Zn-Catalyzed Enantioselective Allylation and Allenylation of Isatins by virtue of Proline-derived Chiral Ligand

An asymmetric allylation and allenylation of isatins with facile organoboron reagents was developed under the catalysis of Lewis acid. A series of optically pure 3-allyl-3-hydroxyoxindoles and 3-allenyl-3-hydroxyoxindoles can be obtained...

Chiral FexCuySe nanoparticles as peroxidase mimics for colorimetric detection of 3, 4-dihydroxy-phenylalanine enantiomers

L-3,4-dihydroxy-phenylalanine (L-dopa) is the most widely used drug in Parkinson's disease treatment. However, development of cost-effective and high-throughput sensors to accurate enantioselective discrimination of L-dopa and D-dopa remains challenging to date. Herein, on the basis of the peroxidase-mimic activity of chiral FexCuySe nanoparticles, we demonstrated a novel colorimetric sensor for determination of chiral dopa. The surface chiral ligand, L/D-histidine (L/D-His), endowed the nanozymes with enantioselectivity in catalyzing the oxidation of dopa enantiomers. According to the values of kcat/Km, the efficiency of L-His modified nanoparticle (L-FexCuySe NPs) towards L-dopa was 1.56 times higher than that of D-dopa. While, D-His can facilely reverse the preference of the nanozyme to D-dopa. On the basis of high catalytic activity and enantioselectivity of L-FexCuySe NPs in oxidation of L-dopa, the L-FexCuySe NPs based system can be utilized for detection of L-dopa. The linear ranges for L-dopa determination were 5 µM to 0.125 mM and 0.125 mM to 1 mM with a detection limit of 1.02 µM. Critically, the developed sensor has been successfully applied in the quality control of clinical used L-dopa tablets. Our work sheds light on developing simple and sensitive chiral nanomaterials-based sensors for drug analysis.

Ni-catalyzed hydroalkylation of olefins with N-sulfonyl amines

Hydroalkylation, the direct addition of a C(sp3)–H bond across an olefin, is a desirable strategy to produce valuable, complex structural motifs in functional materials, pharmaceuticals, and natural products. Herein, we report a reliable method for accessing α-branched amines via nickel-catalyzed hydroalkylation reactions. Specifically, by using bis(cyclooctadiene)nickel (Ni(cod)2) together with a phosphine ligand, we achieved a formal C(sp3)–H bond insertion reaction between olefins and N-sulfonyl amines without the need for an external hydride source. The amine not only provides the alkyl motif but also delivers hydride to the olefin by means of a nickel-engaged β–hydride elimination/reductive elimination process. This method provides a platform for constructing chiral α-branched amines by using a P-chiral ligand, demonstrating its potential utility in organic synthesis. Notably, a sulfonamidyl boronate complex formed in situ under basic conditions promotes ring-opening of the azanickellacycle reaction intermediate, leading to a significant improvement of the catalytic efficiency.

Kinetic Resolution by Lithiation: Highly Enantioselective Synthesis of Substituted Dihydrobenzoxazines and Tetrahydroquinoxalines

Kinetic resolution provided a highly enantioselective method to access a range of 3-aryl-3,4-dihydro-2H-1,4-benzoxazines using n-butyllithium and the chiral ligand sparteine. The enantioenrichment remained high on removing the tert-butoxycarbonyl (Boc) protecting group. The intermediate organolithium undergoes ring-opening to an enamine. The kinetic resolution was extended to give enantiomerically enriched substituted 1,2,3,4-tetrahydroquinoxalines and was applied to a synthesis of an analog of the antibiotic levofloxacin that was screened for its activity against the human pathogen Streptococcus pneumoniae.

Palladium/N-CD3-Xu-Phos-catalyzed enantioselective cascade Heck/remote C(sp2)−H alkylation reaction

Heck-type C-H bond activation of unactivated alkenes has emerged as a powerful strategy for the construction of synthetically valuable spirocycles over past 30 years, however, the development of asymmetric version has lagged largely behind. Herein we demonstrate a robust Heck-type reaction of a broad range of unactivated alkenes enabled by the first palladium/Xu-Phos-catalyzed tandem Heck/remote C−H bond alkylation. Moreover, the synthesis of both enantiomers of the product using the same enantiomer of a chiral ligand via a position of the phenyl ring-dependent enantiodivergent synthesis. The salient features of this methodology include operational simplicity, high chemo- and enantioselectivity, broad substrate scope. In addition, we first revealed that the C(sp2)-H activation, alkene insertion and C−I reductive elimination steps are reversible by experiments.

Origin of Enantioselectivity Reversal in Lewis Acid-Catalysed Michael Additions Relying on the Same Chiral Source

Enantiodivergence is an important concept in asymmetric catalysis that enables access to both enantiomers of a product relying on the same chiral source as reagent. This strategy is particularly appealing as an alternate approach when only one enantiomer of the required chiral ligand is readily accessible but both enantiomers of the product are desired. Despite the potential significance, general catalytic methods to effectively reverse enantioselectivity by changing an achiral reaction parameter remain underdeveloped. Herein we report our studies focused on elucidating the origin of metal-controlled enantioselectivity reversal in Lewis acid-catalysed Michael additions. Rigorous experimental and computational investigations reveal that specific interactions between the substrate and ligand depending on the choice of metal catalyst are a key factor responsible for the observed enantiodivergence. This holds potential to further our understanding of and facilitate the design of future enantiodivergent transformations.

Polydopamine-Assisted Rapid One-Step Immobilization of L-Arginine in Capillary as Immobilized Chiral Ligands for Enantioseparation of Dansyl Amino Acids by Chiral Ligand Exchange Capillary Electrochromatography

Herein, a novel L-arginine (L-Arg)-modified polydopamine (PDA)-coated capillary (PDA/L-Arg@capillary) was firstly fabricated via the basic amino-acid-induced PDA co-deposition strategy and employed to constitute a new chiral ligand exchange capillary electrochromatography (CLE-CEC) method for the high-performance enantioseparation of D,L-amino acids (D,L-AAs) with L-Arg as the immobilized chiral ligand coordinating with the central metal ion Zn(II) as running buffer. Assisted by hydrothermal treatment, the robust immobilization of L-Arg on the capillary inner wall could be facilely achieved within 1 h, prominently improving the synthesis efficiency and simplifying the preparation procedure. The successful preparation of PDA/L-Arg coatings in the capillary was systematically characterized and confirmed using several methods. In comparison with bare and PDA-functionalized capillaries, the enantioseparation capability of the presented CLE-CEC system was significantly enhanced. Eight D,L-AAs were completely separated and three pairs were partially separated under the optimal conditions. The prepared PDA/L-Arg@capillary showed good repeatability and stability. The potential mechanism of the greatly enhanced enantioseparation performance obtained by PDA/L-Arg@capillary was also explored. Moreover, the proposed method was further utilized for studying the enzyme kinetics of L-glutamic dehydrogenase, exhibiting its promising prospects in enzyme assays and other related applications.

Absence of Non-Linear Effects Despite Evidence for Catalyst Aggregation

<p>An in-depth study of the catalytic system, consisting of the enantioselective addition of ZnEt₂ to benzaldehyde with (1<i>R</i>,2<i>S</i>)-(-)-N-Methylephedrine (NME) as chiral ligand, suggests the presence of dimeric and trimeric aggregates, as deduced from product ee vs catalyst loading and NMR investigations (¹H, DOSY). Formation of catalyst aggregate was excluded in earlier studies as this system displays a linear product ee vs ligand ee-correlation, which is usually taken as an indication for the <i>absence</i> of catalyst aggregation. A subsequent theoretical study, using the monomer-dimer competition model we recently have developed, highlights the possible parameter configurations leading to linear product ee vs ligand ee plots – despite the presence of catalyst dimers. It shows that, while the Kagan and Noyori models allow linearity in very specific cases only, a multitude of scenarios may lead to linearity here, especially if heterochiral dimers are catalytically active.</p>