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An efficient enantioselective synthesis of tetrahydro‐β‐carbolines (THBCs) using chiral metal‐monothiosquaramides (M–MTSQs) was planned. The in situ generated Pd/Fe‐monothiosquaramides (Pd/Fe‐MTSQs) catalysed imine reduction of dihydro‐β‐carbolines exceptionally to afford chiral THBCs with an excellent enantiomeric excess (up to 98% ee). In a catalysis study, Pd‐MTSQ 12 a (10 mol%) was found to be more efficient than Pd‐MTSQ 12 b and Fe‐MTSQs (13 a and 13 b) for enantioselective imine reduction of DHBCs 14 a–e. All the major chiral alkyl‐THBC isomers 15 a–c (90% ee, 98% ee and 95% ee, respectively) were observed with R configuration which was explained by Si face hydride attack on alkyl DHBC imines (14 a–c). Surprisingly, S configuration was perceived for the major isomers of chiral aryl‐THBCs 15 d and 15 e (95% ee and 96% ee, respectively) which was rationalized by Re face hydride attack on aryl DHBC imines (14 d and 14 e). [ABSTRACT FROM AUTHOR]

Organic halogen compounds are cornerstones of applied chemical sciences. Halogen substitution is a smart molecular design strategy adopted to influence reactivity, membrane permeability and receptor interaction. Chiral bioreceptors may restrict the stereochemical requirements in the halo‐ligand design. Straightforward (but expensive) catalyzed stereospecific halogenation has been reported. Historically, PCl5 served access to uncatalyzed stereoselective chlorination although the stereochemical outcomes were influenced by steric parameters. Nonetheless, stereochemical investigation of PCl5 reaction mechanism with carbamoyl (RCONHX) compounds has never been addressed. Herein, we provide the first comprehensive stereochemical mechanistic explanation outlining halogenation of carbamoyl compounds with PCl5; the key regioselectivity‐limiting nitrilimine intermediate (8‐Z.HCl); how substitution pattern influences regioselectivity; why oxadiazole byproduct (P1) is encountered; stereo‐electronic factors influencing the hydrazonoyl chloride (P2) production; and discovery of two stereoselectivity‐limiting parallel mechanisms (stepwise and concerted) of elimination of HCl and POCl3. DFT calculations, synthetic methodology optimization, X‐ray evidence and experimental reaction kinetics study evidence all supported the suggested mechanism proposal (Scheme 2). Finally, we provide mechanism‐inspired future recommendations for directing the reaction stereoselectivity toward elusive and stereochemically inaccessible (E)‐bis‐hydrazonoyl chlorides along with potentially pivotal applications of both (E/Z)‐stereoisomers especially in medicinal chemistry and protein modification. [ABSTRACT FROM AUTHOR]

N1‐substituted derivatives of anti‐(2R,3S)‐1,3‐diamino‐4‐phenylbutan‐2‐ol are important building blocks for the synthesis of therapeutically important molecules. We describe a simple protocol that allows transformation of N,N‐dibenzyl‐L‐phenylalaninal into such compounds in only two steps. The first step is a fully stereoselective three‐component MAC (Masked Acyl Cyanide) oxyhomologation reaction implicating different amines to give a panel of ten N,N‐dibenzyl‐O‐tert‐butyldimethylsilyl‐protected anti‐(2S,3S)‐allophenylnorstatin amides. The second step is a carbonyl‐activated hydride deprotection/reduction protocol using trimethylsilyl chloride and lithium aluminium hydride; the one‐pot two‐component system is more efficient than the alternative approach of isolating the deprotected amide intermediate before reduction. [ABSTRACT FROM AUTHOR]

A palladium‐catalyzed highly C−S‐selective Stille cross‐coupling between aryl thianthrenium salts and tri‐ or tetrasubstituted alkenyl stannanes is described. Herein, critical challenges including site‐ and chemoselectivity control are well addressed through C−H thianthrenation and C−S alkenylation, thereby providing an expedient access to stereodefined tri‐ and tetrasubstituted alkenes in a stereoretentive fashion. Indeed, the palladium‐catalyzed Stille‐alkenylation of poly(pseudo)halogenated arenes displays privileged capability to differentiate C−S over C−I, C−Br, C−Cl bonds, as well as oxygen‐based triflates (C−OTf), tosylates (C−OTs), carbamates and sulfamates under mild reaction conditions. Sequential and multiple cross‐couplings via selective C−X functionalization should be widely applicable for increasing functional molecular complexity. Modular installation of stereospecific alkene motifs into pharmaceuticals illustrated the synthetic application of the present protocol in drug discovery. [ABSTRACT FROM AUTHOR]

Bioactive dimeric (pre‐)anthraquinones are ubiquitous in nature and are found in bacteria, fungi, insects, and plants. Their biosynthesis via oxidative phenol coupling (OPC) is catalyzed by cytochrome P450 enzymes, peroxidases, or laccases. While the biocatalysis of OPC in molds (Ascomycota) is well‐known, the respective enzymes in mushroom‐forming fungi (Basidiomycota) are unknown. Here, we report on the biosynthesis of the atropisomers phlegmacin A1 and B1 of the mushroom Cortinarius odorifer. The biosynthesis of these unsymmetrically 7,10'‐homo‐coupled dihydroanthracenones was heterologously reconstituted in the mold Aspergillus niger. Methylation of the parental monomer atrochrysone to its 6‐O‐methyl ether torosachrysone by the O‐methyltransferase CoOMT1 precedes the regioselective homocoupling to phlegmacin, catalyzed by the enzyme CoUPO1 annotated as an "unspecific peroxygenase" (UPO). Our results reveal an unprecedented UPO reaction, thereby expanding the biocatalytic portfolio of oxidative phenol coupling beyond the commonly reported enzymes. The results show that Basidiomycota use peroxygenases to selectively couple aryls independently of and convergently to any other group of organisms, emphasizing the central role of OPC in natural processes. [ABSTRACT FROM AUTHOR]

AbstractSince no later than the 1970s, organic chemists have speculated on the role of glycosyl oxonium ions in chemical O-glycosylation. Such species result from the attack of ethers on glycosyl oxocarbenium ions and are invoked to explain 1,2-cis-selectivity in ether solvents. However, a systematic study to probe this phenomenon appears to be lacking in the chemical literature. Herein, we study the effects of solvent, counteranion, protecting group electron-withdrawing effects, and acceptor on O-glycosylation stereoselectivity with D-glucosyl trichloroacetimidate donors. While many of these transformations proceed with 1,2-cis-selectivity, our results suggest that glycosyl oxonium ions play minimal, if any, role in O-glycosylation. [ABSTRACT FROM AUTHOR]

In synthetic carbohydrate chemistry, the modification of glycosyl radicals pathway stands as a central area of focus. The radical‐based reactions often demonstrate remarkable compatibility with various functional groups owing to the mild initiation conditions. In particular, the identification of novel glycosyl radical precursors, combined with advanced reaction techniques, has substantially broadened the scope of glycosyl compound synthesis. Despite the presence of versatile donors, the synthesis of noble donors is still addressed as a synthetic need and challenges associated with sugar chemistry. Currently, a new class of glycosyl radical precursors has been developed which enables the production of C‐, S‐, O‐, and N‐glycosides efficiently. In this light, we highlight strategies towards bench‐stable glycosyl sulfoxides, sulphone, and sulfite donors that can enable the site‐, regio‐ and stereoselective transformation of protected or naked sugar synthons in synthetic carbohydrate chemistry. Here, this review article covers the recent developments in the selective glycosyl radical diversification such as glycosyl alkylation, arylation, alkenylation, sulfuration, C−H activation, and DNA conjugation via the bench‐stable donors along with mechanistic aspects, challenges, and future directions. [ABSTRACT FROM AUTHOR]

An approach to the synthesis of phosphoryl substituted spiro-1,3-dioxolane oxindoles was developed from the base-catalyzed reaction of various isatins with (3-hydroxyprop-1-yn-1-yl)phosphonates. It was found that various aryl-substituted and N-functionalized isatins with the formation of appropriate products with high yields and stereoselectivity when using t-BuOLi are able to react. Cytotoxic activity evaluation suggests that the most significant results in relation to the HuTu 80 cell line were shown by N-benzylated spirodioxolanes. 5-Cloro-N-unsubstituted spirooxindoles exhibit antiaggregational activity exceeding the values of acetylsalicylic acid. [ABSTRACT FROM AUTHOR]

(R)-1, 3-Butanediol (1, 3-BDO) is an important intermediate in the synthesis of aromatics, pheromones, insecticides, and beta-lactam antibiotics. The ChKRED20 is a robust NADH-dependent ketoreductase identified from Chryseobacterium sp. CA49. We obtained a ChKRED20 mutant (M12) through directed evolutionary screening of ChKRED20, the mutant with significantly improved activity to asymmetrically reduce 4-hydroxy-2-butanone (4H2B) to (R)-1, 3-BDO. So far, both ChKRED20 and its mutants have been expressed in intracellular in E. coli, the process of purification after intracellular expression is complicated, which leads to high cost. Here, we expressed M12 by constructing multicopy expression strains in P. pastoris, and the target protein yield was 302 mg/L in shake-flask fermentation and approximately 3.5 g/L in high-density fermentation. The recombinant M12 showed optimal enzyme activity at 30 °C and had high activity within a broad pH range of 6.0–8.0, and also showed high thermal stability. The recombinant M12 was further used for the reduction of 4H2B to (R)-1, 3-BDO, and 98.9% yield was achieved at 4540 mM 4H2B. The crude M12 enzyme extract was found to catalyze the bioreductive production of (R)-1, 3-BDO with excellent stereoselectivity (ee > 99%) and meet the production requirements. Our research shows that the M12 mutant can be used for the synthesis of (R)-1, 3-BDO, and the P. pastoris expression system is an ideal platform for the large-scale, low-cost preparation of ChKRED20 or its mutants, which may have applications in industrial settings. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The synthesis of N‐glycosides has received significant attention due to their crucial role in carbohydrate chemistry. Despite considerable advancements developed in the construction of N‐glycosides, methods for the stereoselective construction of 2‐deoxy‐α‐N‐glycosides are still limited. Herein, we disclosed a nickel‐catalyzed hydroamination of glycals under mild conditions. This transformation could allow for the stereoselective synthesis of an array of 2‐deoxy‐α‐N‐glycosides with excellent α‐stereoselectivity. Nickel‐catalyzed glycosylation reactions, particularly those involving anomeric C(sp3)‐metal bond formation, have proven to be an effective and stereoselective strategy for producing various N‐glycosides. Additionally, with highlight of the application of this reaction, γ‐sugar amino acid derivatives were synthesized. [ABSTRACT FROM AUTHOR]

Numerous zinc complexes based on N‐ and O‐donor Schiff‐base ligands have shown great promise in the ring‐opening polymerization (ROP) of lactides, which are cyclic dimers of lactic acid, to produce poly(lactic acid) (PLA). This is primarily because zinc is a borderline metal, making it non‐cytotoxic, inexpensive, abundant, biocompatible, and environmentally safe. Additionally, Schiff‐based ligands offer stability, stereoselectivity, desirable electronic and steric environments, and resistance to impurities. As a result, zinc complexes are easy to synthesize, colourless, have high reactivity and solubility in organic solvents, and are manageable under typical circumstances. Furthermore, these complexes are free to adopt a variety of coordination numbers since zinc does not have ligand field stabilization energy (LFSC). Zinc complexes possess high catalytic activity due to their distinctive properties, including high Lewis acidity, high electron transfer ability, stability concerning the reactive intermediate, and the ability to monitor polymerization by nuclear magnetic resonance (NMR) spectroscopy. Moreover, these complexes also have reasonable control over stereochemistry, number‐average molecular weight (Mn), and dispersity index (Ð). These advantages make it possible to produce colourless PLA with a high yield, high molecular weight, and narrow dispersity index in bulk and solvent‐based conditions. [ABSTRACT FROM AUTHOR]

Two epimeric pairs of N‐Ts‐protected cyclohexylamines that incorporate an unsaturated side‐chain at the C2 position have been prepared. Contrary to expectations, none of these underwent clean, photochemically‐induced intramolecular hydroamination reactions to give the corresponding perhydro‐indole or ‐quinoline. However, they did participate in efficient olefin cross metathesis (OCM) reactions with methyl crotonate. Three of the four acrylates so‐formed engaged in base‐promoted and completely diastereoselective, intramolecular aza‐Michael addition (cyclization) reactions to give the isomeric and C2‐substituted perhydro‐indoles or ‐quinolines with the structures of these being confirmed by single‐crystal X‐ray analyses. DFT calculations generated results consistent with the observed diastereoselectivities and the proposed transition states. Manipulation of the ester groups associated with the cyclization products allowed for their conversion, inter alia, into the corresponding n‐propyl residues and thus providing novel analogues of neurotoxic alkaloids such as pumiliotoxin C. [ABSTRACT FROM AUTHOR]

This review analyzes a development in biochemistry, enzymology and biotechnology that originally came as a surprise. Following the establishment of directed evolution of stereoselective enzymes in organic chemistry, the concept of partial or complete deconvolution of selective multi‐mutational variants was introduced. Early deconvolution experiments of stereoselective variants led to the finding that mutations can interact cooperatively or antagonistically with one another, not just additively. During the past decade, this phenomenon was shown to be general. In some studies, molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) computations were performed in order to shed light on the origin of non‐additivity at all stages of an evolutionary upward climb. Data of complete deconvolution can be used to construct unique multi‐dimensional rugged fitness pathway landscapes, which provide mechanistic insights different from traditional fitness landscapes. Along a related line, biochemists have long tested the result of introducing two point mutations in an enzyme for mechanistic reasons, followed by a comparison of the respective double mutant in so‐called double mutant cycles, which originally showed only additive effects, but more recently also uncovered cooperative and antagonistic non‐additive effects. We conclude with suggestions for future work, and call for a unified overall picture of non‐additivity and epistasis. [ABSTRACT FROM AUTHOR]

This review deals with the functionalization of double bonds carried out in the presence of a chiral catalyst exploiting the intramolecular attack to haliranium ions by nucleophilic nitrogen of amides or carbamates prepared from achiral aminoalkenes, and the C–N bonds formation leads to highly enantioenriched nonaromatic heterocycles. A range of protocols are reported, emphasizing the synthesis of many natural and biologically active products of pharmacological interest prepared according to this methodology. [ABSTRACT FROM AUTHOR]

The hydrolase-catalyzed kinetic resolution of fluorinated racemates of 3-arylcarboxylic acids is described. Hydrolysis of ethyl esters of fluorinated acids by esterases and hydrolases in all cases resulted in the formation of hydrolyzed (S)-carboxylic acids and unreacted (R)-esters in high yields and high enantiomeric purity. The influence of separation conditions on the efficiency and enantioselectivity of biocatalytic conversion was also studied. The reactions were carried out under normal conditions (stirring with a magnetic stirrer at room temperature) and microwave irradiation in the presence of hydrolases. Amano PS showed excellent selectivity and good yields in the hydrolysis of fluorinated aromatic compounds. The absolute configuration of the resulting compounds was based on biokinetic studies and the use of chiral HPLC. A molecular modeling of the kinetic resolution of carboxylic acid esters was carried out. [ABSTRACT FROM AUTHOR]

(1R,3R,5S,Z)-2-ethylidene-6,6-dimethyl-3-vinylbicyclo[3.1.1]heptane was prepared by hydrovinylation of nopadiene catalyzed by a cationic Ru complex. The structure was fully characterized by 1H- and 13C-NMR spectroscopy, including 2D-COSY and 2D-NOESY spectra, optical rotation, and combustion analysis. In contrast to the previously reported 1,2-hydrovinylation of 1-vinylcycloalkenes by this catalyst, the reaction with nopadiene proceeds by 1,4-addition of ethylene. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: The stereochemical synthesis of highly substituted Danishefsky‐type dienes remains unsolved in organic chemistry. We describe a simple and efficient approach for the stereoselective synthesis of Danishefsky‐type trisubstituted dienes from readily available propargylic esters via Pd‐catalyzed dienylation reaction through the key intermediate metallacyclobutene in a regio‐, chemo‐ and stereoselective fashion. This method facilitates a broad range of challenging trisubstituted dienes with a high level of stereocontrol. The synthetic utilities of oxygenated trisubstituted dienes have been demonstrated by the downstream chemistry, which notably undergoes Diels‐Alder reaction with a variety of electron‐deficient dienophiles to furnish multisubstituted cyclohexenes in good yields with excellent stereoselectivity. [ABSTRACT FROM AUTHOR]

Macrocyclic peptides have become increasingly important in the pharmaceutical industry. We present a detailed computational investigation of the reaction mechanism of the recently developed CyClick chemistry to selectively form imidazolidinone cyclic peptides from linear peptide aldehydes, without using catalysts or directing groups (Angew. Chem. Int. Ed. 2019, 58, 19073-19080). We conducted computational mechanistic to investigate the effects of intramolecular hydrogen bonds (IMHBs) in promoting a kinetically facile zwitterionic mechanism in CyClick of pentapeptide aldehyde AFGPA. Our DFT calculations highlighted the importance of IMHB in pre-organization of the resting state, stabilization of the zwitterion intermediate, and the control of the product stereoselectivity. Furthermore, we have also identified that the low ring strain energy promotes the CyClick of hexapeptide aldehyde AAGPFA to form a thermodynamically more stable 15+5 imidazolidinone cyclic peptide product. In contrast, large ring strain energy suppresses CyClick reactivity of tetra peptide aldehyde AFPA from forming the 9+5 imidazolidinone cyclic peptide product.

This review deals with the functionalization of double bonds carried out in the presence of a chiral catalyst exploiting the intramolecular attack to haliranium ions by nucleophilic nitrogen of amides or carbamates prepared from achiral aminoalkenes, and the C–N bonds formation leads to highly enantioenriched nonaromatic heterocycles. A range of protocols are reported, emphasizing the synthesis of many natural and biologically active products of pharmacological interest prepared according to this methodology.

The reagent system based on the combined use of Et3SiH/I2 acts as an efficient N-glycosidation promoter for the synthesis of natural and sugar-modified nucleosides. An analysis of reaction stereoselectivity in the absence of C2-positioned stereodirecting groups revealed high selectivity with six-membered substrates, depending on the nucleophilic character of the nucleobase or based on anomerization reactions. The synthetic utility of the Et3SiH/I2-mediated N-glycosidation reaction was highlighted by its use in the synthesis of the investigational drug apricitabine. [ABSTRACT FROM AUTHOR]

AbstractEne-reductase (ER) has been widely applied for asymmetrical synthesis of chiral intermediates due to its substrate promiscuity, photoexcited reactivity, and excellent property with producing two chiral centers at a time. Natural ERs often exhibit the same stereoselectivity, and they need to be engineered for opposite configuration of chiral compounds. The hydrogenation process toward activated alkenes by ERs is composed of reductive half reaction and oxidative half reaction, which are dependent upon two cofactors NAD(P)H and flavin mononucleotide. The catalytic activity of ERs will be affected by the size of the substrate, the activating strength of the electron-withdrawing groups, redox potential of cofactors, and the loop flexibility around catalytic cavity. Currently, protein engineering to ERs has been successfully employed to enhance various catalytic properties, including photoexcited asymmetric synthesis. This review summarizes the approaches to reverse the stereoselectivity and enhance catalytic activity of ERs and new applications of the engineered ERs in photobiocatalytic asymmetric synthesis, besides the discussion with the existing molecular mechanisms of mutants regarding the improved catalytic performance. [ABSTRACT FROM AUTHOR]

Carboxylesterases (CarEs) is an important detoxification enzyme system in phase Ⅰ participating in insecticides resistance. In our previous study, SlCarE054, a CarEs gene from lepidoptera class, was screened out to be upregulated in a pyrethroids and organophosphates resistant population. Its overexpression was verified in two field-collected populations of Spodoptera litura (Lepidoptera: Noctuidae) resistant to pyrethroids and organophosphates by qRT-PCR. Spatiotemporal expression results showed that SlCarE054 was highly expressed in the pupae stage and the digestive tissue midgut. To further explore its role in pyrethroids and organophosphates resistance, its metabolism activity to insecticides was determined by UPLC. Its recombinant protein showed significant metabolism activity to cyhalothrin and fenvalerate, but not to phoxim or chlorpyrifos. The metabolic activity of SlCarE054 to β -cypermethrin showed stereoselectivity, with higher metabolic activity to θ -cypermethrin than the enantiomer α -cypermethrin. The metabolite of β -cypermethrin was identified as 3-phenoxybenzaldehyde. Further modelling and docking analysis indicated that β -cypermethrin, cyhalothrin and fenvalerate could bind with the catalytic triad of the 3D structure of SlCarE054. The interaction of β -cypermethrin with SlCarE054 also showed the lowest binding energy. Our work provides evidence that SlCarE054 play roles in β -cypermethrin resistance in S. litura. [ABSTRACT FROM AUTHOR]

Context: The cyclopropane skeleton plays a significant role in bioactive molecules due to its distinctive structural properties. This has sparked keen interest and in-depth exploration in the field of stereoselective synthesis of cyclopropane derivatives. In the present study, the mechanism and the origin of stereoselectivity of diastereodivergent synthesis of cyclopropane derivatives via the catalyst-free [2 + 1]-cyclopropanation reactions of 3-diazo-N-methylindole (R1) with two types of electron-deficient olefins (R2 and R3) in both aqueous and toluene media have been studied using the DFT calculations. The findings indicate that these [2 + 1] cycloaddition reactions proceed in two stages, where the first step is not only the rate-determining step but also critically dictates the stereoselectivity of the product. The calculated diastereomeric ratios are in agreement with the experimental results. Furthermore, by utilizing non-covalent interaction (NCI) analysis and energy decomposition analysis based on molecular force fields (EDA-FF), we elucidated that the electrostatic interactions between reactant fragments in the transition state TS1s for the first step are the predominant factors determining the stereoselectivity, as opposed to the experimentally hypothesized steric hindrance and π-π stacking interactions. Methods: The geometrical structures of all minima and transition states on the potential energy surface (PES) in solvents water and toluene were fully optimized using the DFT method at the M06-2X(D3)/SMD/6–31 + G(d,p) level of theory. Single-point energy calculations were carried out based on the optimized geometries in the solution at the M06-2X(D3)/6–311 + G(d,p) level. All the DFT calculations were performed using the Gaussian 09 software. The optimized molecular structures were visualized using CYLview software. NCI analysis was performed using the Multiwfn and VMD softwares. The Multiwfn program was also used for CDFT and EDA-FF analyses. [ABSTRACT FROM AUTHOR]

Chiral epichlorohydrin (ECH) is an attractive intermediate for chiral pharmaceuticals and chemicals preparation. The asymmetric synthesis of chiral ECH using 1,3-dicholoro-2-propanol (1,3-DCP) catalyzed by a haloalcohol dehalogenase (HHDH) was considered as a feasible approach. However, the reverse ring opening reaction caused low optical purity of chiral ECH, thus severely restricts the industrial application of HHDHs. In the present study, a novel selective conformation adjustment strategy was developed with an engineered HheCPS to regulate the kinetic parameters of the forward and reverse reactions, based on site saturation mutation and molecular simulation analysis. The HheCPS mutant E85P was constructed with a markable change in the conformation of (S)-ECH in the substrate pocket and a slight impact on the interaction between 1,3-DCP and the enzyme, which resulted in the kinetic deceleration of the reverse reactions. Compared with HheCPS, the catalytic efficiency (kcat(S)-ECH/Km(S)-ECH) of the reversed reaction dropped to 0.23-fold (from 0.13 to 0.03 mM−1 s−1), while the catalytic efficiency (kcat(1,3-DCP)/Km(1,3-DCP)) of the forward reaction only reduced from 0.83 to 0.71 mM−1 s−1. With 40 mM 1,3-DCP as substrate, HheCPS E85P catalyzed the synthesis of (S)-ECH with the yield up to 55.35% and the e.e. increased from 92.54 to >99%. Our work provided an effective approach for understanding the stereoselective catalytic mechanism as well as the green manufacturing of chiral epoxides. [ABSTRACT FROM AUTHOR]

(Z)‐alkenes are useful synthons but thermodynamically less stable than their (E)‐isomers and typically more difficult to prepare. The synthesis of 1,4‐hetero‐bifunctionalized (Z)‐alkenes is particularly challenging due to the inherent regio‐ and stereoselectivity issues. Herein we demonstrate a general, chemoselective and direct synthesis of (Z)‐2‐butene‐1,4‐diol monoesters. The protocol operates within a Pd‐catalyzed decarboxylative acyloxylation regime involving vinyl ethylene carbonates (VECs) and various carboxylic acids as the reaction partners under mild and operationally attractive conditions. The newly developed process allows access to a structurally diverse pool of (Z)‐2‐butene‐1,4‐diol monoesters in good yields and with excellent regio‐ and stereoselectivity. Various synthetic transformations of the obtained (Z)‐2‐butene‐1,4‐diol monoesters demonstrate how these synthons are of great use to rapidly diversify the portfolio of these formal desymmetrized (Z)‐alkenes. [ABSTRACT FROM AUTHOR]

Dihydroxyacetone phosphate (DHAP)-dependent aldolases catalyze the aldol addition of DHAP to a variety of aldehydes and generate compounds with two stereocenters. This reaction is useful to synthesize chiral acyclic nucleosides, which constitute a well-known class of antiviral drugs currently used. In such compounds, the chirality of the aliphatic chain, which mimics the open pentose residue, is crucial for activity. In this work, three DHAP-dependent aldolases: fructose-1,6-biphosphate aldolase from rabbit muscle, rhanmulose-1-phosphate aldolase from Thermotoga maritima, and fuculose-1-phosphate aldolase from Escherichia coli, were used as biocatalysts. Aldehyde derivatives of thymine and cytosine were used as acceptor substrates, generating new acyclic nucleoside analogues containing two new stereocenters with conversion yields between 70% and 90%. Moreover, structural analyses by molecular docking were carried out to gain insights into the diasteromeric excess observed. [ABSTRACT FROM AUTHOR]

Strigolactones (SLs) are plant apocarotenoids with diverse roles and structures. Canonical SLs, widespread and characterized by structural variations in their tricyclic lactone (ABC-ring), are classified into two types based on C-ring configurations. The steric C-ring configuration emerges during the BC-ring closure, downstream of the biosyn-thetic intermediate, carlactonoic acid (CLA). Most plants produce either type of canonical SLs stereoselectively, e.g., tomato (Solanum lycopersicum) yields orobanchol with an α-oriented C-ring. The mechanisms driving SL structural diversification are partially understood, with limited insight into functional implications. Furthermore, the exact molecular mechanism for the stereoselective BC-ring closure reaction is yet to be known. We identified an enzyme, the stereoselective BC-ring-forming factor (SRF), from the dirigent protein (DIR) family, specifically the DIR-f subfamily, whose biochemical function had not been characterized, making it a key enzyme in stereoselective canonical SL biosynthesis with the α-oriented C-ring. We first confirm the precise catalytic function of the tomato cytochrome P450 SlCYP722C, previously shown to be involved in orobanchol biosynthesis [T. Wakabayashi et al., Sci. Adv. 5, eaax9067 (2019)], to convert CLA to 18-oxocarlactonoic acid. We then show that SRF catalyzes the stereoselective BC-ring closure reaction of 18-oxocarlactonoic acid, forming orobanchol. Our methodology combines experimental and computational techniques, including SRF structure prediction and conducting molecular dynamics simulations, suggesting a catalytic mechanism based on the conrotatory 4π-electrocyclic reaction for the stereoselective BC-ring formation in orobanchol. This study sheds light on the molecular basis of how plants produce SLs with specific stereochemistry in a controlled manner. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of ¿-aryl carbonyl compounds using palladium catalysis. The authors focus on the deprotonative ¿-arylation of Meyers's chiral bicyclic lactams (MCBLs) as a potential method for synthesizing these compounds. They explore different bases and catalytic systems to optimize the reaction conditions and achieve high yields. The authors also investigate the reaction scope by testing various aryl and heteroaryl bromides. They propose a mechanism for the formation of the arylated lactam products based on their experimental findings. Overall, this study provides valuable insights into the synthesis of ¿-aryl carbonyl compounds and highlights the potential of MCBLs as versatile substrates. [Extracted from the article]

Comprehensive Summary: A general and convenient photoredox‐catalyzed acylation and alkylcyanation of MBH acetates has been established, enabling the assembly of the C(sp2)–C(sp3) bond by a nitrogen‐centered radical strategy for the synthesis of trisubstituted alkenes in moderate to excellent chemical yields (48 examples in total). The reaction of MBH acetates with acyl (indanone) oxime esters afforded trisubstituted alkenes containing 1,4‐dicarbonyl groups. Interestingly, the use of Eosin Y as a photocatalyst in the catalytic system resulted in the formation of distal cyano group‐anchored trisubstituted alkenes via deconstructive functionalization of cycloketone oxime esters. Notably, these resulting 1,4‐dicarbonyl compounds could be applied to late‐stage transformations, providing important methods for the synthesis of dihydropyridazin‐3(2H)‐one. [ABSTRACT FROM AUTHOR]

A new series of chiral 4,5-dihydro-1H-[1,2,4]-triazoline molecules, featuring a β-ᴅ-glucopyranoside appendage, were synthesized via a 1,3-dipolar cycloaddition reaction between various hydrazonyl chlorides and carbohydrate Schiff bases. The isolated enantiopure triazolines (8a–j) were identified through high-resolution mass spectrometry (HRMS) and vibrational spectroscopy. Subsequently, their solution structures were elucidated through NMR spectroscopic techniques. Single-crystal X-ray analysis of derivative 8b provided definitive evidence for the 3-D structure of this compound and revealed important intermolecular forces in the crystal lattice. Moreover, it confirmed the (S)-configuration at the newly generated stereo-center. Selected target compounds were investigated for anti-tumor activity in 60 cancer cell lines, with derivative 8c showing the highest potency, particularly against leukemia. Additionally, substituent-dependent anti-fungal and anti-bacterial behavior was observed. [ABSTRACT FROM AUTHOR]

Adenine diphosphate (ADP)‐ribosylation catalyzed by bacterial toxins is the addition of an ADP‐ribose moiety to specific amino acid residues in target proteins such as arginine, asparagine, glutamine, and histidine through 1,2‐cis(α)‐glycosidic bond formation. ADP‐ribosylation modifies host cell functions, altering normal cellular processes to facilitate their survival, and replication. Despite the development of click chemistry and solid‐phase peptide synthesis‐based approaches, the synthesis of structurally well‐defined naturally occurring N‐linked ADP‐ribosyl molecules remains challenging. Herein, we report a direct and α‐selective N‐ADP‐ribosylation using unprotected β‐ADP‐ribosyl azide and triphenylphosphine esters through traceless Staudinger ligation. The stereoselectivity of this protecting‐group‐free N‐ADP‐ribosylation was validated by enzymatic degradation experiment and high‐performance liquid chromatography, referencing synthetic standards. This method facilitated the facile and rapid synthesis of N‐ADP‐ribosyl acetamide, biotin, fluorescent dye, amino acids, and tripeptide with complete α‐selectivity and moderate yields (37–55 %). [ABSTRACT FROM AUTHOR]

Early/late heterobimetallic complexes are widely recognized as one of the most effective catalysts for activating coupling reactions. Herein, DFT calculations were used to investigate the specific mechanisms of terminal alkyne dimerization facilitated by two types of Zr/Co complexes: the bis (phosphinoamide) complex B and the mono (phosphinoamide) complex C. In addition, their reaction activities were compared with that of three ligand‐bridged Zr/Co complex A. The results show that the activated mechanisms of the three reactions are similar, all of them contain inner‐ and outer‐sphere mechanisms, and the inner one is the optimal process. Compared to A, the terminal alkyne dimerizations activated by B and C have the lower energy barriers and better selectivity for the E‐isomer; thus, the mono‐ and bis‐(phosphinoamide) Zr/Co complexes are expected to show better activity and selectivity than tris (phosphinoamide) complexes. The stereoselectivity of E‐, Z‐, and gem‐isomers is controlled by the reductive elimination process. The IRI analysis reveals that the selectivity for E‐ and Z‐isomers is influenced due to the notable repulsion and vdW interaction between the second alkyne and the MeNPMe2 ligand. Our work provides a theoretical basis for experimental applications and offers inspiration for the design of high selectivity heterobimetallic complexes. [ABSTRACT FROM AUTHOR]

Configurationally‐defined dienes are pervasive across the bioactive natural product spectrum, where they typically manifest themselves as sorbic acid‐based fragments. These C5 motifs reflect the biosynthesis algorithms that facilitate their construction. To complement established biosynthetic paradigms, a chemical platform to facilitate the construction of stereochemically defined, functionalizable dienes by light‐enabled isomerization has been devised. Enabled by selective energy transfer catalysis, a variety of substituted β‐boryl sorbic acid derivatives can be isomerized in a regio‐ and stereo‐selective manner (up to 97 : 3). Directionality is guided by a stabilizing nO→pB interaction in the product: this constitutes a formal anti‐hydroboration of the starting alkyne. This operationally simple reaction employs low catalyst loadings (1 mol %) and is complete in 1 h. X‐ray analysis supports the hypothesis that the nO→pB interaction leads to chromophore bifurcation: this provides a structural foundation for selective energy transfer. [ABSTRACT FROM AUTHOR]

Metal‐hydride‐catalyzed migratory functionalization of alkenes witnessed extensive development in the past few years. However, the asymmetric version of this reaction has remained largely underdeveloped owing to the difficulty in simultaneous control of both regio‐ and stereoselectivity. In addition, exploring the wider alkene substrate scope to enable more synthetically valuable applications represents another challenge in this field. In this context, a nickel‐catalyzed asymmetric hydrocyanation of internal alkenes involving a chain‐walking process is demonstrated. The reaction exhibits excellent regio‐ and enantioselectivity, proceeds under mild reaction conditions, and delivers benzylic nitriles in high yields. Even α,ω‐diaryl internal alkenes, which are known to be one of the most challenging substrates of this type, could be successfully converted to the desired products with good regio‐ and stereoselectivity by modifying the electronic and steric effects. Theoretical calculations suggest that the η3‐benzyl coordination mode and the aryl substituent (3,5‐(OMe)2C6H3) on the diphosphite ligand are both key factors in regulating regio‐ and enantioselectivity. [ABSTRACT FROM AUTHOR]

Because internal alkenes are more challenging synthetic targets than terminal alkenes, metal‐catalyzed olefin mono‐transposition (i.e. positional isomerization) approaches have emerged to afford valuable E‐ or Z‐ internal alkenes from their complementary terminal alkene feedstocks. However, the applicability of these methods has been hampered by lack of generality, commercial availability of precatalysts, and scalability. Here, we report a nickel‐catalyzed platform for the stereodivergent E/Z‐selective synthesis of internal alkenes at room temperature. Commercial reagents enable this one‐carbon transposition of terminal alkenes to valuable E‐ or Z‐internal alkenes via a Ni−H‐mediated insertion/elimination mechanism. Though the mechanistic regime is the same in both systems, the underlying pathways that lead to each of the active catalysts are distinct, with the Z‐selective catalyst forming from comproportionation of an oxidative addition complex followed by oxidative addition with substrate and the E‐selective catalyst forming from protonation of the metal by the trialkylphosphonium salt additive. In each case, ligand sterics and denticity control stereochemistry and prevent over‐isomerization. [ABSTRACT FROM AUTHOR]

Drug combinations and repurposing have recently provided promising alternatives to cope with the increasingly severe issue of antibiotic resistance and depletion of natural drug molecular repertoires that undermine traditional antibacterial strategies. Closantel, an effective adjuvant, reverses antibiotic resistance in gram-negative bacteria. Herein, the combined antibacterial enantioselectivity of closantel is presented through separate enantiomer studies. Despite yielding unexpected differences, two closantel enantiomers (R, S) increased colistin activity against gram-negative bacteria both in vitro and in vivo. The fractional inhibitory concentration indices of R-closantel and Sclosantel combined with colistin against Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli ranged from 0.0087 to 0.5004 and from 0.0117 to 0.5312, respectively. This difference was further demonstrated using growth inhibition assays and time-killing curves. Mechanistically, a higher intracellular concentration of R-CLO is more effective in enhancing the antimicrobial activity of combination. A mouse cutaneous infection model confirmed the synergistic stereoselectivity of closantel. This discovery provides novel insights for developing precision medication and containment of increasing antibiotic resistance. [ABSTRACT FROM AUTHOR]

The proline-catalyzed asymmetric aldol reaction stands as a classic experiment illustrating the concept of enantiomerism. However, due to substrate reactivity limitations and experimental constraints, the stereochemical concepts of diastereoisomerism and racemization have not been adequately addressed. To bridge this gap between experimental and theoretical teaching and enhance students' understanding of stereochemistry in Organic Chemistry, we have innovated and expanded the proline-catalyzed asymmetric aldol reaction. Firstly, by upgrading the conventional two-component reaction to a three-component reaction, we efficiently generate diastereomers through the conversion of arylaldehydes to highly reactive aldimines. Secondly, we introduce the stereoselective control of proline through the use of catalysts with opposite chiral configurations, while also incorporating the concept of racemization by mixing products with opposite configurations. Thirdly, we employ nuclear magnetic resonance (NMR) technology to elucidate the diastereoisomerism ratio of the products, facilitating a deeper understanding of diastereoisomerism concepts. Our results demonstrate that this experiment offers excellent repeatability, appropriate duration, and a balance of exploration and innovation. Implementation of this project not only enhances students' scientific inquiry and innovative thinking but also cultivates their ability to conduct innovative experiments. [ABSTRACT FROM AUTHOR]

Developing simple and benign protocols for synthesizing alkenylboronates is crucial as they are synthetically valuable compounds in various organic transformations. In this work, we report a straightforward ligand‐free protocol for synthesizing alkenylboronates via atom‐economical hydroboration of alkynes with HBpin catalyzed by a manganese salt. The reaction shows a high level of chemo and regioselectivity for the terminal alkynes and exclusively produces E‐selective alkenylboronates. The hydroboration scope is vast, with the resilience of a range of synthetically beneficial functionalities, such as halides, ether, alkenyl, silyl and thiophenyl groups. This reaction proceeds through the involvement of a metal‐hydride intermediate. The developed alkenylboronate can be smoothly converted to useful C‐C, C‐N and C‐I bond‐forming reactions. [ABSTRACT FROM AUTHOR]

The present study describes a multicomponent synthesis of pyridinium derivatives of piperidin-2-ones from aromatic aldehydes, malononitriles, pyridines, haloacetates, and ammonium acetate. The synthesis occurs through the in situ formation of pyridinium ylide and involves the Knoevenagel—Michael—Mannich cyclization cascade. 1-[(3RS,4SR,6RS)-4,6-Diaryl-5,5-dicyano-2-oxopiperidin-3-yl]pyridin-1-ium halides with three stereocenters and 1-[(3RS,4SR,5SR,6RS)-5-alkoxycarbonyl-4,6-diaryl-5-cyano-2-oxopiperidin-3-yl]pyridin-1-ium halides with four stereocenters were synthesized. [ABSTRACT FROM AUTHOR]

The highly stereoselective gem‐silylboration of chiral 2‐substituted 1‐ethynylepoxides is reported herein. The reaction involves first the deprotonation of the epoxides in the acetylenic position followed by transmetallation with Et3SiBpin. The transient silylborane ate‐complexes generated undergo the stereoselective 1,2‐migration of the Et3Si‐group to the sp‐hybridized terminus carbon of the ethynyl‐moiety in a stereospecific anti‐addition. The moisture‐sensitive and thermally unstable 4‐hydroxy‐1‐triethylsilyl‐1‐allenyl(pinacolato)boranes thus obtained react with aldehydes through an SE2'‐mode of addition, affording highly functionalized 2‐triethysilylethynyl‐1,3‐diols with a good diastereoselectivity which is rationalized by a Yamamoto‐Houk type transition state model. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Herein, we report nickel‐catalyzed cross‐coupling of gem‐difluorinated cyclopropanes with boronic acids, providing the corresponding arylated 2‐fluoroallylic scaffolds. This approach used commercially available phosphine ligand Xantphos to obtain monofluorinated alkenes with high regioselectivity and Z‐stereoselectivity. Mechanistic studies proposed a Ni(II)‐fluoroallyl pathway and excluded the radical pathway. Meanwhile, DFT study of the reductive elimination clarified the origin of the high linear selectivity. [ABSTRACT FROM AUTHOR]

Recently, C‐glycosidic bonds have emerged as pivotal elementary units present in many naturally occurring alkaloids as well as in pharmaceutically active molecules. Because of the stability and great utility of C‐glycosides, synthetic approaches en route to the C−C bond formation have gradually become a center of attraction in carbohydrate chemistry. Towards these researches, C‐glycosylation with heteroaryl moieties like indole, and tryptophan can remarkably expand the functional and structural evolution, which has great value for medicinal chemists and chemical biologists. The indolyl and tryptophan‐C‐glycosides have unique structures and biological activities that have attracted a number of synthetic studies. Therefore, these motifs have possessed an extensive interest in the direction of efficient synthesis. Herein, this review systematically summarizes the classical approaches to C‐heteroaryl glycosides mainly focusing on indole and tryptophan synthesis. Furthermore, highlighted the recently developed metal‐catalyzed C−H functionalization and photoinduced cross‐coupling strategies that aim to control the regioselectivity and diastereoselectivity of the reaction in carbohydrate chemistry. In view of reaction type, mechanism, and status, this review will cover the synthesis of indole and tryptophan C‐heteroaryl glycosides with diverse regio‐ and diastereoselectivity from four perspectives which include a) conventional approach, b) heterocyclization and C‐glycosylation sequence, c) metal‐catalyzed C−H functionalization, and d) photoinduced cross‐coupling. 1. Introduction 2. Strategies for the synthesis of indolyl and tryptophan‐C‐glycosides 2.1. Conventional approach 2.2. Heterocyclization and C‐glycosylation sequence 2.3. Metal‐catalyzed C−H functionalization 2.4. Photoinduced cross‐coupling 3. Summary and Outlook [ABSTRACT FROM AUTHOR]

To facilitate the discovery and development of new pharmaceuticals, the demand for novel stereofunctionalised building blocks has never been greater. Whilst molecules bearing quaternary and tetrasubstituted stereogenic centres are ideally suited to explore untapped areas of chemical space, the asymmetric construction ofsterically congested carbon centres remains a longstanding challenge in organic synthesis. The enantioselective assembly of acyclic stereogenic centres is even more demanding due to the need to restrict a much wider range of geometries and conformations of the intermediates involved. In this context, the catalytic asymmetric allylicalkylation (AAA) of acyclic prochiral nucleophiles, namely enolates, has become an indispensable tool to access a range of linearα‐quaternary andα‐tetrasubstituted carbonyl compounds. However, unlike the AAA of cyclic enolates with a fixed enolate geometry, to achieve high levels of stereocontrol in the AAA of acyclic enolates, the stereoselectivity of enolisation must be considered. The aim of this review is to offer acomprehensivediscussion of catalytic AAA reactions of acyclic prochiral enolates and their analogues to generate congested quaternary and tetrasubstituted chiral centres using metal, non‐metal and dual catalysis, with particular focus given to the control of enolate geometry and its impact on the stereochemical outcome of the reaction. [ABSTRACT FROM AUTHOR]

A novel helical poly(phenylisocyanide)-supported catalyst bearing (1R,2R)-1,2-cyclohexanediamine pendant (poly-2m) was synthesized. The chiral cyclohexanediamine polymer catalyst exhibited superior catalytic activity and stereoselectivity in the Michael addition reaction. The polymer poly-2200 catalyzed the Michael addition reaction of cyclohexanone with trans-nitrosostyrene in methanol at the presence of benzoic acid with an enantiomeric excess (ee) value up to 97% and diastereoselectivity (dr) value of 79/21. In addition, the chiral polymer catalyst can be recycled for 3 times in the asymmetric Michael addition reaction without significantly lossing the catalytic activity of the catalyst. Moreover, the chiral cyclohexanediamine catalyst poly-2200 can also catalyze the Aldol reaction of p-nitrobenzaldehyde with cyclohexanone, with ee value of 49% and dr value of 60/40. Asymmetric Michael addition reaction and Aldol reaction catalyzed by poly-2m [ABSTRACT FROM AUTHOR]

This article discusses the development of sustainable catalytic chemical methods for O-glycosylation using iron-based salts as catalysts. The authors experiment with different reaction conditions and optimize the yield of the glycosylation reaction. The study demonstrates the potential of iron-based salts as a sustainable and affordable alternative for large-scale synthesis. The article provides detailed information about the synthesis and characterization of various compounds, including their yields, physical properties, and spectroscopic data. This information can be useful for researchers studying organic chemistry or interested in the synthesis and characterization of specific compounds. [Extracted from the article]

A convergent synthesis of the dodecasaccharide scaffold of axinelloside A was achieved through Au(I)‐catalyzed [6+6] glycosylation. The initially devised [3+1+2] assembly of the nonreducing hexasaccharide fragment was low‐yielding, whereas a convergent [3+3] glycosylation under Au(I) catalysis was proven feasible, allowing for a semi‐gram scale preparation of the wanted hexasaccharide. The requisite 1,2‐cis glycosidic bonds were forged in a highly stereoselective fashion by virtue of remote acetyl group participation, and judicious manipulation of protecting groups. The synthetic dodecasaccharide has been properly protected for the downstream elaboration toward its natural form. [ABSTRACT FROM AUTHOR]