A wheat resistosome defines common principles of immune receptor channels.

Plant intracellular nucleotide-binding leucine-rich repeat receptors (NLRs) detect pathogen effectors to trigger immune responses1. Indirect recognition of a pathogen effector by the dicotyledonous Arabidopsis thaliana coiled-coil domain containing NLR (CNL) ZAR1 induces the formation of a large hetero-oligomeric protein complex, termed the ZAR1 resistosome, which functions as a calcium channel required for ZAR1-mediated immunity2-4. Whether the resistosome and channel activities are conserved among plant CNLs remains unknown. Here we report the cryo-electron microscopy structure of the wheat CNL Sr355 in complex with the effector AvrSr356 of the wheat stem rust pathogen. Direct effector binding to the leucine-rich repeats of Sr35 results in the formation of a pentameric Sr35-AvrSr35 complex, which we term the Sr35 resistosome. Wheat Sr35 and Arabidopsis ZAR1 resistosomes bear striking structural similarities, including an arginine cluster in the leucine-rich repeats domain not previously recognized as conserved, which co-occurs and forms intramolecular interactions with the 'EDVID' motif in the coiled-coil domain. Electrophysiological measurements show that the Sr35 resistosome exhibits non-selective cation channel activity. These structural insights allowed us to generate new variants of closely related wheat and barley orphan NLRs that recognize AvrSr35. Our data support the evolutionary conservation of CNL resistosomes in plants and demonstrate proof of principle for structure-based engineering of NLRs for crop improvement.

A receptor-like protein acts as a specificity switch for the regulation of stomatal development.

Stomata are microscopic openings that allow for the exchange of gases between plants and the environment. In Arabidopsis, stomatal patterning is specified by the ERECTA family (ERf) receptor kinases (RKs), the receptor-like protein (RLP) TOO MANY MOUTHS (TMM), and EPIDERMAL PATTERNING FACTOR (EPF) peptides. Here we show that TMM and ER or ER-LIKE1 (ERL1) form constitutive complexes, which recognize EPF1 and EPF2, but the single ERfs do not. TMM interaction with ERL1 creates a binding pocket for recognition of EPF1 and EPF2, indicating that the constitutive TMM-ERf complexes function as the receptors of EPF1 and EPF2. EPFL9 competes with EPF1 and EPF2 for binding to the ERf-TMM complex. EPFL4 and EPFL6, however, are recognized by the single ERfs without the requirement of TMM. In contrast to EPF1,2, the interaction of EPFL4,6 with an ERf is greatly reduced in the presence of TMM. Taken together, our data demonstrate that TMM dictates the specificity of ERfs for the perception of different EPFs, thus functioning as a specificity switch for the regulation of the activities of ERfs.

Investigation of steric hindrance effect on the interactions between four alkaloids and HSA by isothermal titration calorimetry and molecular docking.

The binding of four alkaloids with human serum albumin (HSA) was investigated by isothermal titration calorimetry (ITC), spectroscopy and molecular docking techniques. The findings demonstrated that theophylline or caffeine can bind to HAS, respectively. The number of binding sites and binding constants are obtained. The binding mode is a static quenching process. The effects of steric hindrance, temperature, salt concentration and buffer solution on the binding indicated that theophylline and HSA have higher binding affinity than caffeine. The fluorescence and ITC results showed that the interaction between HSA and theophylline or caffeine is an entropy-driven spontaneous exothermic process. The hydrophobic force was the primary driving factor. The experimental results were consistent with the molecular docking data. Based on the molecular structures of the four alkaloids, steric hindrance might be a major factor in the binding between HSA and these four alkaloids. This study elucidates the mechanism of interactions between four alkaloids and HSA.

Iodine-Mediated δ-Amination of sp3 C-H Bonds.

We present a direct δ-amination reaction of sp3 C-H bonds, employing molecular iodine (I2) as the sole oxidant under transition-metal-free conditions. This remote C-H functionalization approach is operationally simple and provides facile, efficient access to pyrrolidines and related heterocyclic derivatives from readily accessible substrates.

TMSOTf-Catalyzed Reactions of N-Arylynamides with Sulfilimines To Construct 2-Aminoindoles and α-Arylated Amidines.

Here, we disclose an efficient TMSOTf-catalyzed C-H annulation of aryl-terminated N-arylynamides with sulfilimines, leading to the practical assembly of various valuable 2-aminoindoles in generally moderate to excellent yields with a broad range of functional groups, while nonaryl terminated N-arylynamides undergo TMSOTf-catalyzed aminative arylation with sulfilimines providing α-arylated amidines.

Synthesis of 2,2-difunctionalized 2H-azirines via I2-mediated annulation of enamines.

Various 2,2-difunctionalized 2H-azirines were synthesized via I2-mediated annulation reactions of readily accessible enamines in the presence of nitrogen or non-nitrogen nucleophiles. The features of the present synthesis process also include no use of transition metals, simple operation, mild reaction conditions, a broad substrate scope, and gram-scale synthesis.

Brønsted acid catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones.

Herein, we describe a novel metal-free Brønsted acid-catalyzed Ficini [2 + 2] cycloaddition of ynamides with enones under mild reaction conditions, leading to the formation of various cyclobutenamides in generally good to excellent yields within short reaction times. This work represents the first example of ynamides involved in a nonmetal-catalyzed [2 + 2] cycloaddition with enones.

Redox-Regulated Synthetic Channels: Enabling Reversible Ion Transport by Modulating the Ion-Permeation Pathway.

Natural redox-regulated channel proteins often utilize disulfide bonds as redox sensors for adaptive regulation of channel conformations in response to diverse physiological environments. In this study, we developed novel synthetic ion channels capable of reversibly switching their ion-transport capabilities by incorporating multiple disulfide bonds into artificial systems. X-ray structural analysis and electrophysiological experiments demonstrated that these disulfide-bridged molecules possess well-defined tubular cavities and can be efficiently inserted into lipid bilayers to form artificial ion channels. More importantly, the disulfide bonds in these molecules serve as redox-tunable switches to regulate the formation and disruption of ion-permeation pathways, thereby achieving a transition in the transmembrane transport process between the ON and OFF states.

4'-Modified Nucleosides for Antiviral Drug Discovery: Achievements and Perspectives.

Modified nucleosides show therapeutic promise for antiviral therapies. However, issues including the emergence of drug resistance, toxicity, and coinfections have posed new challenges for nucleoside-based antiviral drug discovery, particularly in the era of the coronavirus disease 2019 (COVID-19) pandemic. Chemical manipulation could impact the antiviral potency, safety, and drug resistance of nucleosides. Generally, modified nucleosides are difficult to recognize by intracellular important enzymes as substrates and thus exhibit low toxicity. 4'-Modified nucleosides represent an important subclass of modified nucleosides for antiviral therapies. To prevent the occurrence of drug resistance, 4'-modified nucleosides should have 3'-OH, which should also be chemically unreactive for proviral DNA biosynthesis. The absence of 3'-OH may explain the occurrence of drug resistance for censavudine. The introduction of 4'-substituents improves enzymatic and acidic stability and makes the nucleosides more lipophilic, thus improving cell permeability and bioavailability. Steric hindrance between the 4'-substituent and 3'-OH changes the furanose conformation to the 3'-endo type, in which the oxygen lone pair on the furanose ring could not form an oxocarbonium ion for glycolysis. Currently, seven 4'-modified nucleoside drug candidates such as azvudine (also known as FNC), islatravir, censavudine, balapiravir, lumicitabine, AL-335, and 4-azidothymidine have progressed into clinical stages for treating viral infections. Of note, FNC was officially approved by NMPA in July 2021 for use in adult patients with high HIV-1 virus loads (nos. H20210035 and H20210036), providing an alternative therapeutic for patients with HIV-1. The long-term cellular retention of FNC suggests its potential as a long-lasting pre-exposure prophylaxis (PrEP) agent for preventing HIV-1 infection. Mechanistically, FNC not only inhibited HIV-1 reverse transcription and replication but also restored A3G expression in peripheral blood CD4+ T cells in HIV-1 patients receiving FNC. The 4'-azido group in azvudine stabilizes the 3'-C-endo (north) conformation by steric effects and the formation of an intramolecular hydrogen bond with the 3'-OH group, thus decreasing the nucleophilicity of 3'-OH. The north conformation may also enhance the phosphorylation efficiency of FNC by cellular kinases. Encouragingly, FNC, islatravir, and balapiravir show promise for the treatment of coronaviruses, of which FNC has advanced to phase 3 clinical trials in different countries to treat patients with COVID-19 (clinical trial numbers: NCT04668235 and NCT04425772). FNC cured the COVID-19 disease in almost all patients and showed better therapeutic efficacy than remdesivir. In this Account, we provide an overview of 4'-modified nucleoside analogs in clinical stages for antiviral therapies, highlighting the drug discovery strategies, structure-activity relationship studies, and preclinical/clinical studies and also give our perspectives on nucleoside-based antiviral drug discovery.

Enantioselective Synthesis of Chiral Organosilicon Compounds by Organocatalytic Asymmetric Conjugate Addition of Boronic Acids to ß-Silyl-α,ß-Unsaturated Ketones.

Herein, we report (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-catalyzed enantioselective conjugate addition of organic boronic acids to ß-silyl-α,ß-unsaturated ketones, furnishing moderate to excellent yields of the corresponding ß-silyl carbonyl compounds with stereogenic centers in excellent enantioselectivities (up to 98% ee). Moreover, the catalytic system features mild reaction conditions, high efficiency, broad substrate scope, and easy scale-up.

Synthesis of Quinazolinone-Fused Tetrahydroisoquinolines and Related Polycyclic Scaffolds by Iodine-Mediated sp3 C-H Amination.

An iodine-mediated intramolecular sp3 C-H amination reaction producing quinazolinone-fused polycyclic skeletons from 2-aminobenzamide precursors is reported. This reaction does not use transition metals, has a broad substrate scope, and can be used on a gram scale. Under the optimal reaction conditions, a variety of quinazolinone-fused tetrahydroisoquinolines and derivatives of Rutaecarpine were synthesized from readily accessible compounds. The reaction proceeds well with crude 2-aminobenzamide derivatives, allowing for the synthesis of the products from simple 2-aminobenzoic acids and tetrahydroisoquinolines without purification of the 2-aminobenzamide intermediates. Preliminary biological experiments have identified Cereblon (CRBN) inhibitory activity and relevant anti-myeloma medicinal properties in some of these polycyclic products.

Iodine-Mediated α-C-H Amination of Carbonyl Compounds via Nitrogen-Directed Oxidative Umpolung.

A new synthetic strategy for direct C(sp3)-H amination of carbonyl compounds at their α-carbon has been established employing molecular iodine and nitrogen-directed oxidative umpolung. In this transformation, iodine acts not only as an iodinating reagent but also as a Lewis acid catalyst, and both the nitrogen-containing moiety and the carbonyl group in the substrate play important roles. This synthetic approach is applicable to a broad variety of carbonyl substrates, including esters, ketones, and amides. Its features also include no requirement for transition metals, mild reaction conditions, short reaction times, and gram-scale synthesis.

Chiral-Boron-Complex-Catalyzed Asymmetric [3 + 2] Cycloaddition of ß-Trifluoromethyl α,ß-Unsaturated Ketones with N,N'-Cyclic Azomethine Imines.

The (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-boron-complex-catalyzed asymmetric 1,3-dipolar cycloaddition of ß-trifluoromethyl α,ß-unsaturated ketone with N,N'-cyclic azomethine imines was developed to afford N,N'-bicyclic pyrazolidine derivatives bearing a stereogenic carbon center containing CF3 motifs in high yields with excellent diastereo- and enantioselectivities (up to >20:1 dr, and >99% ee). This catalytic system features mild reaction conditions, high efficiency, and a broad substrate scope.

Highly Enantioselective Chiral Diol-Catalyzed Conjugate Addition of Boronic Acids to α,ß-Unsaturated Trifluoromethyl Ketones.

The (R)-3,3'-(3,5-(CF3)2-C6H3)2-BINOL-catalyzed enantioselective conjugate addition of organic boronic acids to α,ß-unsaturated 1,1,1-trifluoromethyl ketones affords corresponding addition products bearing a stereogenic center at the ß-position in moderate to high yields and excellent enantioselectivities (up to 99% ee), without any 1,2-addition product formation. Moreover, this catalytic protocol features mild reaction conditions, a broad substrate scope, suitability for alkenylboronic acids and (hetero)arylboronic acids, and easy scale-up.

Copper-Catalyzed Synthesis of N-Fused Quinolines via C(sp3)-H Activation-Radical Addition-Cyclization Cascade.

A novel copper-catalyzed cyclization reaction for the synthesis of pyrazolo[1,5-a]quinoline, triazolo[1,5-a]quinoline, and pyrrolo[1,2-a]quinoline derivatives is described. The process is initiated by di-tert-butyl peroxide-mediated C(sp3)-H activation to generate the α-functionalized radical, which supervenes a cascade radical addition/cyclization sequence to access the N-fused quinolines in good yields with broad functional group tolerance.

Synthesis of novel oxazol-5-one derivatives containing chiral trifluoromethyl and isoxazole moieties as potent antitumor agents and the mechanism investigation.

In this study, a series of novel oxazol-5-one derivatives containing a chiral trifluoromethyl and isoxazole moiety were synthesized and evaluated for cytotoxic activities. Among them, 5t was the most effective compound against HepG2 liver cancer cells with an IC50 of 1.8 µM. 5t inhibited cell proliferation, migration, invasion, and induced cell cycle arrest and apoptosis in vitro. Nevertheless, the potential anti-hepatocellular carcinoma (HCC) target and mechanism of 5t were unclear. This work aimed to seek the molecular target of 5t against HCC and investigate its mechanism. Liquid chromatography tandem-mass spectrometry was used to identify peroxiredoxin 1(PRDX1) as a possible target of 5t. Cellular thermal shift assay, drug affinity responsive target stability, and molecular docking provided conclusive evidence that 5t targeted PRDX1 and inhibited its enzymatic activity. 5t augmented the level of reactive oxygen species (ROS) and led to ROS-dependent DNA damage, endoplasmic reticulum stress, mitochondrial dysfunction, and apoptosis in HepG2 cells. Silencing PRDX1 also resulted in ROS-mediated apoptosis in HepG2 cells. In vivo, 5t inhibited mouse tumor growth by increasing oxidative stress. Briefly, our studies revealed that compound 5t targeted PRDX1 through a ROS-dependent mechanism, highlighting the future development of compound 5t as a novel therapeutic drug for HCC.

Enantioselective Conjugate Addition of Boronic Acids to α,ß-Unsaturated 2-Acyl Imidazoles Catalyzed by Chiral Diols.

Herein, we report the enantioselective conjugate addition of organic boronic acids to α,ß-unsaturated 2-acyl imidazoles using (R)-3,3'-I2-BINOL as the catalyst. The catalytic system shows high efficiency and tolerance to alkenylboronic acids and heteroarylboronic acids. The corresponding Michael addition products were obtained in moderate to excellent yields and with moderate to excellent enantioselectivities (up to 97% ee). A gram-scale reaction was also conducted, and the desired product was obtained in high yield with no erosion in enantioselectivity. Finally, the synthetic utility of the methodology was demonstrated by transforming the 2-acyl imidazole moiety to the corresponding aldehyde, carboxylic acid, ester, and amide derivatives.

Synthesis of 2-Aminopyrroles Via Metal-Free Annulation of Ynamides with 2H-Azirines.

A novel metal-free annulation of ynamides with 2H-azirines catalyzed by BF3·Et2O is described, leading to the construction of polysubstituted 2-aminopyrroles in a facile, flexible, and atom-economical way. This synthetic strategy proceeds with efficiency, broad substrate scope, and short reaction time under mild reaction conditions. Furthermore, the obtained annulation products could be modified to generate diverse 2-iminopyrrole frameworks in high yields.

Metal-free hydroalkoxylation of ynesulfonamides with alcohols.

Efforts for developing a convenient and expeditious method for synthesizing alkoxy-substituted enamides via nucleophilic addition of alcohols to ynesulfonamides are described. This sequence is completely regioselective and highly stereoselective, and leads to the hydroalkoxylation products in high yields under mild reaction conditions.

Highly Regio- and Enantioselective Hydrosilylation of gem-Difluoroalkenes by Nickel Catalysis.

The synthesis of small organic molecules with a difluoromethylated stereocenter is particularly attractive in drug discovery. Herein, we have developed an efficient method for the direct generation of difluoromethylated stereocenters through Ni0 -catalyzed regio- and enantioselective hydrosilylation of gem-difluoroalkenes. The reaction also represents the enantioselective construction of carbon(sp3 )-silicon bonds with nickel catalysis, which provides an atom- and step-economical synthesis route of high-value optically active α-difluoromethylsilanes. This protocol features readily available starting materials and commercial chiral catalysis, broad substrates spanning a range of functional groups with high yield (up to 99 % yield) and excellent enantioselectivity (up to 96 % ee). The enantioenriched products undergo a variety of stereospecific transformations. Preliminary mechanistic studies were performed.