Separations and analyses of chiral compounds are important in many fields, including pharmaceutical production, preparation of chemical intermediates, and biochemistry. High‐performance liquid ...chromatography using a chiral stationary phase is regarded as one of the most valuable methods for enantiomeric separation and analysis because it is highly efficient, is broadly applicable, and has powerful separation capability. The focus for development of this method is the identification of novel chiral stationary phases with superior recognition performance and good stability. The present article reviews recent progress in the development of new chiral stationary phases for high‐performance liquid chromatography between January 2018 and June 2021. These newly reported chiral stationary phases are divided into three categories: small organic molecule‐based (cyclodextrin and its derivatives, macrocyclic antibiotics, cinchona alkaloids, and other low molecular weight chiral molecules), macromolecule‐based (cellulose and amylose derivatives, chitin and chitosan derivatives, and synthetic helical polymers) and chiral porous material‐based (chiral metal‐organic frameworks, chiral covalent organic frameworks, and chiral inorganic mesoporous silicas). Each type of chiral stationary phase is discussed in detail.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The separation of enantiomers by chromatographic methods, such as gas chromatography, high‐performance liquid chromatography and capillary electrochromatography, has become an increasingly ...significant challenge over the past few decades due to the demand of pharmaceutical, agrochemical, and food analysis. Among these chromatographic resolution methods, high‐performance liquid chromatography based on chiral stationary phases has become the most popular and effective method used for the analytical and preparative separation of optically active compounds. This review mainly focuses on the recent development trends for novel chiral stationary phases based on chitosan derivatives, cyclofructan derivatives, and chiral porous materials that include metal‐organic frameworks and covalent organic frameworks in high‐performance liquid chromatography. The enantioseparation performance and chiral recognition mechanisms of these newly developed chiral selectors toward enantiomers are discussed in detail.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Porous materials with well‐defined pore structures have received considerable attention in the past decades due to their unique structures and wide applications. Most porous materials such as ...zeolites, metal‐organic frameworks, covalent organic frameworks, and porous organic polymers are extended to infinite frameworks or networks by robust covalent or coordination bonds. Porous molecular cages composed of discrete molecules with permanent cavities are an emerging class of porous material and the discrete molecules assemble into solids by weak intermolecular interaction. In comparison to porous extended solids such as metal‐organic frameworks and covalent organic frameworks, porous molecular cage solids are generally soluble in organic solvents thus allowing solution processing, making them more convenient to apply in many fields. This review mainly focuses on the recent advances of application of porous molecular cages (porous organic cages and metal‐organic cages) for enantioselective recognition and separation from 2010 to present, including gas chromatography, capillary electrochromatography, chiral fluorescent recognition, chiral potentiometric sensing, and enantioselective adsorption. Furthermore, the two important family members of porous molecular cages, porous organic cages and metal‐organic cages, are also discussed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Chromatography techniques based on chiral stationary phases are widely used for the separation of enantiomers. In particular, gas chromatography has developed rapidly in recent years due to its ...merits such as fast analysis speed, lower consumption of stationary phases and analytes, higher column efficiency, making it a better choice for chiral separation in diverse industries. This article summarizes recent progress of novel chiral stationary phases based on cyclofructan derivatives and chiral porous materials including chiral metal–organic frameworks, chiral porous organic frameworks, chiral inorganic mesoporous materials, and chiral porous organic cages in gas chromatography, covering original research papers published since 2010. The chiral recognition properties and mechanisms of separation toward enantiomers are also introduced.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A highly enantioselective dearomative 3+2 cycloaddition of benzothiazole has been successfully developed. A wide range of benzothiazoles and cyclopropane‐1,1‐dicarboxylates are suitable substrates ...for this reaction. The desired hydropyrrolo2,1‐bthiazole compounds were obtained in excellent enantioselectivity and yields (up to 97 % ee and 97 % yield). With the same catalytic system, a highly efficient kinetic resolution of 2‐substituted cyclopropane‐1,1‐dicarboxylates was also realized.
A highly enantioselective dearomative 3+2 cycloaddition of benzothiazole has been successfully developed. A wide range of benzothiazoles and cyclopropane‐1,1‐dicarboxylates are suitable substrates for this reaction. The desired hydropyrrolo2,1‐bthiazole compounds were obtained in excellent enantioselectivity and yields. With the same catalytic system, a highly efficient kinetic resolution of 2‐substituted cyclopropane‐1,1‐dicarboxylates was also realized.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A DMAP‐N‐oxide, featuring an α‐amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O‐acylated azlactones afforded C‐acylated ...azlactones possessing a quaternary stereocenter in high yields (up to 97 % yield) and excellent enantioselectivities (up to 97 % ee). Compared to the widespread use of pyridine nitrogen, which serves as the nucleophilic site in the asymmetric acyl transfer reaction, we discovered that chiral DMAP‐N‐oxides, in which the oxygen now acts as the nucleophilic site, are efficient acyl transfer catalysts. Our finding might open a new door for the development of chiral DMAP‐N‐oxides for asymmetric acyl transfer reactions.
A DMAP‐N‐oxide, featuring an α‐amino acid as the chiral source, was developed, synthesized and applied in asymmetric Steglich rearrangement. A series of O‐acylated azlactones afforded C‐acylated azlactones possessing a quaternary stereocenter in high yields (up to 97 % yield) and excellent enantioselectivities (up to 97 % ee).
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Thioglycoside bond formation
an asymmetric sulfa-Michael/aldol reaction of (
)-β-nucleobase acrylketones and 1,4-dithiane-2,5-diol has been achieved with a cinchona alkaloid-derived bifunctional ...squaramide chiral catalyst. Diverse purine, benzimidazole, and imidazole substrates are well tolerated and generate 4'-thionucleoside derivatives containing three contiguous stereogenic centers with excellent results (30 examples, up to 97% yield, >20 : 1 dr and up to 99% ee). Moreover, the novel strategy provides an efficient and convenient synthetic route to construct chiral 4'-thionucleosides.
A novel concept that conversion of chiral 2-substituted DMAP into its DMAP-N-oxide could significantly enhance the catalytic activity and still be used as an acyl transfer catalyst is presented. A ...new type of chiral 2-substituted DMAP-N-oxides, derived from l-prolinamides, has been rationally designed, facilely synthesized, and applied in the dynamic kinetic resolution of azlactones. Using simple MeOH as the nucleophile, various l-amino acid derivatives were produced in high yields (up to 98% yield) and enantioselectivities (up to 96% ee). Furthermore, α-deuterium labeled l-phenylalanine derivative was also obtained. Experiments and DFT calculations revealed that in 2-substituted DMAP-N-oxide, the oxygen atom acted as the nucleophilic site and the N–H bond functioned as the H-bond donor. High enantioselectivity of the reaction was governed by steric factors, and the addition of benzoic acid reduced the activation energy by participating in the construction of a H-bond bridge. The theoretical chemical study indicated that only when attack directions of the chiral catalyst were fully considered could the correct calculation results be obtained. This work paves the way for the utilization of the C2 position of the pyridine ring and the development of chiral 2-substituted DMAP-N-oxides as efficient acyl transfer catalysts.
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IJS, KILJ, NUK, PNG, UL, UM
The phosphine-catalyzed asymmetric dearomative 3+2 cycloaddition of 2-nitrobenzofurans with aldehyde-derived Morita-Baylis-Hillman (MBH) carbonates or allenoate was developed. The reaction with MBH ...carbonates resulted in a series of cyclopentabenzofurans containing three contiguous stereocenters with good to high yields, diastereoselectivities and enantioselectivities. The use of allenoate also gave the target product with moderate enantioselectivity.
The phosphine-catalyzed asymmetric dearomative 3+2 cycloaddition of 2-nitrobenzofurans with aldehyde-derived MBH carbonates or allenoates was developed.
Described is a facile helix‐nucleating template based on a tethered aspartic acid at the N‐terminus terminal aspartic acid (TD). The nucleating effect of the template is subtly influenced by the ...substituent at the end of the side‐chain‐end tether as indicated by circular dichroism, nuclear magnetic resonance, and molecular dynamics simulations. Unlike most nucleating strategies, the N‐terminal amine is preserved, thus enabling further modification. Peptidomimetic estrogen receptor modulators (PERMs) constructed using this strategy show improved therapeutic properties. The current strategy can be regarded as a good complement to existing helix‐stabilizing methods.
The nucleating effect of the template is subtly influenced by substitution tuning on the side‐chain‐end tether. Unlike most nucleating strategies, the N‐terminal NH2 is preserved, thus enabling further modification. Peptidomimetic estrogen receptor modulators constructed with this method show improved therapeutic properties. Dap=2,3‐diaminopropionic acid.
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