Optimization of enantioselective high-performance liquid chromatography-tandem mass spectrometry method for the quantitative determination of 3,4-methylenedioxy-methamphetamine (MDMA) and its phase-1 metabolites in human biological fluids

Recently we published in this journal an enantioselective high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative determination of 3,4-methylenedioxymethamphetamine (MDMA) and its major phase-1 metabolites, 4-hydroxy-3-methoxyamphetamine (HMA), 4-hydroxy-3-methoxymethamphetamine (HMMA) and 3,4-methylenedioxyamphetamine (MDA) in human plasma, sweat, oral fluid and urine. Since we did not achieve simultaneous enantioseparation of all 4 compounds with a single chiral column, two amylose-based chiral columns were used alternatively. Further optimization of the mobile phase in the present study enabled baseline separation of all four pairs of enantiomers on a single Lux AMP column. In addition, by optimization of the column dimension and applied flow-rate it became possible to complete the separation within 6 minutes. These new methods were applied to the analysis of human plasma, oral fluid and urine. While results on the concentration of MDMA and its metabolites in various biological fluids were reported in our recent publication, in the present study an attempt was made to hydrolyze glucuronides in urine samples by using alternatively, hydrochloric acid or glucuronidase and to evaluate the effect of hydrolysis on the concentration and enantiomeric distribution of hydroxy metabolites of MDMA such as HMA and HMMA.

Stereoisomeric separation of the chiral herbicide profoxydim and residue method development in rice by QuEChERS and LC-MS/MS

A method for the simultaneous determination of the four stereoisomers of the chiral herbicide profoxydim in rice and husk was developed using the QuEChERS method and LC-tandem mass spectrometry. Four polysaccharide-based chiral stationary phase columns were evaluated. All four stereoisomers were successfully separated on a Chiracel OJ-3R column. The effects of mobile phase, modifiers, mobile phase flow rate and temperature on the separation were also investigated. Different QuEChERS methods were compared for the development of an optimized sample preparation procedure. The method, following SANTE guidelines, showed excellent linearity (R2 ≥ 0.99), the LODs were below 4.0 µg kg-1, and the LOQs did not exceed 12.5 µg kg-1. The overall average recoveries at three levels (12.5, 25.0 and 250 µg kg-1) ranged from 76.77 % to 106.53 %, with RSD values less than 7 %. The method is demonstrated to be convenient and reliable for the routine monitoring of profoxydim stereoisomers in rice and husk.

What happens when left meets right under equimolar and non-equimolar co-assembly of short peptide stereoisomers?

The co-assembly of different peptide chains usually leads to the formation of intricate architectures and sophisticated functions in biological systems. Although the co-assembly of stereoisomeric peptides represents a facile and flexible strategy for the synthesis of peptide-based nanomaterials with novel structures and potentially interesting properties, there is a lack of a general knowledge on how different isomers pack during assembly. Through the combined use of simulations and experimental observations, we report that heterochiral pairing is preferred to homochiral pairing at the molecular scale but self-sorting dictates beyond the molecular level for the mixtures of the short stereoisomeric β-sheet peptides I3K (Ile-Ile-Ile-Lys). Furthermore, we demonstrate that flat β-sheets and fibril morphology are always preferred to twisted ones during heterochiral pairing and subsequent assembly. However, the heterochiral pairing into flat morphology is not always at an equimolar ratio. Instead, a non-equimolar ratio (1:2) is observed for the mixing of homochiral LI3LK and heterochiral LI3DK, whose strand twisting degrees differ greatly. Such a study provides a paradigm for understanding the co-assembly of stereoisomeric peptides at the molecular scale and harnessing their blending for targeted nanostructures.

Bifunctional iminophosphorane organocatalyst with additional hydrogen bonding: Calculations predict enhanced catalytic performance in a michael addition reaction

A new iminophosphorane-thiourea superbase was rationally designed and investigated as an organocatalyst for the enantioselective Michael addition reaction of nitromethane to 4-phenylbut-3-en-2-one. Starting from an iminophosphorane-thiourea organocatalyst structure already known, we have used theoretical calculations to determine the structures of transition states involved in the carbon-carbon bond formation step and carried out structural modifications to accelerate the reaction rate and to increase the enantioselectivity. The effective structural modification was adding a rigid hydroxyl group able to make an additional hydrogen bond to the transition state, producing a substantial decrease of the ΔG‡ by 7 kcal mol-1. The enantiomeric excess is predicted to be above of 97% using the reliable M06-2X and ωB97M - V functionals. The determination of the complete reaction mechanism and free energy profile was followed by a detailed microkinetic analysis. The present study points out a new direction for structural modifications on this kind of organocatalyst.

Systemic evaluation of novel acaricide hexythiazox for bioactivity improvement and risk reduction at the enantiomer level

Traditional risk assessments of chiral pesticides mainly depend on racemic form, which is often incomprehensive. This study conducted systemic investigations on the bioactivity, toxicity, and ecotoxicological effects of hexythiazox (HTZ) at the enantiomer level. The elution order and absolute configuration of HTZ enantiomers were determined. (4R, 5R)-(+)-HTZ exhibited 708 and 1719 times higher bioactivity against Tetranychus cinnabarinus and Tetranychus urticae eggs than (4S, 5S)-(-)-HTZ, respectively. Molecular docking indicated greater interactions between (4R, 5R)-(+)-HTZ and chitin synthase leading to higher bioactivity of (4R, 5R)-(+)-HTZ. However, (4S, 5S)-(-)-HTZ induced greater changes in protein and malondialdehyde content, and antioxidant and detoxification enzyme activities than (4R, 5R)-(+)-HTZ in earthworms. Furthermore, integrated biomarker response results indicated (4S, 5S)-(-)-HTZ exhibited higher toxic effects on earthworms than (4R, 5R)-(+)-HTZ. Finally, significant differentially expressed genes (DEGs) were observed in earthworms after exposure to (4R, 5R)-(+)-HTZ and (4S, 5S)-(-)-HTZ, respectively. These DEGs were mainly enriched in glycolysis/gluconeogenesis and purine metabolism pathways in earthworms. Additionally, six metabolism pathways were also enriched, including pyruvate metabolism, fatty acid biosynthesis, oxidative phosphorylation, citric acid cycle, fatty acid degradation, and ATP-binding cassette transporters. These findings suggest that earthworms exhibited enantiomer-specific responses to (4R, 5R)-(+)-HTZ and (4S, 5S)-(-)-HTZ. This study provides systemic insight into the toxicity mechanism of HTZ at the enantiomer level and the potential to develop (4R, 5R)-(+)-HTZ as a high-efficiency and low-risk pesticide.

Chiral carbon dots derived from tryptophan and threonine for enantioselective sensing of L/D-Lysine

Presently, most fluorescent probes for amino acid enantiomers detection require metal ions participation, which greatly increases the detection steps and costs, and affects the accuracy of detection results. To solve this problem, a dual pattern recognition sensor of chiral carbon dots (L-Try-Thr-CDs) with a quantum yield of 36.23 % was prepared by a one-step solvothermal method for the highly selective detection of lysine (Lys) enantiomers. Under optimal experimental conditions, the fluorescence and circular dichroism (CD) signals of the obtained L-Try-Thr-CDs could rapidly and effectively responded to L-Lys with limits of detection (LOD) of 16.51 nM and 24.38 nM, respectively, much lower than previously reported sensors. Importantly, the L-Try-Thr-CDs as a dual-mode sensor could not only detect amino acid enantiomers and simplify the steps, but also avoid inaccurate detection results due to unstable metal ions. Furthermore, the L-Try-Thr-CDs could detect L-Lys in living cells via a fluorescence microscope because of their excellent fluorescence characteristics and low toxicity. These results indicated that the dual-mode sensor not only provided a practical strategy for the design of new fluorescent probes, but also possessed outstanding application prospects in the accurate detection of lysine enantiomers.

A specific chiral HPLC method for lifitegrast and determination of enantiomeric impurity in drug substance, ophthalmic product and stressed samples

Lifitegrast is a lymphocyte function-associated antigen-1 (LFA-1) antagonist used to treat the indications and symptoms associated with dry eye disease (DED), one of the most common ocular surface diseases. Lifitegrast has a chiral center, and the S-enantiomer (S-Lif) is responsible for the therapeutic effects, while the R-enantiomer (R-Lif) lacks efficacy in the treatment of DED. Lifitegrast ophthalmic solution containing 5% lifitegrast was approved by the United States Food and Drug Administration (FDA) in July 2016 for the treatment of DED in patients 17 years of age and older. The objective of this study was to develop a chiral HPLC method for the determination of the enantiomeric impurity of lifitegrast in the drug substance and in the ophthalmic product. In addition, we aimed to investigate the effect of stress and stability conditions on the enantiomeric purity of lifitegrast in both drug substance and ophthalmic solution. During the method development studies, four known lifitegrast impurities (Lif. Imp. A-D) and stressed lifitegrast samples were injected to ensure the specificity of the developed method. The enantiomers of lifitegrast are well separated with a resolution of higher than 4.0. They are also well separated from the peaks of the diluent, impurities, and the placebo used to prepare the ophthalmic solution without interference in 20 min. Chiral separation was achieved using a Chiralpak AD-H column (250 × 4.6 mm, 5.0 μm) at 40 °C with a mobile phase consisting of a mixture of n-hexane, 2-propanol, and formic acid (500:500:2, v/v/v) at a flow rate of 1.0 mL/min and a detection wavelength of 260 nm. Methanol was used as the diluent, and the drug substance solution was found to be stable for 48 h at 15 °C. The optimized chiral HPLC method for lifitegrast was validated according to ICH Q2, and the calibration curves showed excellent linearity for R-Lif (0.0369 - 1.816 µg/mL). This is the first stability-indicating, specific / selective, sensitive, linear, precise, accurate, and robust chiral HPLC method for the determination of R-Lif in S-Lif. The amount of enantiomeric impurity R-Lif in S-Lif increased under all stress and photostability test conditions without exceeding the acceptable impurity limit, with the most significant increase observed at elevated temperatures (105 °C) for both the drug substance in powder form and the ophthalmic drug solution.

Asymmetric Total Synthesis and Structural Revision of DAT2, an Antigenic Glycolipid from Mycobacterium tuberculosis

DAT2 is a member of the diacyl trehalose family (DAT) of antigenic glycolipids located in the mycomembrane of Mycobacterium tuberculosis (Mtb). Recently it was shown that the molecular structure of DAT2 had been incorrectly assigned, but the correct structure remained elusive. Herein, the correct molecular structure of DAT2 and its methyl-branched acyl substituent mycolipanolic acid is determined. For this, four different stereoisomers of mycolipanolic acid were prepared in a stereoselective and unified manner, and incorporated into DAT2. A rigorous comparison of the four isomers to the DAT isolated from Mtb H37Rv by NMR, HPLC, GC, and mass spectrometry allowed a structural revision of mycolipanolic acid and DAT2. Activation of the macrophage inducible Ca2+-dependent lectin receptor (Mincle) with all four stereoisomers shows that the natural stereochemistry of mycolipanolic acid / DAT2 provides the strongest activation, which indicates its high antigenicity and potential application in serodiagnostics and vaccine adjuvants.

Two Sesterterpene Synthases from Lentzea atacamensis Demonstrate the Role of Conformational Variability in Terpene Biosynthesis

Mining of two multiproduct sesterterpene synthases from Lentzea atacamensis resulted in the identification of the synthases for lentzeadiene (LaLDS) and atacamatriene (LaATS). The main product of LaLDS (lentzeadiene) is a new compound, while one of the side products (lentzeatetraene) is the enantiomer of brassitetraene B and the other side product (sestermobaraene F) is known from a surprisingly distantly related sesterterpene synthase. LaATS produces six new compounds, one of which is the enantiomer of the known sesterterpene Bm1. Notably, for both enzymes the products cannot all be explained from one and the same starting conformation of geranylfarnesyl diphosphate, demonstrating the requirement of conformational flexibility of the substrate in the enzymes' active sites. For lentzeadiene an intriguing thermal [1,5]-sigmatropic rearrangement was discovered, reminiscent of the biosynthesis of vitamin D3. All enzyme reactions and the [1,5]-sigmatropic rearrangement were investigated through isotopic labeling experiments and DFT calculations. The results also emphasize the importance of conformational changes during terpene cyclizations.

Collective Synthesis of Highly Oxygenated (Furano)germacranolides Derived from Elephantopus mollis and Elephantopus tomentosus

Germacranolides, secondary metabolites produced by plants, have garnered academic and industrial interest due to their diverse and complex topology as well as a wide array of pharmacological activities. Molephantin, a highly oxygenated germacranolide isolated from medicinal plants, Elephantopus mollis and Elephantopus tomentosus, has exhibited antitumor, inflammatory, and leishmanicidal activities. Its chemical structure is based on a highly strained ten-membered macrocyclic backbone with an (E,Z)-dienone moiety, which is fused with an α-methylene-γ-butyrolactone and adorned with four successive stereogenic centers. Herein, we report the first synthesis of molephantin in 12 steps starting from readily available building blocks. The synthesis features the highly diastereoselective intermolecular Barbier allylation of the β,γ-unsaturated aldehyde with optically active 3-bromomethyl-5H-furan-2-one intermediate and ensuing Nozaki-Hiyama-Kishi (NHK) macrocyclization for the construction of the highly oxygenated ten-membered macrocyclic framework. This synthetic route enabled access to another germacranolide congener, tomenphantopin F. Furthermore, cycloisomerization of molephantin into 2-deethoxy-2β-hydroxyphantomolin could be facilitated by irradiation with ultraviolet A light (λmax=370 nm), which opened a versatile and concise access to the related furanogermacranolides such as EM-2, phantomolin, 2-O-demethyltomenphantopin C, and tomenphantopin C.

RNA-Templated Peptide Bond Formation Promotes L-Homochirality

The world in which we live is homochiral. The ribose units that form the backbone of DNA and RNA are all D-configured and the encoded amino acids that comprise the proteins of all living species feature an all-L-configuration at the α-carbon atoms. The homochirality of α-amino acids is essential for folding of the peptides into well-defined and functional 3D structures and the homochirality of D-ribose is crucial for helix formation and base-pairing. The question of why nature uses only encoded L-α-amino acids is not understood. Herein, we show that an RNA-peptide world, in which peptides grow on RNAs constructed from D-ribose, leads to the self-selection of homo-L-peptides, which provides a possible explanation for the homo-D-ribose and homo-L-amino acid combination seen in nature.

Characterization of two novel hydrolases from Sphingopyxis sp. DBS4 for enantioselective degradation of chiral herbicide diclofop-methyl

Diclofop-methyl, an aryloxyphenoxypropionate (AOPP) herbicide, is a chiral compound with two enantiomers. Microbial detoxification and degradation of various enantiomers is garnering immense research attention. However, enantioselective catabolism of diclofop-methyl has been rarely explored, especially at the molecular level. This study cloned two novel hydrolase genes (dcmA and dcmH) in Sphingopyxis sp. DBS4, and characterized them for diclofop-methyl degradation. DcmA, a member of the amidase superfamily, exhibits 26.1-45.9% identity with functional amidases. Conversely, DcmH corresponded to the DUF3089 domain-containing protein family (a family with unknown function), sharing no significant similarity with other biochemically characterized proteins. DcmA exhibited a broad spectrum of substrates, with preferential hydrolyzation of (R)-(+)-diclofop-methyl, (R)-(+)-quizalofop-ethyl, and (R)-(+)-haloxyfop-methyl. DcmH also preferred (R)-(+)-quizalofop-ethyl and (R)-(+)-haloxyfop-methyl degradation while displaying no apparent enantioselective activity towards diclofop-methyl. Using site-directed mutagenesis and molecular docking, it was determined that Ser175 was the fundamental residue influencing DcmA's activity against the two enantiomers of diclofop-methyl. For the degradation of AOPP herbicides, DcmA is an enantioselective amidase that has never been reported in research. This study provided novel hydrolyzing enzyme resources for the remediation of diclofop-methyl in the environment and deepened the understanding of enantioselective degradation of chiral AOPP herbicides mediated by microbes.

Exploring the neurotoxicity of chiral dinotefuran towards nicotinic acetylcholine receptors: Enantioselective insights into species selectivity

Dinotefuran is a chiral neonicotinoid that is widely distributed in environmental matrices, but its health risks to different organisms are poorly understood. This study investigated the neurotoxic responses of honeybee/cotton aphid nicotinic acetylcholine receptors (nAChRs) to chiral dinotefuran at the enantiomeric scale and demonstrated the microscopic mechanism of species selectivity in nAChR-mediated enantioselective neurotoxicity. The findings indicated that (S)-dinotefuran had a higher affinity for honeybee nAChR than (R)-dinotefuran whereas both enantiomers exhibited similar bioactivity toward cotton aphid nAChR. The results of dynamic neurotoxic processes indicated the association of conformational changes induced by chiral dinotefuran with its macroscopic neurotoxicity, and (R)-dinotefuran, which exhibit low toxicity to honeybee, was found to induce significant conformational changes in the enantioselective neurotoxic reaction, as supported by the average root-mean-square fluctuation (0.35 nm). Energy decomposition results indicated that electrostatic contribution (ΔGele) is the critical energy term that leads to substantial enantioselectivity, and both Trp-51 (－2.57 kcal mol-1) and Arg-75 (－4.86 kcal mol-1), which form a hydrogen-bond network, are crucial residues in mediating the species selectivity for enantioselective neurotoxic responses. Clearly, this study provides experimental evidence for a comprehensive assessment of the health hazards of chiral dinotefuran.

Biotransformation of HBCDs by the microbial communities enriched from mangrove sediments

1,2,5,6,9,10-Hexabromocyclododecanes (HBCDs) are a sort of persistent organic pollutants (POPs). This research investigated 12 microbial communities enriched from sediments of four mangroves in China to transform HBCDs. Six microbial communities gained high transformation rates (27.5-97.7%) after 12 generations of serial transfer. Bacteria were the main contributors to transform HBCDs rather than fungi. Analyses on the bacterial compositions and binning genomes showed that Alcanivorax (55.246-84.942%) harboring haloalkane dehalogenase genes dadAH and dadBH dominated the microbial communities with high transformation rates. Moreover, expressions of dadAH and dadBH in the microbial communities and Alcanivorax isolate could be induced by HBCDs. Further, it was found that purified proteins DadAH and DadBH showed high conversion rates on HBCDs in 36 h (91.9 ± 7.4 and 101.0 ± 1.8%, respectively). The engineered Escherichia coli BL21 strains harbored two genes could convert 5.7 ± 0.4 and 35.1 ± 0.1% HBCDs, respectively, lower than their cell-free crude extracts (61.2 ± 5.2 and 56.5 ± 8.7%, respectively). The diastereoisomer-specific transforming trend by both microbial communities and enzymes were γ- > α- > β-HBCD, differed from α- > β- > γ-HBCD by the Alcanivorax isolate. The identified transformation products indicated that HBCDs were dehalogenated via HBr elimination (dehydrobromination), hydrolytic and reductive debromination pathways in the enriched cultures. Two enzymes converted HBCDs via hydrolytic debromination. The present research provided theoretical bases for the biotransformation of HBCDs by microbial community and the bioremediation of HBCDs contamination in the environment.

Resolution and quantification of carbohydrates by enantioselective comprehensive two-dimensional gas chromatography

Carbohydrates, in particular the d-enantiomers of ribose, 2-deoxyribose, and glucose, are essential to life's informational biopolymers (RNA/DNA) and for supplying energy to living cells through glycolysis. Considered to be potential biosignatures in the search of past or present life, our capacity to detect and quantify these essential sugars is crucial for future space missions to the Moon, Mars or Titan as well as for sample-return missions. However, the enantioselective analysis of carbohydrates is challenging and both research and routine applications, are lacking efficient methods that combine highly sensitive and reproducible detection with baseline enantioselective resolution and reliable enantiomeric excess (ee) measurements. Here, we present four different derivatization strategies in combination with multidimensional gas chromatography coupled to a reflectron time-of-flight mass spectrometer (GC×GC-TOF-MS) for the enantioselective resolution of C3 to C6 carbohydrates potentially suitable for sample-return analyses. Full mass spectral interpretation and calibration curves for one single-step (cyclic boronate derivatives) and three two-step derivatization protocols (aldononitrile-acetate, hemiacetalization-trifluoroacetylation, and hemiacetalization-permethylation) are presented for concentrations ranging from 1 to 50 pmol μL⁻1 with correlation coefficients R2 > 0.94. We compared several analytical parameters including reproducibility, sensitivity (LOD and LOQ), overall separation, chiral resolution (RS), mass spectrum selectivity, stability during long term storage, and reliability of ee measurements to guide the application-dependent selection of optimal separation and quantification performance.

Enantioselective dihydroxylation of xanthorrhizol from Curcuma xanthorrhiza via biotransformation using Aspergillus Niger

Biotransformation is acknowledged as one of the green chemistry methods to synthesis various analogues for further valorization of natural product compounds chemistry and bioactivities. It has huge advantage over chemical synthesis due to its cost-efficiency and higher selectivity. In this work, a xanthorrhizol derivatives, namely (7 R,10S)-10,11-dihydro-10,11-dihydroxyxanthorrhizol was produced in 60% yield from the biotransformation process utilizing A. niger. The structure of the compound was established by extensive spectroscopic methods and comparison with literature data. This biotransformation successfully afforded enantioselective dihydroxylation reaction via green chemistry route. This is the first report on both biotransformation of xanthorrhizol and utilization of A. niger as its biocatalyst.

Origin of Enantioselectivity in Engineered Cytochrome c-Catalyzed Carbon-Radical FePP Hydrolysis Revealed Using QM/MM (ABEEM Polarizable Force Field) and MD Simulations

The origin of highly efficient asymmetric aminohydroxylation of styrene catalyzed by engineered cytochrome c is investigated by the developed Atom-Bond Electronegativity Equalization Method polarizable force field (ABEEM PFF), which is a combined outcome of electronic and steric effects. Model molecules were used to establish the charge parameters of the ABEEM PFF, for which the bond-stretching and angle-bending parameters were obtained by using a combination of modified Seminario and scan methods. The interactions between carbon-radical Fe-porphyrin (FePP) and waters are simulated by molecular dynamics, which shows a clear preference for the pre-R over the pre-S. This preference is attributed to the hydrogen-bond between the mutated 100S and 101P residues as well as van der Waals interactions, enforcing a specific conformation of the carbon-radical FePP complex within the binding pocket. Meanwhile, the hydrogen-bond between water and the nitrogen atom in the active intermediate dictates the stereochemical outcome. Quantum mechanics/molecular mechanics (QM/MM (ABEEM PFF)) and free-energy perturbation calculations elucidate that the 3RTS is characterized by sandwich-like structure among adjacent amino acid residues, which exhibits greater stability than crowed arrangement in 3STS and enables the R enantiomer to form more favorably. Thus, this study provides mechanistic insight into the catalytic reaction of hemoproteins.

Computational insights into the binding modes, keto-enol tautomerization and stereo-electronically controlled decarboxylation of oxaloacetate in the active site of macrophomate synthase

Oxaloacetic acid (OAA) is a β-ketocarboxylic acid, which plays an important role as an intermediate in some metabolic pathways, including the tricarboxylic acid cycle, gluconeogenesis and fatty acid biosynthesis. Animal studies have indicated that supplementing oxaloacetic acid shows an increase of lifespan and other substantial health benefits including mitochondrial DNA protection, and protection of retinal, neural and pancreatic tissues. Most of the chemical transformations of OAA in the metabolic pathways have been extensively studied; however, the understanding of decarboxylation of OAA at the atomic level is relatively lacking. Here, we carried out MD simulations and combined quantum mechanical/molecular mechanical (QM/MM) calculations as an example to systematically elucidate the binding modes, keto-enol tautomerization and decarboxylation of OAA in the active site of macrophomate synthase (MPS), which is a Mg(II)-dependent bifunctional enzyme that catalyzes both the decarboxylation of OAA and [4+2] cycloaddition of 2-pyrone with the decarboxylated intermediate of OAA (pyruvate enolate). On the basis of our calculations, it was found that the Mg2+-coordinated oxaloacetate may exist in enol forms and keto forms. The four keto forms can be transformed into each other by simply rotating the C2-C3 single bond, nevertheless, the keto-enol tautomerization strictly requires the assistance of pocket water molecules. In addition, the decarboxylation is stereo-electronically controlled, i.e., it is the relative orientation of the terminal carboxyl anion that determines the rate of decarboxylation. As such, the chemistry of oxaloacetate in the active site of MPS is complex. On one hand, the most stable binding mode (K-I) may undergo enol-keto tautomerization to isomerize to the enol form, which may further react with the second substrate; on the other hand, K-I may isomerize to another binding mode K-II to proceed decarboxylation to generate pyruvate enolate and CO2. Starting from K-I, the enol-keto tautomerization corresponds to a barrier of 16.2 kcal mol-1, whereas the decarboxylation is associated with an overall barrier of 19.7 kcal mol-1. These findings may provide useful information for understanding the chemistry of OAA and the catalysis of related enzymes, and they are basically in agreement with the available experimental kinetic data.

A Proline-Based Artificial Enzyme That Favors Aldol Condensation Enables Facile Synthesis of Aliphatic Ketones via Tandem Catalysis

A proline-based artificial enzyme is prepared by grafting the l-proline moieties onto the surface of bovine serum albumin (BSA) protein through atom transfer radical polymerization (ATRP). The artificial enzyme, the BSA-PolyProline conjugate, prefers to catalyze the formation of unsaturated ketones rather than β-hydroxy ketones in the reaction between acetone and aldehydes, which is difficult to achieve in free-proline catalysis. The altered reaction selectivity is ascribed to the locally concentrated l-proline moieties surrounding the BSA molecule, indicating a microenvironmental effect-induced switching of the reaction mechanism. Taking advantage of this selectivity, we used this artificial enzyme in conjunction with a natural enzyme, old yellow enzyme 1 (OYE1), to demonstrate a simple synthesis of different aliphatic ketones from acetone and aldehydes via tandem catalysis.

Enantioselective Detection of Gaseous Odorants with Peptide-Graphene Sensors Operating in Humid Environments

Replicating the sense of smell presents an ongoing challenge in the development of biomimetic devices. Olfactory receptors exhibit remarkable discriminatory abilities, including the enantioselective detection of individual odorant molecules. Graphene has emerged as a promising material for biomimetic electronic devices due to its unique electrical properties and exceptional sensitivity. However, the efficient detection of nonpolar odor molecules using transistor-based graphene sensors in a gas phase in environmental conditions remains challenging due to high sensitivity to water vapor. This limitation has impeded the practical development of gas-phase graphene odor sensors capable of selective detection, particularly in humid environments. In this study, we address this challenge by introducing peptide-functionalized graphene sensors that effectively mitigate undesired responses to changes in humidity. Additionally, we demonstrate the significant role of humidity in facilitating the selective detection of odorant molecules by the peptides. These peptides, designed to mimic a fruit fly olfactory receptor, spontaneously assemble into a monomolecular layer on graphene, enabling precise and specific odorant detection. The developed sensors exhibit notable enantioselectivity, achieving a remarkable 35-fold signal contrast between d- and l-limonene. Furthermore, these sensors display distinct responses to various other biogenic volatile organic compounds, demonstrating their versatility as robust tools for odor detection. By acting as both a bioprobe and an electrical signal amplifier, the peptide layer represents a novel and effective strategy to achieve selective odorant detection under normal atmospheric conditions using graphene sensors. This study offers valuable insights into the development of practical odor-sensing technologies with potential applications in diverse fields.

Stereoselective study on chiral fungicide metconazole in four kinds of fruits: Absolute configuration, SFC-MS/MS enantioseparation, degradation and risk assessment

Metconazole is a novel chiral fungicide with two chiral carbon atoms, but the research on its stereoselective behavior is limited. Therefore, the stereoselective behaviors of metconazole in four fruits, including grape, peach, pear and jujube, were summarized in this study. After determining the absolute configuration of metconazole stereoisomers, a chiral separation method through supercritical fluid chromatography/tandem triple quadrupole mass spectrometry was first developed, which combined an improved QuEChERS method obtained the recoveries of 71.6-113 % with RSD ≤ 19.8 %. The LOD and LOQ were 4.30-95.9 and 10.5-143.2 ng/kg, respectively. Different stereoselective and diastereoselective behaviors were observed in four fruits. Dietary risk assessments of rac-metconazole were performed in populations with different ages and genders. Both acute (RQa, 0.0124-0.140 %) and chronic (HQ, 0.0234-0.0794 %) intake risks were acceptable. The results of this study would contribute to more complete risk assessments of metconazole and provide data for chiral studies.

Eat seldom is better than eat frequently: Pharmaceuticals degradation kinetics, enantiomeric profiling and microorganisms in moving bed biofilm reactors are affected by feast famine cycle times

Feast-famine (FF) regimes improved the removal of recalcitrant pharmaceuticals in moving bed biofilm reactors (MBBRs), but the optimal FF cycle remained unresolved. The effects of FF cycle time on the removal of bulk substrates (organic carbon and nitrogen) and trace pharmaceuticals by MBBR are systematically evaluated in this study. The feast to famine ratio was fixed to 1:2 to keep the same loading rate, but the time for the FF cycles varied from 18 h to 288 h. The MBBR adapted to the longest FF cycle time (288 h equaling 48 × HRT) resulted in significantly higher degradation rates (up to +183%) for 12 out of 28 pharmaceuticals than a continuously fed (non-FF) reactor. However, other FF cycle times (18, 36, 72 and 144 h) only showed a significant up-regulation for 2-3 pharmaceuticals compared to the non-FF reactor. Enantioselective degradation of metoprolol and propranolol occurred in the second phase of a two phase degradation, which was different for the longer FF cycle time. N-oxidation and N-demethylation pathways of tramadol and venlafaxine differed across the FF cycle time suggestin the FF cycle time varied the predominant transformation pathways of pharmaceuticals. The abundance of bacteria in the biofilms varied considerably between different FF cycle times, which possibly caused the biofilm to remove more recalcitrant bulk organic C and pharmaceuticals under long cycle times.

Preparation and evaluation of two chiral stationary phases based on imidazolyl-functionalized bromoethoxy pillar[5]arene-bonded silica

Chiral pillar[5]arene-based mesoporous silica, an emerging class of chiral structure, possesses excellent characteristics such as abundant chiral active sites, encapsulated cavity and excellent chiral modification, which make them a promising candidate as new chiral stationary phases (CSPs) in enantioseparation. In this study, two imidazole-containing (S)-1-(4-phenyl-1H-imidazol-2-yl)ethanamine and (S)-Histidinol were respectively modified to bromoethoxy pillar[5]arene-bonded silica to construct new chiral stationary phases (sPIE-BP5-Sil and sHol-BP5-Sil) for the separation and analysis of enantiomers. The separation conditions such as mobile phase composition, flow rate and temperature were optimized. Under optimal conditions, both sPIE-BP5-Sil and sHol-BP5-Sil showed good separation performance for different types of enantiomers. Interestingly, sPIE-BP5-Sil and sHol-BP5-Sil showed better enantioselectivity for chiral aromatic compounds and chiral aliphatic compounds, respectively. This enantioseparation result was closely related to the presence of additional aromatic rings and abundant hydroxyl groups in the side chains of the two chiral groups. In addition, the enantioseparation process was further studied by molecular docking simulation. Therefore, this work provided a new strategy for the preparation and application of imidazolyl-derived pillar[5]arene-based chiral stationary phases, which can be efficiently used for screening and separating enantiomers.

Enantiomeric analysis of γ(δ)-lactones by reversed phase high performance liquid chromatography using amylose tris(5-chloro-2-methylphenylcarbamate) as stationary phase

A Chiralpak AY-3R column was investigated for analytical enantiomeric separation of twelve racemic γ(δ)-lactones using reversed phase high performance liquid chromatography. Main influence factors, including organic modifier, flow rate and column temperature, were optimized. Five kinds of γ(δ)-lactones were successfully enantioseparated using the established method: γ-nonanolactone, δ-decalactone, δ-undecalactone, δ-dodecalactone and δ-tetradecalactone. Under optimized conditions, enantiomeric peak resolution (Rs) for the five γ(δ)-lactones reached more than 1.09, 1.08, 1.54, 1.43, and 1.11, respectively. Their chromatographic elution behavior was investigated using Van't Hoff equation and Van Deemter equation. It was found that an exothermic process occurred during enantiomeric separation of γ(δ)-lactones using this chromatographic column, and it showed a typical Van Deemter curve. Finally, this method was applied in enantiomeric ratio analysis of γ(δ)-lactones contents for purchased butter samples, and results confirmed the predominant content of the (R)-configuration of δ-dodecalactone in natural animal butter, while in margarine, an equal proportion of (R/S)-configuration of δ-dodecalactone was detected.

Supramolecular Hydrogels and Water Channels of Differing Diameters from Dipeptide Isomers

Dipeptides stereoisomers and regioisomers composed of norleucine (Nle) and phenylalanine (Phe) self-assemble into hydrogels under physiological conditions that are suitable for cell culture. The supramolecular behavior, however, differs as the packing modes comprise amphipathic layers or water channels, whose diameter is defined by either four or six dipeptide molecules. A variety of spectroscopy, microscopy, and synchrotron-radiation-based techniques unveil fine details of intermolecular interactions that pinpoint the relationship between the chemical structure and ability to form supramolecular architectures that define soft biomaterials.

Differentiation of solvatomorphs of active pharmaceutical ingredients (API) by solid-state vibrational circular dichroism (VCD)

Here, we present the new application of solid-state Vibrational Circular Dichroism (VCD) spectroscopy to differentiate several dutasteride (DS) solvatomorphs - the model active pharmaceutical ingredient (API). Several crystalline DS hydrochloride hydrates solvated with methanol, ethanol, acetonitrile, acetone, and acetic acid were prepared. In contrast to almost identical IR spectra, the VCD ones were very sensitive to changes in the sample composition. We marked significant differences in the shape of VCD spectra of studied DS solvatomorphs, DS hydrates, and DS polymorphic forms. Our findings, supported by DFT calculations, show that VCD spectroscopy has the pronounced ability to distinguish their crystal arrangements. We believe that this contribution will extend the use of VCD in the pharmaceutical industry for developing and designing new chiral drug products for the identification, description, and in-depth probing of several pharmaceutical solvatomorphs in the future.

Resin-Immobilized Palladium Acetate and Alcohol Dehydrogenase for Chemoenzymatic Enantioselective Synthesis of Chiral Diarylmethanols

The enantioselective synthesis of chiral diarylmethanols is highly desirable in synthetic chemistry and the pharmaceutical industry, but it remains challenging, especially in terms of green and sustainable production. Herein, a resin-immobilized palladium acetate catalyst was fabricated with high activity, stability, and reusability in Suzuki cross-coupling reaction of acyl halides with boronic acids, and the coimmobilization of alcohol dehydrogenase and glucose dehydrogenase on resin supports was also conducted for asymmetric bioreduction of diaryl ketones. Experimental results revealed that the physicochemical properties of the resins and the immobilization modes played important roles in affecting their catalytic performances. These two catalysts enabled the construction of a chemoenzymatic cascade for the enantioselective synthesis of a series of chiral diarylmethanols in high yields (83-90%) and enantioselectivities (87-98% ee). In addition, the asymmetric synthesis of the antihistaminic and anticholinergic drugs (S)-neobenodine and (S)-carbinoxamine was also achieved from the chiral diarylmethanol precursors, demonstrating the synthetic utility of the chemoenzymatic cascade.

Scalable Synthesis of All Stereoisomers of 2-Aminocyclopentanecarboxylic Acid─A Toolbox for Peptide Foldamer Chemistry

Although the construction of peptides with well-defined three-dimensional structures and predictable functions, including biological activity, using conformationally constrained β-amino acids has been shown to be a very successful strategy, their broad application is limited by access to the appropriate building blocks. In particular, trans- and cis-stereoisomers of 2-aminocyclopentanecarboxylic acid (ACPC) are of high interest. The scalable synthesis of all four stereoisomers of Fmoc derivatives of ACPC is presented with NMR-based analysis methods for their enantiomeric purity.

Asymmetric Synthesis of Triazole Antifungal Agents Enabled by an Upgraded Strategy for the Key Epoxide Intermediate

A streamlined and efficient approach to the key epoxide intermediate for the asymmetric synthesis of triazole antifungal agents is presented. This synthesis highlights a P(NMe2)3-mediated nonylidic olefination of α-keto ester, ensuring the exclusive formation of the requisite (Z)-alkene, followed by a highly enantioselective Jacobsen epoxidation to establish the two vicinal stereocenters in a single step. The versatility of this strategy is exemplified through the efficient synthesis of efinaconazole and ravuconazole.

Asymmetric Synthesis of CIDD-0072424 via an Enantioselective Nitro-Mannich Reaction: A Central Nervous System Penetrant, Selective Small Molecule Inhibitor of Protein Kinase C Epsilon

CIDD-0072424 is a novel small molecule developed in silico with remarkable activity for the inhibition of protein kinase C (PKC)-epsilon to treat alcohol use disorder. We developed a concise synthesis of (S)-2 that is highly enantioselective, scalable, and amenable for 3-point structure-activity relationship (SAR) studies for compound optimization. The highly enantioselective nitro-Mannich reaction was achieved through a dual-reagent catalysis system. The overall utility and the efficiency of the enantioselective route provided a scalable synthesis of both PKCε inhibitors 1 and 2.

Design of a gold nanoparticles site in an engineered lipase: an artificial metalloenzyme with enantioselective reductase-like activity

The conjugation of gold complexes with proteins has proved to be interesting and effective in obtaining artificial metalloenzymes as catalysts with improved properties such as higher stability, activity and selectivity. However, the design and precise regulation of their structure as protein nanostructured forms level remains a challenge. Here, we have designed and constructed a gold nanoparticles-enzyme bioconjugate, by tailoring the in situ formation of gold nanoparticles (AuNPs) at two specific sites on the structure of an alkalophilic lipase from Geobacillus thermocatenulatus (GTL). For this purpose, two genetically modified variants of GTL were created by inserting a unique cysteine residue into the catalytic active site by replacing the active serine (GTL-114) and into the lid site (GTL-193). The enzyme, after a first protein-gold coordination, induced the in situ formation of AuNPs, generating a homogeneous artificial enzyme. The size and morphology of the nanoparticles in the AuNPs-enzyme conjugate have been controlled by specific pH conditions in synthesis and the specific protein region where they are formed. Reductase activity of all of them was confirmed in the hydrogenation of nitroarenes in aqueous media. The protein area seemed to be key for the AuNPs, with the best TOF values obtained for the bioconjugates with AuNPs in the lid site. Finally, the protein environment and the asymmetric properties of the AuNPs were tested in the reduction of acetophenone to 1-phenylethanol in aqueous medium at room temperature. A high reductive conversion and an enantiomeric excess of up to 39% towards (R)-1-phenylethanol was found using Au-Mt@GTL-114 pH 10 as a catalyst. Moderate enantioselectivity towards the opposite isomer was also observed using the Au-Mt@GTL-193 pH 10 conjugate.

Enantioselective Divergent Syntheses of Diterpenoid Pyrones

Capitalizing a synergy between late-stage C(sp3)-H alkynylation and a series of transition metal-catalyzed alkyne functionalization reactions, we reported herein enantioselective divergent synthesis of 10 diterpenoid pyrones within 14-16 steps starting from chiral pool enoxolone, including the first enantioselective synthesis of higginsianins A, B, D, E, and metarhizin C. Our synthesis also highlights an unprecedented biomimetic oxidative rearrangement of α-pyrone into 3(2H)-furanone, as well as applications of Echavarren C(sp3)-H alkynylation reaction and Toste chiral counterion-mediated Au-catalyzed intramolecular allene hydroalkoxylation in natural product synthesis.

Synthesis of Chiral Sulfoxides by A Cyclic Oxidation-Reduction Multi-Enzymatic Cascade Biocatalysis

Optically pure sulfoxides are valuable organosulfur compounds extensively employed in medicinal and organic synthesis. In this study, we present a biocatalytic oxidation-reduction cascade system designed for the preparation of enantiopure sulfoxides. The system involves the cooperation of a low-enantioselective chimeric oxidase SMO (styrene monooxygenase) with a high-enantioselective reductase MsrA (methionine sulfoxide reductase A), facilitating "non-selective oxidation and selective reduction" cycles for prochiral sulfide oxidation. The regeneration of requisite cofactors for MsrA and SMO was achieved via a cascade catalysis process involving three auxiliary enzymes, sustained by cost-effective D-glucose. Under the optimal reaction conditions, a series of heteroaryl alkyl, aryl alkyl and dialkyl sulfoxides in R configuration were synthesized through this "one-pot, one step" cascade reaction. The obtained compounds exhibited high yields of >90 % and demonstrated enantiomeric excess (ee) values exceeding 90 %. This study represents an unconventional and efficient biocatalytic way in utilizing the low-enantioselective oxidase for the synthesis of enantiopure sulfoxides.

Enantioselective recognition, synthesis, and separation of pharmaceutical compounds at chiral metallic surfaces

The development of new pharmaceutical compounds is challenging because most of them are based on enantiopure chiral molecules, which exhibit unique properties for therapy. However, the synthesis of pharmaceutical compounds in the absence of a chiral environment naturally leads to a racemic mixture. Thus, to control their synthesis, an asymmetric environment is required, and chiral homogeneous catalysts are typically used to synthesize enantiopure pharmaceutical compounds (EPC). Nevertheless, homogeneous catalysts are difficult to recover after the reaction, generating additional problems and costs in practical processes. Thus, the development of chiral heterogeneous catalysts is a timely topic. In a more general context, such chiral materials cannot only be used for synthesis, but also to recognize and separate enantiomers. In the frame of these different challenges, we give in this review a short introduction to strategies to extrinsically and intrinsically modify heterogeneous metal matrixes for the enantioselective synthesis, recognition, and separation of chiral pharmaceutical compounds.

[Deep eutectic solvents synergistic with carboxymethyl -β-cyclodextrin on the improvement of chiral separation of metoprolol by capillary electrophoresis]

The physical and chemical properties of chiral drugs are very similar. However, their pharmacological and toxicological effects vary significantly. For example, one enantiomer may have favorable properties whereas the other may be ineffective or even have toxic side effects. Hence, exploring innovative strategies to improve enantiomeric resolution is of great importance. Metoprolol (MET) is a β-receptor blocker used to treat hypertension, stable angina pectoris, and supraventricular tachyarrhythmia. Establishing chiral separation and analysis methods of MET enantiomers is important for enhancing the quality of chiral drugs. Capillary electrophoresis (CE) has the advantages of a small sample size, simple operation, high separation efficiency, and many alternative modes; therefore it is widely used in the field of chiral drug separation. The chiral selectors commonly used for CE-based chiral separation include cyclodextrin (CD) and its derivatives, polysaccharides, proteins, and macrocyclic antibiotics. CD is one of the most commonly used and effective chiral selectors for CE. The relatively hydrophobic structure inside the cavity and the relatively hydrophilic structure outside the cavity of CD enable it and chiral molecules to form inclusion compounds with different binding constants, thus achieving chiral separation. However, the use of CD alone as a chiral selector does not always yield satisfactory separation results. Hence, the addition of other additives, such as ionic liquids and deep eutectic solvents (DESs) to assist CD-based chiral separation systems has received extensive attention. Previous studies on the enantiomeric separation of MET by CE have focused on the addition of CD and its derivatives alone for separation. Few studies have been conducted on the synergistic addition of auxiliary additives to CD to improve the enantiomeric resolution of MET. In this study, three DESs, namely, choline chloride-D-glucose, choline chloride-D-fructose, and lactate-D-glucose, were used for the CE-based chiral separation of MET for the first time, and the synergistic effect of the DESs on the separation of MET enantiomers by CD-based capillary zone electrophoresis was speculated. For this purpose, an uncoated fused silica capillary with inner diameter of 50 μm, total length of 50 cm and effective length of 41.5 cm was used as the separation column. First, the effects of CD type, CD concentration, buffer pH, and buffer concentration on MET separation were investigated, and the optimal conditions (15 mmol/L carboxymethyl-β-cyclodextrin (CM-β-CD), pH=3.0, and 40 mmol/L phosphate buffer) were obtained. Other CE conditions were as follows: UV detection at 230 nm, applied voltage of 25 kV. All operations were carried out at 20 ℃. Next, three types of DESs were prepared as auxiliary additives via a mixed-heating method. The DESs were mixed in a 50 mL round-bottomed flask at a certain molar ratio and then heated in a water bath at 80 ℃ for 3 h until a clear and transparent liquid was obtained. The effects of different DESs and their mass fraction on chiral separation were subsequently studied. The optimal choline chloride-D-fructose mass fraction was ultimately determined to be 1.5%. The resolution of MET increased from 1.30 without DES to 2.61 with 1.5% choline chloride-D-fructose, thereby achieving baseline separation. Finally, the separation effect and mechanism were speculated. The MET chiral separation method established in this study is of great significance for improving the quality of chiral compounds and ensuring the safety and effectiveness of clinical drugs. Furthermore, it may be useful in the research and development of CE-based chiral separation techniques using CD derivatives with DESs.

Linear dichroism reveals the perpendicular orientation of DNA bases in the RecA and Rad51 recombinase filaments: A possible mechanism for the strand exchange reaction

Linear dichroism spectroscopy is used to investigate the structure of RecA family recombinase filaments (RecA and Rad51 proteins) with DNA for clarifying the molecular mechanism of DNA strand exchange promoted by these proteins and its activation. The measurements show that the recombinases promote the perpendicular base orientation of single-stranded DNA only in the presence of activators, indicating the importance of base orientation in the reaction. We summarize the results and discuss the role of DNA base orientation.

Preparation of amino acid chiral ionic liquid and visual chiral recognition of glutamine and phenylalanine enantiomers

In this paper, the amino acid chiral ionic liquid (AACIL) was prepared with L-phenylalanine and imidazole. It was characterized by CD, FT-IR, 1H NMR, and 13C NMR spectrum. The chiral recognition sensor was constructed with AACIL and Cu(II), which exhibited different chiral visual responses (solubility or color difference) to the enantiomers of glutamine (Gln) and phenylalanine (Phe). The effects of solvent, pH, time, temperature, metal ions, and other amino acids on visual chiral recognition were optimized. The minimum concentrations of Gln and Phe for visual chiral recognition were 0.20 mg/ml and 0.28 mg/ml, respectively. The mechanism of chiral recognition was investigated by FT-IR, TEM, SEM, TG, XPS, and CD. The location of the host-guest inclusion or molecular placement has been conformationally searched based on Gaussian 09 software.

Deciphering the Absolute Configuration of Murgantiol Isomers in the Pheromone Blend of the Rice Stink Bug, Mormidea v-luteum (Hemiptera, Pentatomidae)

The males-produced pheromone blend of the Mormidea v-luteum (Hemiptera, Pentatomidae) consists in two isomers of zingiberenol (1) and three of murgantiol (2). While the absolute configuration of the zingiberenol isomers has been described, the configurations of the murgantiol isomers remained unexplored. So, our objective was to identify the absolute configuration of the murgantiol isomers (2 a-c) in the pheromone blend. To achieve this, we initially performed dehydration of the natural extract followed by enantiomeric resolution and, as a result, the three isomers was identified as (4R,1'S)-murgantiol. By leveraging the fixed cis and trans relationships among all pheromone components, we established the configuration at C-1 for isomers 2 a and 2 b is S, while that of 2 c is R. Finally, employing microchemical Sharples asymmetric dihydroxylation and epoxide ring closure, we determined the absolute configuration of the epoxide ring. Consequently, the natural isomers 2 a, 2 b, and 2 c were identified as (1S,4R,1'S,4'R)-, (1S,4R,1'S,4'S)-, and (1R,4R,1'S,4'S)-murgantiol, respectively.

Be aware of (R)-methamphetamine: Negative immunoassay versus positive confirmation analysis

The amphetamine-type stimulant methamphetamine exists in two enantiomeric forms, (S)-methamphetamine and (R)-methamphetamine, which are both psychoactive but with the (S)-enantiomer being more potent than the (R)-enantiomer. Illicit methamphetamine encountered in Europe is typically a racemic mixture of both enantiomers and enantiopure (S)-methamphetamine, respectively. However, herein we report two cases with proven enantiopure (R)-methamphetamine consumption with moreover both cases remaining undetected by immunoassay screening. Inconspicuous immunoassay findings can be traced back to a considerably higher sensitivity and concentration-dependent cross-reactivity of the applied drug of abuse assay for the (S)-enantiomer of methamphetamine compared with the (R)-enantiomer, and this limitation should be well known by users of immunoassay drug tests.

Supramolecular Chiral Binding Affinity-Achieved Efficient Synergistic Cancer Therapy

Supramolecular chirality-mediated selective interaction among native assemblies is essential for precise disease diagnosis and treatment. Herein, to fully understand the supramolecular chiral binding affinity-achieved therapeutic efficiency, supramolecular chiral nanoparticles (WP5⊃D/L-Arg+DOX+ICG) with the chirality transfer from chiral arginine (D/L-Arg) to water-soluble pillar[5]arene (WP5) are developed through non-covalent interactions, in which an anticancer drug (DOX, doxorubicin hydrochloride) and a photothermal agent (ICG, indocyanine green) are successfully loaded. Interestingly, the WP5⊃D-Arg nanoparticles show 107 folds stronger binding capability toward phospholipid-composed liposomes compared with WP5⊃L-Arg. The enantioselective interaction further triggers the supramolecular chirality-specific drug accumulation in cancer cells. As a consequence, WP5⊃D-Arg+DOX+ICG exhibits extremely enhanced chemo-photothermal synergistic therapeutic efficacy (tumor inhibition rate of 99.4%) than that of WP5⊃L-Arg+DOX+ICG (tumor inhibition rate of 56.4%) under the same condition. This work reveals the breakthrough that supramolecular chiral assemblies can induce surprisingly large difference in cancer therapy, providing strong support for the significance of supramolecular chirality in bio-application.

Biocatalytic enantioselective synthesis of cenobamate, an antiepileptic drug

A green and efficient process for the synthesis of cenobamate has been accomplished in 70% yield and >99% ee through the bio-reduction of β-ketotetrazole using Daucus carota whole plant cells. The corresponding β-hydroxytetrazole was isolated in 60% yield and >98% ee. This is the first report on the biocatalytic reduction of β-ketotetrazole using plant enzymes derived from D. carota root cells with excellent enantioselectivity.

Arylacetonitrilases: Potential Biocatalysts for Green Chemistry

Nitrilases are the enzymes that catalyze the hydrolysis of nitriles to corresponding carboxylic acid and ammonia. They are broadly categorized into aromatic, aliphatic, and arylacetonitrilases based on their substrate specificity. Most of the studies pertaining to these enzymes in the literature have focused on aromatic and aliphatic nitrilases. However, arylacetonitrilases have attracted the attention of academia and industry in the last several years due to their aryl specificity and enantioselectivity. They have emerged as interesting biocatalytic tools in green chemistry to synthesize useful aryl acids such as mandelic acid and derivatives of phenylacetic acid. The aim of the present review is to collate information on the arylacetonitrilases and their catalytic properties including enantioselectivity and potential applications in organic synthesis.

Stereoselective total synthesis of arachnid harvestmen natural product: (4S,5S)‑4-hydroxy-γ-decalactone

Herein, we described the novel synthetic strategy for the total synthesis of harvestmen natural product (4S,5S)‑4-hydroxy-γ-decalactone (minor) from an inexpensive precursor ((R)-2,2-dimethyl-1,3-dioxolane-4-carbaldehyde) with 31% overall yield. Hydroxy-γ-lactones represent a special class of harvestmen exocrine defense compounds. The present convergent synthesis utilizes classical reactions like the Barbier reaction, the Grignard reaction, and the employment of an olefin as a masked carboxylic acid functionality followed by lactone formation as key steps.

Activation-Induced Senescent Cell Death based on Chiral CoHAu Nanoassemblies with Enantioselective Cascade-Catalytic Ability

Chirality is common in nature, which determines the high enantioselectivity of living systems. Selecting suitable chiral configurations is of great meaning for nanostructures to function better in biological systems. In this study, chiral Co3O4-H2TPPS-Au (CoHAu) nanoassemblies are constructed to accelerate the production ∙OH by consuming D-glucose (D-Glu, widely spread in nature) based on their outstanding enantioselective cascade-catalytic abilities. In particular, D-CoHAu nanoassemblies are more effective in the catalytic conversion of D-Glu than L-CoHAu nanoassemblies. This phenomenon is due to the stronger binding affinity of D-CoHAu nanoassemblies indicated by the lower Km value. Moreover, D-CoHAu nanoassemblies display excellent consumption-ability of D-Glu and production of ∙OH in living cells, which can eliminate senescent cells effectively based on their intracellular enantioselective cascade-catalysis. This research establishes the foundation for bio-mimicking nanostructures with unique functionalities to regulate abnormal biological activities better.

Development of a three-dimensional HPLC system for the determination of serine, threonine and allo-threonine enantiomers in the plasma of patients with chronic kidney disease

A highly-selective three-dimensional high-performance liquid chromatographic (3D-HPLC) system was developed for the determination of serine (Ser), threonine (Thr) and allo-threonine (aThr) enantiomers in human plasma to screen the new biomarker of chronic kidney disease (CKD). d-Ser has been reported to be the candidate biomarker of CKD, however, multiple biomarkers are still required. Therefore, Ser analogs of hydroxy amino acids are the focus in the present study. For the sensitive analysis, the amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole and detected by their fluorescence. The 3D-HPLC system consisted of a reversed-phase column (Singularity RP18, 1.0 × 250 mm), an anion-exchange column (Singularity AX, 1.0 × 150 mm) and a Pirkle-type chiral stationary phase (Singularity CSP-013S, 1.5 × 250 mm). The developed method was validated and applied to the human plasma samples obtained from 15 healthy volunteers and 165 CKD patients. The concentrations of the d-forms were 1.13-2.26 (Ser), 0.01-0.03 (Thr) and 0.04-0.10 μM (aThr) for the healthy volunteers and 0.95-19.0 (Ser), 0-0.57 (Thr) and 0.04-1.02 μM (aThr) for the CKD patients. The concentrations and the %d values of all the target d-amino acids were increased along with the decreasing of renal function and further investigation for clinical applications are expected.

Chiral recognition without π-π-interactions: Highly efficient chiral strong cation exchangers lacking an aromatic unit in the molecular structure

Current state-of-the-art chiral stationary phases (CSPs) enable chiral resolution of almost any racemic mixture of choice. The exceptions represent ionizable and ionized substances that fail at any attempts to resolve on commercially available CSPs. These compounds, however, can be efficiently separated on chiral ion exchangers. Commercially available Cinchona alkaloids-based chiral weak ion-exchangers are typically used for chiral resolution of organic acids, while zwitterion ion-exchangers are efficient in the resolution of acids, bases, and zwitterions. The latter possess in their structure a cation exchange unit, which alone can serve as a cornerstone of chiral strong cation exchangers facilitating chiral separation of various basic racemic mixtures. Although chiral strong cation exchangers (cSCX) are efficient CSPs, their structural variations have not been thoroughly studied so far. It was assumed that the mechanism of chiral recognition of basic compounds by cSCX is based predominantly on π-π-interactions, hydrogen bonding and steric interactions (CSP I). To verify this assumption, we aimed in our study on the design and synthesis of cSCX first lacking lateral polar substituents on the aromatic unit in the selector's structure (CSP II), and second, to replace the aromatic unit by a cyclohexane ring (CSP III and IV), thereby to omit completely the π-π-interactions. We hypothesized that this structural change should lead to a partial or complete loss of enantiorecognition power of the selectors. Surprisingly, the non-aromatic cSCXs have shown chiral recognition capability comparable to that of previously described chiral cation exchange-type CSPs: from 16 analytes screened, 11 analytes were baseline resolved and 5 partially resolved on CSP I, while non-aromatic CSP III resolved 10 analytes baseline and 6 partially. We discuss the structural motifs of the known cSCX and the novel non-aromatic selectors in a relationship with their chromatographic performance using a set of basic analytes. Moreover, we present a theory of an effective chiral recognition mechanism by two novel non-aromatic cSCXs based on the chromatographic results and quantum mechanical calculations.

Enantioselective Sulfonimidamide Acylation via a Cinchona Alkaloid-Catalyzed Desymmetrization: Scope, Data Science, and Mechanistic Investigation

Methods to access chiral sulfur(VI) pharmacophores are of interest in medicinal and synthetic chemistry. We report the desymmetrization of unprotected sulfonimidamides via asymmetric acylation with a cinchona-phosphinate catalyst. The desired products are formed in excellent yield and enantioselectivity with no observed bis-acylation. A data-science-driven approach to substrate scope evaluation was coupled to high throughput experimentation (HTE) to facilitate statistical modeling in order to inform mechanistic studies. Reaction kinetics, catalyst structural studies, and density functional theory (DFT) transition state analysis elucidated the turnover-limiting step to be the collapse of the tetrahedral intermediate and provided key insights into the catalyst-substrate structure-activity relationships responsible for the origin of the enantioselectivity. This study offers a reliable method for accessing enantioenriched sulfonimidamides to propel their application as pharmacophores and serves as an example of the mechanistic insight that can be gleaned from integrating data science and traditional physical organic techniques.

Evaluation of Individual Variation of d-Amino Acids in Human Plasma by a Two-Dimensional LC-MS/MS System and Application to the Early Diagnosis of Chronic Kidney Disease

For the discovery of sensitive biomarkers of kidney function focusing on chiral amino acids, a multiple heart-cutting two-dimensional (2D) liquid chromatography-mass spectrometry (LC-MS)/MS system has been designed/developed. As the target analytes, alanine (Ala), aspartic acid, glutamic acid (Glu), leucine (Leu), lysine, methionine, phenylalanine (Phe), proline (Pro), serine (Ser), and valine were selected considering the presence of their d-forms in mammals. The 2D LC-MS/MS system consisted of the nonenantioselective reversed-phase separation of the target amino acids, the separations of the d- and l-enantiomers, and detection using MS/MS. Using the method, the plasma chiral amino acids, precolumn derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole, were isolated from other intrinsic substances, then determined without losing sensitivity by the fully automated whole-peak volume transfer operation from first to second dimension. In all of the tested plasma samples obtained from five healthy individuals and 15 patients with chronic kidney disease (CKD), the target chiral amino acids were determined without interference. In healthy individuals, the levels of all the tested d-amino acids were regulated in the low ranges. In contrast, the % d values of Glu, Leu, and Phe significantly increased with the progress of kidney dysfunction, besides the previously reported values of d-Ala, Pro, and Ser. Concerning Phe, the significant increase of the % d values (p < 0.05) was reported for the first time even in the mild CKD group compared to those of the healthy group; d-Phe might be a more sensitive marker than the previously reported d-forms. These results demonstrated the potential of these d-forms as the sensitive biomarkers of kidney function for the early diagnosis of CKD.

Physics-Informed Deep Learning Approach for Reintroducing Atomic Detail in Coarse-Grained Configurations of Multiple Poly(lactic acid) Stereoisomers

Multiscale modeling of complex molecular systems, such as macromolecules, encompasses methods that combine information from fine and coarse representations of molecules to capture material properties over a wide range of spatiotemporal scales. Being able to exchange information between different levels of resolution is essential for the effective transfer of this information. The inverse problem of reintroducing atomistic degrees of freedom in coarse-grained (CG) molecular configurations is particularly challenging as, from a mathematical point of view, it is an ill-posed problem; the forward mapping from the atomistic to the CG description is typically defined via a deterministic operator ("one-to-one" problem), whereas the reversed mapping from the CG to the atomistic model refers to creating one representative configuration out of many possible ones ("one-to-many" problem). Most of the backmapping methods proposed so far balance accuracy, efficiency, and general applicability. This is particularly important for macromolecular systems with different types of isomers, i.e., molecules that have the same molecular formula and sequence of bonded atoms (constitution) but differ in the three-dimensional configurations of their atoms in space. Here, we introduce a versatile deep learning approach for backmapping multicomponent CG macromolecules with chiral centers, trained to learn structural correlations between polymer configurations at the atomistic level and their corresponding CG descriptions. This method is intended to be simple and flexible while presenting a generic solution for resolution transformation. In addition, the method is aimed to respect the structural features of the molecule, such as local packing, capturing therefore the physical properties of the material. As an illustrative example, we apply the model on linear poly(lactic acid) (PLA) in melt, which is one of the most popular biodegradable polymers. The framework is tested on a number of model systems starting from homopolymer stereoisomers of PLA to copolymers with randomly placed chiral centers. The results demonstrate the efficiency and efficacy of the new approach.

High anti Diastereoselectivity in a Tandem Oxyhomologation-Coupling Protocol for the Preparation of Amides and Peptides Incorporating α-Hydroxy β-Amino Acids

The one-pot MAC (Masked Acyl Cyanide) reaction is used to perform the tandem oxyhomologation reaction of N,N-dibenzyl-l-phenylalaninal and coupling with nitrogen nucleophiles to provide a wide selection of amide and peptide derivatives of (2S,3S)-allophenylnorstatin in generally good yields and with high anti selectivity, often with dr >98:2. The procedure works equally well with other selected N,N-dibenzyl α-amino aldehydes, and is used to achieve a very short synthesis of (2S,3S,S)-epibestatin.