Probing the Electron Accepting Ability of Phosphaphenalenes.

Phosphaphenalenes, extended π conjugates with the incorporation of phosphorus, are attractive avenues towards molecular materials for the applications in organic electronics, but their electron accepting ability have not been investigated. Herein we present systematic studies on the reductive behavior of a representative phosphaphenalene and its oxide by chemical and electrochemical methods. The chemical reduction of the phosphaphenalene by alkali metals reveals the facile P-C bond cleavage to form phosphaphenalenide anion, which functions as a transfer block for structure modification on the phosphorus atom. In contrast, the pentavalent P-oxide reacts with one or two equivalents of elemental sodium to form stable radical anion and dianion salts, respectively.

[4+1] cyclization of α-diazo esters and mesoionic N-heterocyclic olefins.

Prompted by the recent stepwise mechanistic proposal for the Huisgen [3+2] cycloaddition reaction between enamine and α-diazo ester, where the nucleophilic addition of the enamine carbon onto the terminal nitrogen of diazo ester is crucial, we examined the possible use of N-heterocyclic olefins (NHOs) as highly electron-rich dipolarophiles in these reactions. The mesoionic NHOs derived from 1,2,3-triazoles undergo fast [4+1] cycloaddition to give 3-(triazolium-4-yl)-(3H)-pyrazol-4-olates at room temperature. The reaction mechanism has been explored through experimental and DFT computational studies.

Recent advances of mesoionic N-heterocyclic olefins.

This Perspective article highlights the recent development of mesoionic N-heterocyclic olefins (mNHOs), where the exo-cyclic olefinic carbon is not bonded to strongly electron-withdrawing groups. The unquenched basicity and nucleophilicity of the exo-cyclic olefinic carbon make mNHOs strong σ-donors and enable unique reactivity patterns.

Analysis on oral medication rules of traditional Chinese medicine prescriptions for prevention of COVID-19.

OBJECTIVE: To analyze the medication rules of traditional Chinese medicine (TCM) preventive oral prescriptions for COVID-19. METHODS: The preventive oral prescriptions for COVID-19 published by national and provincial health and wellness committees, administrations of TCM, medical institutions at all levels, medical masters and Chinese medicine experts were collected to establish a database, manual screening was carried out according to the inclusion and exclusion criteria, and frequency statistics, association rule analysis. The mutual information method, entropy hierarchical clustering and other methods were improved through Excel and the TCM inheritance auxiliary platform V2.5 to mine the rules and characteristics of medication. RESULTS: The selected 157 prescriptions contained a total of 130 TCMs. The top five TCMs with the highest use frequency were Glycyrrhizae Radix et Rhizoma (86), Astragali Radix (80), Lonicerea Japonicae Flos (70), Atractylodis Macrocephalae Rhizoma (62), Saposhnikoviae Radix (60). In accordance with TCM efficacy classification, most of them were medicines for qi-tonifying (279), followed by medicines for clearing heat and drying dampness (163), dispelling pathogenic wind-cold (126), resolving dampness (111), as well as dispelling pathogenic wind-heat (99). The characteristics of four-natures of the selected medicines are as follows: most of them were cold (59), followed by warm (38) and mild (21). In terms of five-taste, most of them were sweet (26) and acrid-and-bitter (24), followed by sweet-and-bitter (20), bitter (20) and acrid (15). For the meridian attribution, the five-zang organs and six-fu organs were all involved, most of them attributed to lung meridian (80), followed by stomach meridian (57) and spleen meridian (40). Based on association rule analysis, 12 commonly used medicine combinations with two or three TCMs were found. The commonly used medicinal pairs included Astragali Radix and Saposhnikoviae Radix (51), Astragali Radix and Atractylodis Macrocephalae Rhizoma (46), Atractylodis Macrocephalae Rhizoma and Saposhnikoviae Radix (43), Astragali Radix and Atractylodis Macrocephalae Rhizoma and Saposhnikoviae Radix (38), Forsythiae Fructus and Astragali Radix (37), and so on. In addition, 14 core combinations of medicines were obtained by complex system entropy cluster analysis, on this basis, six new prescriptions were screened out based on unsupervised entropy hierarchical clustering analysis. According to The Catalogue of Edible Traditional Chinese Medicinal Materials, Traditional Chinese Medicinal Materials for Health Food, and New Resources of Food published by National Health Commission of the People's Republic of China, there are 35 species belonging to the group of edible traditional Chinese medicinal materials, 20 species belonging to the group of new resources of food, 31 species belonging to the group of traditional Chinese medicinal materials for health food, 19.11% of the preventive oral prescriptions for COVID-19 were composed of the medicines belonging to the above three groups. Besides, there are 11 toxic species, and 24.84% of the preventive oral prescriptions for COVID-19 contained toxic TCMs. CONCLUSION: We found that invigorating qi and resolving dampness were the main treatment used to prevent for COVID-19, combined with the methods for strengthening vital energy and eliminating pathogenic factors. Most of the preventive oral prescriptions for COVID-19 were treated in lung, spleen and stomach meridians. In the process of selecting prescriptions and using TCMs to prevent for COVID-19, the safety of preventive medicines was also emphasized. And the theory of "Preventive Treatment of Disease" was embodied in these preventive oral prescriptions for COVID-19. For the prescriptions containing toxic TCMs, special attention should be paid to their safety in clinical application.

Dioxygenation of unprotected mesoionic N-heterocyclic olefins.

We report the dioxygenation of mesoionic N-heterocyclic olefins (mNHOs) using molecular dioxygen. For 1,2,3-triazole-derived mNHOs possessing a vinyl proton and at least one acidic C-H group, they are oxidized into the corresponding triazolium benzoate salts, whereas those without vinyl proton or an acidic C-H group are oxidized into triazolium oxide and ketones/aldehydes.

Constructing fused N-heterocycles from unprotected mesoionic N-heterocyclic olefins and organic azides via diazo transfer.

Mesoionic N-heterocyclic olefins (mNHOs) were first reported last year and their reactivity remains largely unexplored. Herein we report the reaction of unprotected mNHOs and organic azides as a novel synthetic route to a variety of pyrazolo[3,4-d][1,2,3]triazoles, an important structural motif in drug candidates and energetic materials. The only byproduct aniline can be easily recycled and converted back to the starting organic azide, in compliance with the green chemistry principle. The reaction mechanism has been explored through experimental and computational studies.

[2Fe-2S] Cluster Supported by Redox-Active o-Phenylenediamide Ligands and Its Application toward Dinitrogen Reduction.

As prevalent cofactors in living organisms, iron-sulfur clusters participate in not only the electron-transfer processes but also the biosynthesis of other cofactors. Many synthetic iron-sulfur clusters have been used in model studies, aiming to mimic their biological functions and to gain mechanistic insight into the related biological systems. The smallest [2Fe-2S] clusters are typically used for one-electron processes because of their limited capacity. Our group is interested in functionalizing small iron-sulfur clusters with redox-active ligands to enhance their electron storage capacity, because such functionalized clusters can potentially mediate multielectron chemical transformations. Herein we report the synthesis, structural characterization, and catalytic activity of a diferric [2Fe-2S] cluster functionalized with two o-phenylenediamide ligands. The electrochemical and chemical reductions of such a cluster revealed rich redox chemistry. The functionalized diferric cluster can store up to four electrons reversibly, where the first two reduction events are ligand-based and the remainder metal-based. The diferric [2Fe-2S] cluster displays catalytic activity toward silylation of dinitrogen, affording up to 88 equiv of the amine product per iron center.

Cysestermerol A, a rare stilbene sestermer with significant hypoglycemic activities from Cynodon dactylon.

Cysestermerol A (1), a rare and new stilbene sestermer, was isolated from the whole herb of Cynodon dactylon. The planar and relative structures of 1 were elucidated based on HRESIMS, one- and two-dimensional NMR analyses, and its absolute configuration was further established by electronic circular dichroism calculations. Compound 1 obviously increased the glucose consumption in HepG2 cells equivalent to the positive control rosiglitazone and markedly inhibited the activity of α-glucosidase in vitro.

Syntheses and characterizations of iron complexes of bulky o-phenylenediamide ligand.

We report the syntheses of a family of tetrahedral iron complexes bearing a bulky redox active o-phenylenediamide ligand. The electronic structures of these complexes have been investigated by Mössbauer spectroscopy, magnetic susceptibility measurements, and X-ray crystallography.

Iron N-heterocyclic carbene complexes in homogeneous catalysis.

The development of homogeneous iron catalysts has been a prolific research field in recent years. Many catalytic reactions are no longer limited to noble metals. The use of N-heterocyclic carbenes (NHCs) as ancillary ligands has made substantial impact in noble metal catalysis and also started to gain popularity in iron catalysis in recent years. This review article surveys the recent literature on Fe-NHC-catalyzed chemical reactions, including C-C bond formation, reduction, and oxidation reactions.

Anti-Inflammatory and Anti-Apoptotic Effects of Stybenpropol A on Human Umbilical Vein Endothelial Cells.

Inflammation is a key mediator in the progression of atherosclerosis (AS). Benzoinum, a resin secreted from the bark of Styrax tonkinensis, has been widely used as a form of traditional Chinese medicine in clinical settings to enhance cardiovascular function, but the active components of the resin responsible for those pharmaceutical effects remain unclear. To better clarify these components, a new phenylpropane derivative termed stybenpropol A was isolated from benzoinum and characterized via comprehensive spectra a nalysis. We further assessed how this phenylpropane derivative affected treatment of human umbilical vein endothelial cells (HUVECs) with tumor necrosis factor-α (TNF-α). Our results revealed that stybenpropol A reduced soluble intercellular cell adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), interleukin-8 (IL-8), and interleukin-1ß (IL-1ß) expression by ELISA, inhibited apoptosis, and accelerated nitric oxide (NO) release in TNF-α-treated HUVECs. We further found that stybenpropol A decreased VCAM-1, ICAM-1, Bax, and caspase-9 protein levels, and increased the protein levels of Bcl-2, IKK-ß, and IκB-α. This study identified a new, natural phenylpropane derivative of benzoinum, and is the first to reveal its cytoprotective effects in the context of TNF-α-treated HUVECs via regulation of the NF-κB and caspase-9 signaling pathways.

Constructing reactive Fe and Co complexes from isolated picolyl-functionalized N-heterocyclic carbenes.

We report the isolation of free picolyl-functionalized N-heterocyclic carbenes (NHCs), which serve as versatile precursors to access low coordinate iron and cobalt complexes. The reactivities of these new iron and cobalt complexes towards catalytic hydrosilylation of ketones have also been explored. For example, low loadings (0.05-1 mol%) of a four-coordinate iron complex bearing two deprotonated picolyl-NHC ligands can effect the fast catalytic reduction of ketones using the inexpensive industrial byproduct polymethylhydrosiloxane (PMHS) as the reductant at ambient temperature.

[Effect of Xinling Wan in treatment of stable angina pectoris: a randomized, double-blinded, placebo parallel-controlled, multicenter trial].

To evaluate the effectiveness and safety of Xinling Wan on patients with stable angina pectoris, a randomized, double-blinded, placebo parallel-controlled, multicenter clinical trial was conducted. A total of 232 subjects were enrolled and randomly divided into experiment group and placebo group. The experiment group was treated with Xinling Wan (two pills each time, three times daily) for 4 weeks, and the placebo group was treated with placebo. The effectiveness evaluation showed that Xinling Wan could significantly increase the total duration of treadmill exercise among patients with stable angina pectoris. FAS analysis showed that the difference value of the total exercise duration was between experiment group (72.11±139.32) s and placebo group (31.25±108.32) s. Xinling Wan could remarkably increase the total effective rate of angina pectoris symptom score, and the analysis showed that the total effective rate was 78.95% in experiment group and 42.61% in placebo group. The reduction of nitroglycerin dose was (2.45±2.41) tablets in experiment group and (0.50±2.24) tablets in placebo group on the basis of FAS analysis. The decrease of symptom integral was (4.68±3.49) in experiment group and (3.19±3.31) in placebo group based on FAS analysis. Besides, Xinling Wan could decrease the weekly attack time and the duration of angina pectoris. PPS analysis results were similar to those of FAS analysis. In conclusion, Xinling Wan has an obvious therapeutic effect in treating stable angina pectoris, with a good safety and a low incidence of adverse event and adverse reaction in experiment group.

Unusual Rearrangement of an N-Donor-Functionalized N-Heterocyclic Carbene Ligand on Group 8 Metals.

We report an unexpected rearrangement of a deprotonated picolyl-functionalized N-heterocyclic carbene (NHC) ligand from N,C-chelate to N,N-chelate in three-legged piano-stool Fe(II) and Ru(II) complexes. The reaction mechanism has been explored for one of the Fe(II) complexes. Experimental and computational studies suggest an unusual intermediate featuring a four-membered chelate ring, where the NHC and the α-carbon of one of the N-substituents coordinate to the Fe(II) center. A possible Fe-alkylidene intermediate has also been predicted by computations.

Reactivity of Fe and Ru Complexes of Picolyl-Substituted N-Heterocyclic Carbene Ligand: Diverse Coordination Modes and Small Molecule Binding.

Complexes [MClCp*(HL)] (1[Fe]/1[Ru]) (where HL = 1-mesityl-3-(pyridin-2-ylmethyl)imidazol-2-ylidene) were synthesized from the reaction of in situ generated HL ligand and [FeClCp*(TMEDA)] (where TMEDA is N,N,N',N'-tetramethylethylenediamine) or [RuClCp*]4, respectively. The deprotonation of 1[Fe]/1[Ru] with 1 equiv of LiHMDS led to cyclometalation through the o-Me of the mesityl group, forming [MCp*(L-κC,κC',κN)] 2[Fe]/2[Ru]. The coordinatively unsaturated compounds [MCp*(HL)]BPh4 3[Fe]/3[Ru] were prepared from 1[Fe]/1[Ru] and halide scavenger NaBPh4. Complex 3[Ru] showed agostic interactions between the o-Me group of the mesityl moiety and the metal center in solution and the solid state. When the vacant coordination site of 3[Fe]/3[Ru] is occupied by CO, the resulting [MCp*(CO)(HL)]BPh4 4[Fe]/4[Ru] can be deprotonated with 1 equiv of KHMDS at the pyridylic position to afford complexes [MCp*L'(CO)] 5[Fe]/5[Ru], where the L'- ligand chelates to the metal center through the nitrogen donor atom of the dearomatized pyridine ring and the carbene carbon. Complex 2[Fe] reacted rapidly with CO to afford the simple ligand substitution product [FeCp*(L-κC,κC')(CO)] 6[Fe], where the L- acts as a bidentate chelating ligand through the carbene carbon and benzylic carbon. Under the same condition, the reaction of 2[Ru] with CO forms [RuCp*L″(CO)] 7[Ru], where the L″- ligand (an isomer of L- and L'-) chelates to the metal center through the carbene carbon and a pyridyl carbon. Complexes 3[Fe]/3[Ru] reversibly bind dinitrogen to form [MCp*(HL)(N2)]BPh4 8[Fe]/8[Ru]. 3[Ru] reversibly binds dihydrogen to give [MCp*(H2)(HL)]BPh4 9[Ru], while no reaction was observed between 3[Fe] and H2. The reaction of 3[Ru] with dioxygen led to the isolation of a stable side-on O2 complex [RuCp*(HL)(O2)]BPh4 10[Ru], while the reaction of 3[Fe] with dioxygen led to an intractable mixture of products.

Iron-Catalyzed gem-Specific Dimerization of Terminal Alkynes.

We report a gem-specific homo- and cross-dimerization of terminal alkynes catalyzed by a well-defined iron(II) complex containing Cp* and picolyl N-heterocyclic carbene (NHC) ligands, and featuring a piano-stool structure. This catalytic system requires no additives and is compatible with a broad range of substrates, including those with polar functional groups such as NH and OH.

Zwitterionic indenylammonium with carbon-centred reactivity towards reversible CO2 binding and catalytic reduction.

We report the synthesis and characterization of a zwitterionic indenylammonium compound and its carbon-centred reactivity towards reversible CO2 binding at ambient temperature through its formal insertion into a C-H bond as well as the catalytic hydroboration of CO2 to methanol derivatives.

Iron complexes of a bidentate picolyl-NHC ligand: synthesis, structure and reactivity.

The synthesis, structure and reactivity of bidentate picolyl N-heterocyclic carbene (NHC) iron compounds were studied. Compounds [FeBr(HL)2]Br (1), [FeBr(HL)(HMDS)] (2) and [FeBr2(HL)] (3) (HL = 1-mesityl-3-(pyridin-2-ylmethyl)imidazol-1-ylidene, HMDS = hexamethyldisilazide) were prepared from H2LBr with suitable amounts of Fe(HMDS)2 or in situ prepared [Fe(HMDS)Br]. The deprotonation of 1 with 2 eq. of LiHMDS gave [FeL2] (4), featuring dearomatized pyridine moieties with exocyclic C-C double bonds. The protonation of 4 with 2 eq. of PPh3·HBr results in the formation of 1. Attempted deprotonation of 3 using benzyl Grignard as the base resulted in transmetalation products [FeBnBr(HL)] (5) and [FeBn2(HL)] (6). Exposure of 6 to CO resulted in the formation of diamagnetic compound [Fe(CO)3(HL)] (7) and dibenzyl ketone. Prolonged exposure of 7 to CO with heating induces pyridine dissociation, affording [Fe(CO)4(HL-κC)] (8). Treatment of compound 6 with an equimolar amount of p-methoxybenzyl bromide yielded homo- and cross-coupling products.