Electrocatalytic Synthesis of Essential Amino Acids from Nitric Oxide Using Atomically Dispersed Fe on N-doped Carbon

How to transfer industrial exhaust gases of nitrogen oxides into high-values product is significantly important and challenging. Herein, we demonstrate an innovative method for artificial synthesis of essential α-amino acids from nitric oxide (NO) by reacting with α-keto acids through electrocatalytic process with atomically dispersed Fe supported on N-doped carbon matrix (AD-Fe/NC) as the catalyst. A yield of valine with 32.1 μmol mg_cat⁻¹ is delivered at −0.6 V vs. reversible hydrogen electrode, corresponding a selectivity of 11.3 %. In situ X-ray absorption fine structure and synchrotron radiation infrared spectroscopy analyses show that NO as nitrogen source converted to hydroxylamine that promptly nucleophilic attacked on the electrophilic carbon center of α-keto acid to form oxime and subsequent reductive hydrogenation occurred on the way to amino acid. Over 6 kinds of α-amino acids have been successfully synthesized and gaseous nitrogen source can be also replaced by liquid nitrogen source (NO₃⁻). Our findings not only provide a creative method for converting nitrogen oxides into high-valued products, which is of epoch-making significance towards artificial synthesis of amino acids, but also benefit in deploying near-zero-emission technologies for global environmental and economic development.     

Enantioselective Synthesis of Biscyclopropanes Using Alkynes as Dicarbene Equivalents

Chiral biscyclopropanes are an important skeleton in many bioactive molecules. However, there are few routes to synthesize these molecules with high stereoselectivity due to the nature of multiple stereocenters. Herein, we report the first example of Rh₂(II)-catalyzed enantioselective synthesis of bicyclopropanes with alkynes as dicarbene equivalents. The bicyclopropanes with 4–5 vicinal stereocenters and 2–3 all-carbon quaternary centers were constructed in excellent stereoselectivity. This protocol features high efficiency and excellent functional group tolerance. Moreover, the protocol was also extended to the cascaded cyclopropanation/cyclopropenation with excellent stereoselectivities. In these processes, both sp-carbons of alkyne were converted into stereogenic sp³-carbons. Experimental and density functional theory (DFT) calculations revealed that the cooperative weak hydrogen bonds between the substrates and the dirhodium catalyst may play key roles in this reaction.     

On-Surface Synthesis and Real-Space Visualization of Aromatic P3N3

On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of unstable or unconventional molecules, which could not be obtained via traditional synthetic methods. A case in point is the on-surface synthesis of the structurally elusive cyclotriphosphazene (P₃N₃), an inorganic aromatic analogue of benzene. Here, we report the preparation of this fleetingly existing species on Cu(111) and Au(111) surfaces at 5.2 K through molecular manipulation with unprecedented precision, i.e., voltage pulse-induced sextuple dechlorination of an ultra-small (about 6 Å) hexachlorophosphazene P₃N₃Cl₆ precursor by the tip of a scanning probe microscope. Real-space atomic-level imaging of cyclotriphosphazene reveals its planar D_3h-symmetric ring structure. Furthermore, this demasking strategy has been expanded to generate cyclotriphosphazene from a hexaazide precursor P₃N₂₁ via a different stimulation method (photolysis) for complementary measurements by matrix isolation infrared and ultraviolet spectroscopy.     

Desymmetrization of Geminal Difluoromethylenes using a Palladium/Copper/Lithium Ternary System for the Stereodivergent Synthesis of Fluorinated Amino Acids

Fluorinated amino acids and related peptides/proteins have been found widespread applications in pharmaceutical and agricultural compounds. However, strategies for introducing a C−F bond into amino acids in an enantioselective manner are still limited and no such asymmetric catalysis strategy has been reported. Herein, we have successfully developed a Pd/Cu/Li ternary system for stereodivergent synthesis of chiral fluorinated amino acids. This method involves a sequential desymmetrization of geminal difluoromethylenes and allylic substitution with amino acid Schiff bases via Pd/Li and Pd/Cu dual activation, respectively. A series of non-natural amino acids bearing a chiral allylic/benzylic fluorine motif are easily synthesized in high yields with excellent regio-, diastereo-, and enantioselectivities (up to >20 : 1 dr and >99 % ee). A density functional theory (DFT) study revealed the F−Cu interaction of the allylic substrate and the Cu catalyst significantly influence the stereoselectivity.     

Real-time Imaging of Nascent DNA in Live Cells by Monitoring the Fluorescence Lifetime of DNA-Incorporated Thiazole Orange-Modified Nucleotides

A modified 2′-deoxycytidine triphosphate derivative ( dC^TOTP ) bearing a thiazole orange moiety tethered via an oligoethylene glycol linker was designed and synthesized. The nucleotide was incorporated into DNA by DNA polymerases in vitro as well as in live cells. Upon incorporation of dC^TOTP into DNA, the thiazole orange moiety exhibited a fluorescence lifetime that differed significantly from the non-incorporated (i.e. free and non-covalently intercalated) forms of dC^TOTP . When dC^TOTP was delivered into live U-2 OS cells using a synthetic nucleoside triphosphate transporter, it allowed us to distinguish and monitor cells that were actively synthesizing DNA in real time, from the very first moments after the treatment. We anticipate that this probe could be used to study chromatin organization and dynamics.     

Azide Ionic Liquids for Safe,Green, and Highly-Efficient Azidation Reactions to Produce Azide Polymers

Azide compounds are widely used and especially, polymers bearing pendant azide groups are highly desired in numerous fields. However, harsh reaction conditions are always mandatory to achieve full azidation, causing severe side reactions and degradation of the polymers. Herein, we report the design and preparation of two azide ionic liquids (AILs) with azide anion and triethylene glycol (E₃)-containing cation, [P_444E3][N₃] and [MIM_E3][N₃]. Compared with the traditional sodium azide (NaN₃) approach, both AILs showed much higher reaction rates and functional-group tolerance. More importantly, they could act as both reagents and solvents for the quantitative azidation of various polymeric precursors under mild conditions. Theoretical simulations suggested that the outstanding performance of AILs originated from the existence of ion pairs during the reaction, and the E₃ moieties played a crucial role. Lastly, after the reaction, the AILs could be easily regenerated, presenting a safer, greener, and highly efficient synthesis route for azide polymers.     

Synthesis of nickel cobalt-codoped tin oxide nanoparticles from Psidium guajava with anticancer properties

Metal oxide nanoparticles have been found to selectively target the tumor cells while non-toxic to the normal cells. Leukemia is one of the widespread and deadly cancers in adults, as well as the most common cancer in children. Recently, the nanoparticles have evolved as a simple, economic, effective, and ecologically sound strategy among the known nanoparticle synthesis techniques. In the present study, the structural, optical, and antibacterial effects of nickel cobalt-codoped Tin oxide nanoparticles (SnNiCoO2 NPs) formulated by the green process and the anticancer potential of SnNiCoO2 NPs in Molt-4 cells have been studied. The cytotoxic potential of the NPs against Molt-4 cells was estimated by MTT assay. The ROS and MMP levels were measured using fluorescent dyes and the changes in morphology and nuclei were noted using AO/EB staining. CAT, SOD, MDA, and GSH), and Proinflammatory Cytokines (TNF-α and IL1β) were also studied. The activity of caspase-3, ?9, and ?8 levels was examined to analyze the apoptotic mechanism. The XRD patterns of SnNiCoO2 NPs revealed a tetragonal structure. The SnNiCoO2 NPs was revealed a diameter of 126 nm by the DLS study. The morphology and elemental composition were studied using FESEM and EDAX spectra. In the FT-IR study, the O-sn-O stretching band was found to be 615 and 542 cm-1. The antimicrobial potential of the SnNiCoO2 NPs was examined against S. aureus, E. coli, and C. Albicans strains. A tremendous reduction in the viability of MOLT-4 cells at concentration-dependent mode witnessed the cytotoxic potential of the formulated NPs. The augmented ROS accumulation, depletion of MMP status, depleted antioxidants, and increased proinflammatory cytokines (TNF-α and IL1β) were noted on the NPs exposed cells. Furthermore, the increased expressions of caspase-3, ?9, and ?8 was also noted in the NPs treated MOLT-4 cells. Hence, the outcomes suggest that the formulated SnNiCoO2 NPs had remarkably potent antimicrobial and anticancer properties and could potentially prove beneficial in cancer treatment. Induces mitochondrial oxidative stress with nickel–cobalt-codoped tin oxide nanoparticles from Psidium guajava, which is a potential drug candidate for the antibiotic, antifungal, and anticancer activities of plant-based nanoparticles.     

Synthesis and anti-α-glucosidase activity evaluation of betulinic acid derivatives

In this article, a series of betulinic acid derivatives (3a ～ 3u, 4a ～ 4e) were synthesized through a stepwise structure optimization and evaluated for their anti-α-glucosidase activities. All synthesized derivatives exhibited stronger anti-α-glucosidase activities (IC₅₀: 0.56 ± 0.05 ～ 3.99 ± 0.23 μM) than betulinic acid (IC₅₀: 7.21 ± 0.58 μM) and acarbose (IC₅₀: 611.45 ± 15.51 μM). Compound 3q presented the outstanding inhibitory activity (IC₅₀: 0.56 ± 0.05 μM), which was ～ 1100 time stronger than that of acarbose. Compound 3q was revealed as a reversible and noncompetitive α-glucosidase inhibitor by inhibitory mechanism assay. Fluorescence spectra, 3D fluorescence and CD spectra results showed that the interaction of compound 3q with α-glucosidase caused the conformational and secondary structure content change of α-glucosidase. Finally, the molecular docking simulated the interaction between compound 3q with α-glucosidase and the physicochemical parameter was assessed using SwissADME software.     

β-Silylacrylate as a Multipurpose Reagent in Organic Synthesis

Acrylates are well known electrophilic alkenes having multitude of applications in organic synthesis. They are very good acceptors in Michael addition reactions and are good enophile/dienophile/dipolarophile partners in cycloaddition reactions. Replacing the β-alkyl/aryl groups in acrylates by a silicon group would be interesting. In addition to the conventional reactions displayed by acrylates, β-silylacrylates (β-SAs) can show reactivity specifically related to the silicon group. Many conventional organic reactions such as hydrodimerization, organocatalytic asymmetric Michael additions, inter- and intra-molecular Diels–Alder reactions, and asymmetric 1,3-dipolar cycloadditions have been used to generate the complex chemical entities from β-SAs. Some of the reaction outcomes were vastly influenced by the silicon substituent. This review describes the practical synthesis β-SAs and their use as starting point in complex molecule generation including total synthesis of some natural products/bioactive molecules.     

Asymmetric Total Synthesis of Hasubanan Alkaloids: Periglaucines A–C,N,O-Dimethyloxostephine and Oxostephabenine

We report herein the asymmetric total synthesis of periglaucines A–C, N,O-dimethyloxostephine and oxostephabenine. The key strategies used include: 1) a Rh^I-catalyzed regio- and diastereoselective Hayashi-Miyaura reaction to connect two necessary fragments; 2) an intramolecular photoenolization/Diels–Alder (PEDA) reaction to construct the highly functionalized tricyclic core skeleton bearing a quaternary center; 3) a bio-inspired intramolecular Michael addition and transannular acetalization to generate the aza[4.4.3]propellane and the tetrahydrofuran ring.