High-Enantioselectivity Adsorption Separation of Racemic Mandelic Acid and Methyl Mandelate by Robust Chiral UiO-68-Type Zr-MOFs

Mandelic acid and its analogues are highly valuable medical intermediates and play an important role in the pharmaceutical industry, biochemistry, and life sciences. Therefore, effective enantioselective recognition and separation of mandelic acid are of great significance. In this study, two of our recently reported chiral amine-alcohol-functionalized UiO-68-type Zr-HMOFs 1 and 3 with high chemical stability, abundant binding sites, and large chiral pores were selected as chiral selectors for the enantioselective separation of mandelic acid (MA), methyl mandelate (MM), and other chiral molecules containing only one phenyl. Materials 1 and 3 exhibited excellent enantioselective separation performance for MA and MM. Especially for the separation of racemate MA, the enantiomeric excess values reached 97.3 and 98.9%, which are the highest reported values so far. Experimental and density functional theory (DFT) computational results demonstrated that the introduction of additional phenyls on the chiral amine alcohol pendants in 3 had somewhat impact on the enantioselective adsorption and separation of MA or MM compared with 1, but it was not significant. Further research on the enantioselective separation of those chiral adsorbates containing only one phenyl by material 1 indicated the crucial role of the groups directly bonded to the chiral carbons of the adsorbates in the selective separation of enantiomers, especially showing higher enantioselectivity for the adsorbates with two hydrogen-bonding groups directly bonded to its chiral carbon.

Design, Synthesis, In Vitro Antifungal Activity and Mechanism Study of the Novel 4-Substituted Mandelic Acid Derivatives

Plant diseases caused by phytopathogenic fungi are a serious threat in the process of crop production and cause large economic losses to global agriculture. To obtain high-antifungal-activity compounds with novel action mechanisms, a series of 4-substituted mandelic acid derivatives containing a 1,3,4-oxadiazole moiety were designed and synthesized. In vitro bioassay results revealed that some compounds exhibited excellent activity against the tested fungi. Among them, the EC₅₀ values of E₁₃ against Gibberella saubinetii (G. saubinetii), E₆ against Verticillium dahlia (V. dahlia), and E₁₈ against Sclerotinia sclerotiorum (S. sclerotiorum) were 20.4, 12.7, and 8.0 mg/L, respectively, which were highly superior to that of the commercialized fungicide mandipropamid. The morphological studies of G. saubinetii with a fluorescence microscope (FM) and scanning electron microscope (SEM) indicated that E₁₃ broke the surface of the hyphae and destroyed cell membrane integrity with increased concentration, thereby inhibiting fungal reproduction. Further cytoplasmic content leakage determination results showed a dramatic increase of the nucleic acid and protein concentrations in mycelia with E₁₃ treatment, which also indicated that the title compound E₁₃ could destroy cell membrane integrity and affect the growth of fungi. These results provide important information for further study of the mechanism of action of mandelic acid derivatives and their structural derivatization.

Synthesis, Antifungal Evaluation, 3D-QSAR, and Preliminarily Mechanism Study of Novel Chiral Mandelic Acid Derivatives

To investigate the effect of spatial configuration on the biological activity of the compounds, a series of chiral mandelic acid derivatives with a moiety of 1,3,4-oxadiazole thioether have been designed and synthesized. Bioassay results demonstrated that most title compounds with the S-configuration exhibited better in vitro antifungal activity against three plant fungi, such as H3' (EC₅₀ = 19.3 μg/mL) against Gibberella saubinetii, which was approximately 16 times higher than that of H3 (EC₅₀ = 317.0 μg/mL). CoMFA and CoMSIA models were established for 3D-QSAR analysis and provided an important support for further optimization of this series of compounds. Comparing the preliminary mechanism studies between enantiomers (H3 and H3') found that the S-configuration compound (H3') exhibited a stronger ability to destroy the surface structure of G. saubinetii mycelia, causing the leakage of intracellular substances to accelerate and the growth of the hyphae to be inhibited. The results provided a novel view for the further optimization of this series of active compounds and deep mechanism study of chiral pesticides.

Circularly Polarized Light-Driven Supramolecular Chirality

Introduction of asymmetry into a supramolecular system via external chiral stimuli can contribute to the understanding of the intriguing homochirality found in nature. Circularly polarized light (CPL) is regarded as a chiral physical force with right- or left-handedness. It can induce and modulate supramolecular chirality due to preferential interaction with one enantiomer. Herein, this review focuses on the photon-to-matter chirality transfer mechanisms at the supramolecular level. Thus, asymmetric photochemical reactions are reviewed, and the creation of a chiral bias upon CPL irradiation is discussed. Furthermore, the possible mechanisms for the amplification and propagation of the bias into the supramolecular level are outlined based on the nature of the photochromic building block. Representative examples, including azobenzene derivatives, polydiacetylene, bicyclic ketone, polyfluorenes, C_n -symmetric molecules, and inorganic nanomaterials, are presented.

Preparation of a polydopamine/β-cyclodextrin coated open tubular capillary electrochromatography column and application for enantioseparation of five proton pump inhibitors

An open tubular capillary electrochromatography column was prepared by immobilizing β-cyclodextrin on the inner wall of pretreated capillary via noncovalent adsorption of polydopamine. The resulting coating layer on the capillary was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Electroosmotic flow was studied to evaluate the variation of the immobilized columns. The prepared columns showed good chiral separation performance toward five proton pump inhibitors including lansoprazole, pantoprazole, tenatoprazole, rabeprazole, and omeprazole. The influences of β-cyclodextrin concentration, coating time, buffer pH, buffer concentration, and applied voltage on separation were investigated. In the optimum conditions, the enantiomers of five analytes were fully resolved within 15 min with high resolutions of 4.57 to 8.13. The method was extensively validated in terms of accuracy, precision, and linearity and proved to be robust. The relative standard deviation values for migration times and peak areas of the analytes representing intraday and interday were less than 1.9 and 3.6%, respectively. Further, the polydopamine/β-cyclodextrin coated capillary column could be successively used over 100 runs without showing significant decrease in the separation efficiency.

Design, synthesis and antifungal evaluation of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety

A series of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassay results showed that some target compounds exhibited certain antifungal activity against six kinds of pathogenic fungi in vitro. Among the compounds, the EC₅₀ values of T₄₁ against Gibberella saubinetii, Verticillium dahlia and Sclerotinia sclerotiorum were 31.0, 27.0 and 32.1 μg/ml, respectively, and the EC₅₀ value of T₁₄ against S. sclerotiorum was 14.7 μg/ml. The antifungal activity against the resistant fungus S. sclerotiorum indicated that this series of target compounds may have the similar action modes or sites as the commercialized succinate dehydrogenase inhibitor carboxin. A morphological study with fluorescence microscope demonstrated that T₄₁ can significantly destroy the membrane integrity of G. saubinetii.

The Chirality Induction and Modulation of Polymers by Circularly Polarized Light

Chirality is a natural attribute nature of living matter and plays an important role in maintaining the metabolism, evolution and functional activities of living organisms. Asymmetric conformation represents the chiral structure of biomacromolecules in living organisms on earth, such as the L-amino acids of proteins and enzymes, and the D-sugars of DNA or RNA, which exist preferentially as one enantiomer. Circularly polarized light (CPL), observed in the formation regions of the Orion constellation, has long been proposed as one of the origins of single chirality. Herein, the CPL triggered asymmetric polymerization, photo-modulation of chirality based on polymers are described. The mechanisms between CPL and polymers (including polydiacetylene, azobenzene polymers, chiral coordination polymers, and polyfluorene) are described in detail. This minireview provides a promising flexible asymmetric synthesis method for the fabrication of chiral polymer via CPL irradiation, with the hope of obtaining a better understanding of the origin of homochirality on earth.

Chiral lipidomics of monoepoxy and monohydroxy metabolites derived from long-chain polyunsaturated fatty acids

A chiral lipidomics approach was established for comprehensive profiling of regio- and stereoisomeric monoepoxy and monohydroxy metabolites of long-chain PUFAs as generated enzymatically by cytochromes P450 (CYPs), lipoxygenases (LOXs), and cyclooxygenases (COXs) and, in part, also unspecific oxidations. The method relies on reversed-phase chiral-LC coupled with ESI/MS/MS. Applications revealed partially opposing enantioselectivities of soluble and microsomal epoxide hydrolases (mEHs). Ablation of the soluble epoxide hydrolase (sEH) gene resulted in specific alterations in the enantiomeric composition of endogenous monoepoxy metabolites. For example, the (R,S)/(S,R)-ratio of circulating 14,15-EET changed from 2.1:1 in WT to 9.7:1 in the sEH-KO mice. Studies with liver microsomes suggested that CYP/mEH interactions play a primary role in determining the enantiomeric composition of monoepoxy metabolites during their generation and release from the ER. Analysis of human plasma showed significant enantiomeric excess with several monoepoxy metabolites. Monohydroxy metabolites were generally present as racemates; however, Ca2+-ionophore stimulation of whole blood samples resulted in enantioselective increases of LOX-derived metabolites (12S-HETE and 17S-hydroxydocosahexaenoic acid) and COX-derived metabolites (11R-HETE). Our chiral approach may provide novel opportunities for investigating the role of bioactive lipid mediators that generally exert their physiological functions in a highly regio- and stereospecific manner.