Preparation of Novel Chiral Stationary Phases Based on the Chiral Porous Organic Cage by Thiol-ene Click Chemistry for Enantioseparation in HPLC.

Porous organic cages (POCs) are an emerging class of porous materials that have aroused considerable research interest because of their unique characteristics, including good solubility and a well-defined intrinsic cavity. However, there have so far been no reports of chiral POCs as chiral stationary phases (CSPs) for enantioseparation by high-performance liquid chromatography (HPLC). Herein, we report the first immobilization of a chiral POC, NC1-R, on thiol-functionalized silica using a mild thiol-ene click reaction to prepare novel CSPs for HPLC. Two CSPs (CSP-1 and CSP-2) with different spacers have been prepared. CSP-1, with a cationic imidazolium spacer, exhibited excellent enantioselectivity for the resolution of various racemates. Twenty-three and 12 racemic compounds or chiral drugs were well enantioseparated on the CSP-1-packed column under normal-phase and reversed-phase conditions, respectively, including alcohols, diols, esters, ethers, ketones, epoxides, organic acids, and amines. In contrast, chiral resolution using CSP-2 (without a cationic imidazolium spacer)-packed column B was inferior to that of column A, demonstrating the important role of the cationic imidazolium spacer for chiral separation. The chiral separation capability of column A was also compared with that of two most popular commercial chiral columns, Chiralpak AD-H and Chiralcel OD-H, which exhibits good chiral recognition complementarity with the two commercial chiral columns. In addition, five positional isomers dinitrobenzene, nitroaniline, chloroaniline, bromoaniline, and iodoaniline were also well separated on column A. The effects of temperature, mobile phase composition, and injected analyte mass for separation on column A were investigated. Column A also showed good stability and reproducibility after repeated injections. This work demonstrates that chiral POCs are promising chiral materials for HPLC enantioseparation.

Preparation of chiral stationary phase based on a [3+3] chiral polyimine macrocycle by thiol-ene click chemistry for enantioseparation in normal-phase and reversed-phase high performance liquid chromatography.

Polyimine macrocycles are a new class of organic macrocycles with cyclic structures, well-defined molecular cavities, and multiple cooperative binding sites, which have recently aroused considerable research interest in molecular recognition and separation. Herein, we report the bonding of a [3+3] chiral polyimine macrocycle (H3L, C78H78N6O3) on thiol-functionalized silica gel using thiol-ene click chemistry to prepare a chiral stationary phase (CSP) for high performance liquid chromatography (HPLC). The fabricated column exhibited excellent chiral separation capability under both normal-phase and reversed-phase conditions. Fourteen and 10 racemates were well resolved on the column in normal-phase mode (using n-hexane/isopropanol as the mobile phase) and reversed-phase mode (using methanol/water as the mobile phase), respectively, including alcohols, esters, ethers, ketones, aldehydes, epoxides and organic acids. Moreover, the column also shows good selectivity toward positional isomers. Six positional isomers (dinitrobenzene, chloroaniline, bromoaniline, iodoaniline, nitrobrobenzene and nitrochlorobenzene) were well separated on the column. In addition, the effects of the injection mass and mobile phase composition on the separation were investigated. The column shows good reproducibility and stability after multiple injections with the relative standard deviation (RSD) (n = 5) of the retention time and resolution being < 0.96 % and 0.65 %, respectively. This study indicates that this type of chiral polyimine macrocycles is a promising chiral selector for HPLC enantioseparation and will push forward the applications of more novel chiral macrocycles for chiral chromatographic separation.

"Click" preparation of a chiral macrocycle-based stationary phase for both normal-phase and reversed-phase high performance liquid chromatography enantioseparation.

Chiral polyimine macrocycles (CPMs) constitute a new family of organic macrocycles that have defined cavities, rigid shapes, inherent chirality and multiple cooperative binding sites, and have shown great potential in diverse areas. However, the application of CPMs for high performance liquid chromatography (HPLC) enantioseparation has rarely been reported. In this work, a novel chiral stationary phase (CSP) for HPLC was prepared by chemical bonding of a CPM (C54H72N6O3) onto thiolated silica via thiol-ene click reaction. The CSP exhibited good enantioselectivity in both normal- and reversed-phase HPLC. Chiral compounds included alcohols, diols, ketones, organic acids, esters, ethers, amines, and epoxides were enantioseparated on the column in normal-phase mode (17 compounds) and reversed-phase mode (20 compounds). Importantly, broader chiral resolution was observed with the column than that obtained using our previously studied chiral macrocycle H3L-based column, indicating the potential to significantly improve and broaden applicability of this novel macrocycle-type CSPs. Moreover, the CSP exhibited good complementary enantioseparation to Chiralpak AD-H and Chiralcel OD-H columns, enabling separation of some racemates that could not be separated by the two popular chiral HPLC columns. In addition, the fabricated column exhibited good stability and reproducibility. The relative standard deviations (RSDs) (n = 5) of retention time and resolution after multiple injections were < 0.20 % and < 0.39 %, respectively. The results demonstrated the great potential of this type of CPM for HPLC separation of enantiomers.

Preparation and evaluation of a chiral porous organic cage based chiral stationary phase for enantioseparation in high performance liquid chromatography.

Porous organic cages (POCs) are a new kind of porous molecular materials, which have gained widespread interest in many fields due to their intriguing properties, including excellent molecular solubility, inherent molecular cavity and rich host-guest chemistry. To date, many chiral POCs have been explored as chiral stationary phases (CSPs) for gas chromatographic (GC) separation of enantiomers. However, the applications of chiral POCs for high performance liquid chromatography (HPLC) enantiomeric separation is extremely rare. In this study, we report the construction of thiol-ene click reaction for the preparation of CSP for HPLC by using a [4+8]-type chiral POC NC4-R as chiral selector. The fabricated CSP showed good chiral resolution performance not only in normal-phase HPLC (NP-HPLC) but also in reversed-phase HPLC (RP-HPLC). Seventeen and ten racemates were well resolved in the two separation modes, respectively, including ketones, esters, alcohols, phenols, amines, ethers, organic acids, and amino acids. Moreover, the fabricated column also shows good chiral recognition complementarity to two popular chiral HPLC columns (Chiralpak AD-H and Chiralcel OD-H columns) and previously reported chiral POC NC1-R-based HPLC column, which can resolve some racemates that unable to be resolved by the two commercially available chiral HPLC columns and NC1-R-based column. The relative standard deviation (RSD) values (n = 4) of retention time and resolution (Rs) of analytes separated on the column were less than 0.3 % and 0.5 % after it was subjected to different injections, showing the good reproducibility and stability of the NC4-R-based column. This work demonstrated high potentials of chiral POCs for HPLC enantioseparation and the applicability of chiral POC-based HPLC columns can be broadened by developing more chiral POCs with diverse structures as chiral selector for HPLC.

Diosgenin exerts an antihypertensive effect in spontaneously hypertensive rats via gut-brain communication.

Gut microbiota is well-established to regulate host blood pressure. Diosgenin is a natural steroid sapogenin with documented anti-inflammatory, antioxidant and antihypertensive properties. We aimed to investigate whether the antihypertensive effects of diosgenin are mediated by the microbiota-gut-brain axis in spontaneously hypertensive rats (SHR). 15-Week-old male Wistar Kyoto rats (WKY) and age-matched SHR were randomly distributed into three groups: WKY, SHR treated with a vehicle, and SHR treated with diosgenin (100 mg kg-1). Our results showed that diosgenin prevented elevated systolic blood pressure (SBP) and ameliorated cardiac hypertrophy in SHR. Moreover, the gut microbiota composition and intestinal integrity were improved. Furthermore, increased butyrate-producing bacteria and plasma butyrate and decreased plasma lipopolysaccharides were observed in SHR treated with diosgenin. These findings were associated with reduced microglial activation and neuroinflammation in the paraventricular nucleus. Our findings suggest that diosgenin attenuates hypertension by reshaping the gut microbiota and improving the gut-brain axis.