From marine sponge-associated fungus Hamigera avellanea, thirteen secondary metabolies including a pair of undescribed alkaloid enantiomers (+)-hamiavemin A (4S) (+)-1 and (-)-hamiavemin A (4R) (-)-1. Compound 1 was enantiomers resolved by the Chiralpak AS-3 column, using a n-hexane/isopropanol mobile phase. Their structures were determined based on extensive analyses of HR-ESI-MS, 1D and 2D NMR spectra. The absolute configuration of (+)-1 and (-)-1 were assigned tentatively by ECD calculations. Among the isolates, compound 6 showed strongest antibacterial activity against Enterococcus faecalis, Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella enterica, and Candida albicans with the MIC values of 2, 2, 16, 32, 64, and 16 μg/mL, respectively, which were stronger than that of the positive control compound, kanamycin (MIC values ranging from 4 to 128 μg/mL). In addition, compounds 1, 2, and 9 showed moderate cytotoxic activity against three cancer cell lines, HepG2, A549, and MCF-7 with the IC50 values ranging from 55.35±1.70 to 83.02±2.85 mg/mL
Monthly Archives: September 2023
Cross‐Electrophile Coupling between Two Different Tosylates Enabled by Nickel/Palladium Cooperative Catalysis
A cross-electrophile coupling reaction of gem-difluoroalkenyl tosylate with α-CF3 benzyl tosylate is presented. This protocol is the first example of cross-electrophile coupling between two different tosylates by Pd/Ni cooperative catalysis.
Abstract
Cross-electrophile coupling reactions are efficient for the construction of carbon-carbon bonds under relatively mild conditions, and hence widely used for making new molecules. Among various electrophiles, the cross-electrophile coupling reaction between two different tosylates has been rarely studied. Herein, we present a cross-electrophile coupling of gem-difluoroalkenyl tosylate (C(sp2)−OTs) and α-CF3 benzyl tosylate (C(sp3)−OTs) by nickel/palladium cooperative catalysis. Mechanistic investigation indicated that the activation of C(sp2)−OTs bond and C(sp3)−OTs bond was facilitated by nickel and palladium respectively.
B−N Co‐Doped Biphenylene as a Metal‐Free Cathode Catalyst for Li−O2 Batteries: a Computational Study
B−N co-doped biphenylene is proposed as a promising metal-free cathode catalyst for Li−O2 batteries, based on density functional theory calculations. Specially, the modeling results reveal that strengthening the Li−O bond reduces the overpotential during the discharge process, and that a moderate adsorption energy of *Li2O2 facilitates the charge process.
Abstract
Lithium-oxygen batteries (LOBs) meet the growing demand for long-distance transportation over electric vehicles but face challenges because of the lack of high-performance cathode catalysts. Herein, using density functional theory calculations, we report a unique graphene allotrope, biphenylene, of which the doping structures exhibit great potential as metal-free catalysts for LOBs. Our modeling results demonstrate that the biphenylene nanosheets retain metallic properties after B doping, N doping, or B−N co-doping. Compared with the pristine biphenylene, the catalytic activity of the doped biphenylene is greatly improved due to charge redistributions. Notably, the overpotentials of the B−N co-doped biphenylene are as low as 0.19 and 0.18 V for the discharge and charge processes, respectively. Based on the electronic structure and bonding analysis, we identify two factors, i. e., Li−O bond strength and *Li2O2 adsorption energy, that can influence the Li−O2 electrochemical reactions. This study not only proposes a promising cathode catalyst but also provides insights into optimizing cathode catalysts for LOBs.
Palladium‐Catalyzed Enantioselective Hydrofunctionalization of Alkenes: Recent Advances
Asymmetric hydrofunctionalization of alkenes represents a powerful method to obtain valuable enantioenriched molecules from cheap and readily available materials. In this review, the recent advances in Palladium catalyzed asymmetric hydrofunctionalization of alkenes covering mainly contributions over the past decade are summarized. The remained challenges and opportunities in this field are also discussed.
Abstract
Palladium-catalyzed asymmetric hydrofunctionalization of alkenes is one of the most powerful and straightforward methods to forge a new C−H bond and a new C−X (X=C, N, O, F, Si etc) bond, which provides an efficient way to obtain valuable enantioenriched molecules from cheap and readily available feedstocks. Catalytic asymmetric hydrofunctionalization of simple alkenes is challenging but still highly sought after. This review will mainly focus on the recent advances in Palladium catalyzed asymmetric hydrofunctionalization of alkenes over the past decade, including hydroamination, hydrooxygenation, hydrofluorination, hydrosilylation, hydroarylation, hydroalkenylation and hydrocarbonylation.
Radical Dearomatising Spirocyclisation of Benzisoxazole‐Tethered Ynones
The synthesis of densely functionalised spirocyclic products through a radical dearomative spirocyclisation chain mechanism is described. The spirocyclic products were converted into other spirocyclic scaffolds through a two-step ring expansion sequence.
Abstract
The dearomative spirocyclisation of benzisoxazoles through a radical chain mechanism is described. Densely functionalised spirocycles were prepared in high yields by reacting benzisoxazole-tethered ynones with aryl thiols in 1,2-dichloroethane (DCE) at 60 °C. The identification of stabilising three-electron interactions was key to the development of this new radical cascade reaction. The obtained spirocyclic products were converted into other spirocyclic scaffolds through a two-step hydrogenolysis-cyclisation sequence.
Structural and Chemical Properties of NiOx Thin Films: Oxygen Vacancy Formation in O2 Atmosphere
The formation and properties of oxygen vacancies on thin NiOx films were investigated in situ at elevated temperatures and high oxygen pressures. Due to charge redistribution and altered bond lengths of the atoms surrounding the oxygen vacancies, they appear as distinct spectral features in O1s and O K-edge spectra, clearly distinguishable from all other peaks.
Abstract
NiOx films on Si(111) were put in contact with oxygen at elevated temperatures. During heating and cooling in oxygen atmosphere Near Ambient Pressure (NAP)-XPS and -XAS and work function (WF) measurements reveal the creation and replenishing of oxygen vacancies in dependence of temperature. Oxygen vacancies manifest themselves as a distinct O1s feature at 528.9 eV on the low binding energy side of the main NiO peak as well as by a distinct deviation of the Ni2p3/2 spectral features from the typical NiO spectra. DFT calculations reveal that the presence of oxygen vacancies leads to a charge redistribution and altered bond lengths of the atoms surrounding the vacancies causing the observed spectral changes. Furthermore, we observed that a broadening of the lowest energy peak in the O K-edge spectra can be attributed to oxygen vacancies. In the presence of oxygen vacancies, the WF is lowered by 0.1 eV.
Design, Synthesis of (±)‐Millpuline A, and Biological Evaluation for the Lung Cell Protective Effects through SRC
We report a visible-light-induced intermolecular [2+2] photocycloaddition reaction based on flavonoids to synthesize (±)-millpuline A and 20 derivatives (B1–B20), which could be constructed to address the problems of low yield, poor physicochemical properties, and lack of target definition in total synthesis of complex natural products.
Abstract
In this study, a visible-light-induced intermolecular [2+2] photocycloaddition reaction based on flavonoids was constructed to address the problems of low yield, poor physicochemical properties, and lack of target definition in total synthesis of (±)-millpuline A whose bioactivity remains unknown. As a result, 20 derivatives were synthesized for bioactivity evaluation. Consequently, lung cell protective effects of (±)-millpuline A and compound B13 a were revealed for the first time and the crucial role of stereoconfiguration of the cyclobutane moiety in their protective effects against NNK in normal lung cells was demonstrated. Moreover, through target prediction and experimental verification in MLE-12 cells, SRC was determined to be the target of (±)-millpuline A regarding its protective effect in NNK-induced lung cell injury. Results from RT-Q-PCR and HTRF experiments verified that (±)-millpuline A could repress SRC activity through a transcriptional mechanism but not acting as an inhibitor to directly bind to and thereby inhibit SRC protein. The results in this paper are informative for the further development of visible light-catalyzed cycloaddition of flavonoids and lay a scientific foundation for understanding the bioactivity and underlying mechanism of (±)-millpuline A and other structurally similar natural skeletons.
A Detailed Insight into the Effects of Morphologies of Cerium Oxide on Fenton‐like Reactions for Different Applications
In the context of the Fenton-like reaction involving cerium oxide, cubic CeO2 primarily facilitate the decomposition of H2O2 into reactive oxygen species, resulting in significant damage to lung adenocarcinoma cells. In contrast, rod-like CeO2 predominantly engage in the complexation of H2O2, leading to the formation of peroxides, thereby demonstrating a pronounced capability of organic dye degradation.
Abstract
As an exceptional Fenton-like reagent, cerium oxide (CeO2) finds applications in biomedical science and organic pollutants treatment. The Fenton-like reaction catalyzed by CeO2 typically encompasses two distinct processes: one resembling the classical Fenton reaction, wherein cerium (Ce3+) triggers the decomposition of hydrogen peroxide (H2O2) to yield reactive oxygen species (ROS), and the other involves the complexation of H2O2 on the Ce3+ surface, leading to the formation of peroxides. However, the influence of diverse CeO2 morphologies on these two reaction pathways has not been comprehensively explored. In this study, CeO2 exhibiting three typical morphologies, rods, cubes, and spheres, were prepared. The generation of ROS and peroxides was evaluated using the 3,3,5,5-tetramethylbenzidine (TMB) oxidation reaction and the reduction current of H2O2, respectively. Moreover, the impacts of pH variations and CeO2/H2O2 concentrations on the production and conversion of these two reaction products were investigated. To corroborate the distinctions between the resultant products and their applicability, apoptosis assays and acid orange 7 (AO7) degradation analyses were performed. Notably, CeO2 rods exhibited the highest proportion of Ce3+, predominantly engaging in complexation with H2O2 to foster peroxide formation, thereby facilitating the robust degradation of AO7. However, the generated peroxides appeared to occupy Ce3+ sites, thereby impeding the H2O2 decomposition process. Conversely, Ce3+ species on the surface of CeO2 cubes were primarily involved in H2O2 decomposition, leading to heightened ROS production, and thus showcasing substantial potential for damaging A549 tumor cells. It is worth noting that the ability of these Ce3+ species to form peroxides through complexation with H2O2 was comparatively reduced. In summation, this study sheds light on the intricate interplay between distinct CeO2 morphologies and their divergent impacts on Fenton-like reactions. These findings expand our comprehension of the influences on its reactivity of CeO2 morphologies and open new insights for applications in diverse domains, from organic dye degradation to tumor therapy.
Unveiling the Noncovalent Interaction of Thiazol‐2‐ylidene and Its Derivatives as N‐heterocyclic Carbene with Different Proton Donor Molecules
A systematic noncovalent interaction study of thiazole-2-ylidene derivatives with five different proton donor molecules. This computational investigation will contribute towards designing of an efficient catalyst for synthetic chemists and drug designing for medicinal chemistry.
Abstract
The importance of noncovalent interaction has gained attention in various domains covering drug and novel catalyst design. The present study mainly characterizes the role of hydrogen bond (H-bond) and other intermolecular interactions in different (1 : 1) complex analogues formed between the N-aryl-thiazol-2-ylidene (YR) and five proton donor (HX) molecules. The analysis of the singlet-triplet energy gap ( ) confirmed the stability of the singlet state for this class of N-aryl-thiazol-2-ylidenes than the triplet state. The interaction energy values of the YR-HX complexes follow the order: YR-NH3<YR-HCN<YR-H2O<YR-MeOH<YR-HF. In addition, substituting the H-atom of the N−H bond with bulky groups (−R) leads to an increase in the interaction energy of the YR-HX complexes. Hence, it was found that the replacement of N-atom in N-heterocyclic carbene (NHC) by S-atom forming N-aryl-thiazol-2-ylidene results in comparable intermolecular interactions with proton donor molecules similar to imidazole-2-ylidene (NHC). The current study enlightened the role of noncovalent interactions in carbene complexes with proton donor molecules. We hope that our work on carbene chemistry will pave the way for its application in the designing and synthesis of efficient catalysts.
Dose Addition Models Accurately Predict the Subacute Effects of a Mixture of Perfluorooctane Sulfonate (PFOS) and Perfluorooctanoic Acid (PFOA) on Japanese Quail (Coturnix japonica) Chick Mortality.
Abstract
Biomonitoring data have consistently demonstrated that fish, wildlife, and humans are exposed to multiple per- and polyfluoroalkyl substances (PFAS) in drinking water and foods. Despite ubiquitous exposure to mixtures of PFAS, there is a lack of in vivo PFAS mixture research that addresses if these chemicals act in a cumulative, dose-additive manner or if they behave independently. For this reason, there is a critical need for mixtures studies designed to evaluate the cumulative toxicity and potential chemical interactions to support the assessment of human and ecological risks as well as define appropriate regulatory actions. The primary objective of this communication was to evaluate the previously published Japanese quail chick mortality concentration-response data for PFOS and PFOA and the mixture of PFOS+PFOA and use statistical modeling to determine if the effects of the mixtures were accurately predicted by either dose- (DA) or response addition (RA) modeling. In addition, we wanted to compare different DA models to determine if one model produced more accurate predictions than the others. Results support the hypothesis of cumulative effects on shared endpoints from PFOA and PFOS co-exposure and dose additive approaches for predictive estimates of cumulative effects. Given the limited number of in vivo studies that have been executed with enough individual PFAS and PFAS mixture concentration-response data to test the hypothesis of DA for PFAS mixtures, this reanalysis of the data is an important contribution to our understanding of how PFAS mixtures act. The analysis will provide support for regulatory agencies as they begin to implement PFAS cumulative hazard assessments in higher vertebrates.