that UVA-induced cyclobutane pyrimidine dimers are formed via a direct photochemical mechanism, without mediation of a cellular photosensitiser This is possible because the double-stranded structure increases the capacity of DNA bases to absorb UVA photons, as evidenced in the case of the oligomer dA20:dT20 These results emphasize the need to consider UVA in the carcinogenic effects of sunlight An efficient photoprotection is needed that can only be complete by completely blocking incident photons, rather than by systemic approaches such as antioxidant supplementation
TL;DR: This account summarizes the newest naphthylmethyl (NAP) ether-mediated IAD as well as all the types of mediations for stereospecific construction of various 1,2-cis linkages, not only for beta-mannopyranoside, but also for other linkages almost without exception, including beta-L-rhamnoside.
Abstract: Methodology toward the stereoselective 1,2-cis glycoside linkage using intramolecular aglycon delivery (IAD) has been extensively developed. In the last two decades, progress has been made using various mixed acetal linkages and a number of glycosyl donor moieties to develop novel IAD strategies, mainly based on formation of acetal linkages. This account summarizes the newest naphthylmethyl (NAP) ether-mediated IAD as well as all the types of mediations for stereospecific construction of various 1,2-cis linkages, not only for β-mannopyranoside, but also for other linkages almost without exception, including β-L-rhamnoside.
TL;DR: This contribution will highlight the relatively few examples of stereoselective transformations organocatalyzed by chiral phosphine oxides, discussing the different proposed reaction mechanisms and identifying topics for future investigation in what can be most certainly defined as an "Emerging Area".
Abstract: The design and synthesis of new chiral Lewis bases is a field of extraordinary activity; in this context, while N-oxides derived from both N-heterocyclic systems and aliphatic amines have found widespread applications in organocatalysis, quite surprisingly phosphine oxides have been used less frequently. This contribution will highlight the relatively few examples of stereoselective transformations organocatalyzed by chiral phosphine oxides, discussing the different proposed reaction mechanisms and identifying topics for future investigation in what can be most certainly defined as an “Emerging Area”.
TL;DR: A new probe for Cu(2+) based on the Cu (2+)- induced reversible ring-opening mechanism of the rhodamine spirolactam displayed a highly selective and sensitive "turn-on" fluorescent and colorimetric response toward Cu( 2+).
Abstract: A new probe for Cu2+ based on the Cu2+- induced reversible ring-opening mechanism of the rhodamine spirolactam was described. It displayed a highly selective and sensitive “turn-on” fluorescent and colorimetric response toward Cu2+.
TL;DR: The cobalt(ii)-complex catalyzes efficiently the intramolecular C-N and C-O cross-couplings of Z-N'-(2-halophenyl)-N-phenylamidines and N-(2-bromophenyl)benzamides to afford the corresponding substituted benzimidazoles and benzoxazoles in the presence of K(2)CO(3) at moderate temperature.
Abstract: Cobalt(II)-complex catalyzes efficiently the intramolecular C–N and C–O cross-couplings of Z-N′-(2-halophenyl)-N-phenylamidines and N-(2-bromophenyl)benzamides to afford the corresponding substituted benzimidazoles and benzoxazoles in the presence of K2CO3 at moderate temperature. The protocol is general, air stable and affords the products selectively in moderate to high yield.
TL;DR: A novel structural class of phenazine derivatives, the dermacozines, which exhibited moderate cytotoxic activity against leukaemia cell line K562 with IC(50) values of 9 and 7 microM, respectively, while the highest radical scavenger activity was observed for der Macozine C (3) with an IC( 50) value of 8.4 microM.
Abstract: Dermacoccus abyssi sp. nov., strains MT1.1 and MT1.2 are actinomycetes isolated from Mariana Trench sediment at a depth of 10898 m. Fermentation using ISP2 and 410 media, respectively, lead to production of seven new oxidized and reduced phenazine-type pigments, dermacozines A–G (1–7), together with the known phenazine-1-carboxylic acid (8) and phenazine-1,6-dicarboxylic acid (9). Extensive use was made of 1D and 2D-NMR data, and high resolution MS to determine the structures of the compounds. To confirm the structure of the most complex pentacyclic analogue (5) we made use of electronic structure calculations to compare experimental and theoretical UV-Vis spectra, which confirmed a novel structural class of phenazine derivatives, the dermacozines. The absolute stereochemistry of dermacozine D (4) was determined as S by a combination of CD spectroscopy and electronic structure calculations. Dermacozines F (6) and G (7) exhibited moderate cytotoxic activity against leukaemia cell line K562 with IC50 values of 9 and 7 μM, respectively, while the highest radical scavenger activity was observed for dermacozine C (3) with an IC50 value of 8.4 μM.
TL;DR: A new fluorescent turn-on probe for the rapid optical sensing of thiols has been designed and synthesized that displays high on/off signal ratios and high selectivity towardsThiols.
Abstract: A new fluorescent turn-on probe for the rapid optical sensing of thiols has been designed and synthesized. The probe displays high on/off signal ratios and high selectivity towards thiols. The potential of the probe as a biosensor for thiols was demonstrated by imaging of thiols in living cells.
TL;DR: A new bifunctional cinchona alkaloid-based phosphinamide catalyst 7 could promote the Strecker reaction of isatins derived ketimine with TMSCN in up to 74% ee.
Abstract: The direct α-cyanoamination of isatins using TMSCN has been developed, which is carried out in methanol without any catalyst. A new bifunctional cinchona alkaloid-based phosphinamide catalyst 7 could promote the Strecker reaction of isatins derived ketimine with TMSCN in up to 74% ee.
TL;DR: A new flow procedure for the preparation of arylsulfonyl chlorides from aniline starting materials is described, which is safe, easily scalable and less labour intensive than the corresponding batch method.
Abstract: A new flow procedure for the preparation of arylsulfonyl chlorides from aniline starting materials is described. The reaction conditions are mild, requiring no added acid and are amenable to continuous flow processing, in a safe, easily scalable and less labour intensive way than the corresponding batch method.