Enantioseparation of 3-phenyllactic acid by chiral ligand exchange countercurrent chromatography.

3-Phenyllactic acid is an antimicrobial compound with broad-spectrum activity against various bacteria and fungus. The observed difference in pharmacological activity between optical isomeric 3-phenyllactic acid necessitates a method for enantioseparation. Chiral ligand exchange countercurrent chromatography was investigated for the enantioseparation of 3-phenyllactic acid with a synthesized chiral ligand. A two-phase solvent system was composed of n-butanol/hexane/water (0.4:0.6:1, v/v/v) to which N-n-dodecyl-l-hydroxyproline was added to the organic phase as chiral ligand and cupric acetate was added in the aqueous phase as a transitional metal ion. The influence factors were optimized by enantioselective liquid-liquid extraction. Baseline enantioseparation of racemic 3-phenyllactic acid by analytical high-speed countercurrent chromatography was achieved. The optical purities of enantiomeric 3-phenyllactic acid reached 99.0%, as determined by chiral high-performance liquid chromatography.

Modeling the retention mechanism for high-performance liquid chromatography with a chiral ligand mobile phase and enantioseparation of mandelic acid derivatives.

The chromatographic retention mechanism describing relationship between retention factor and concentration of Cu(2+) (l-phenylalanine)2 using chiral ligand mobile phase was investigated and eight mandelic acid derivatives were enantioseparated by chiral ligand exchange chromatography. The relationship between retention factor and concentration of the Cu(2+) (l-phenylalanine)2 complex was proven to be in conformity with chromatographic retention mechanism in which chiral discrimination occurred both in mobile and stationary phase. Different copper(II) salts, chiral ligands, organic modifier, pH of aqueous phase, and conventional temperature on retention behavior were optimized. Eight racemates were successfully enantioseparated on a common reversed-phase column with an optimized mobile phase composed of 6 mmol/L of l-phenylalanine or N,N-dimethyl-l-phenylalanine and 3 mmol/Lof copper(II) acetate or copper(II) sulfate aqueous solution and methanol.

Characterization and resistance mechanism of phage-resistant strains of Salmonella enteritidis.

In the face of the increasingly severe problem of antibiotic resistance, phage therapy is regarded as a highly potential alternative. Compared with traditional antimicrobial agents, a key research area of phage therapy is the study of phage-resistant mutant bacteria. To effectively monitor and prevent this resistance, it is crucial to conduct in-depth exploration of the mechanism behind phage resistance. In this study, a strain of Salmonella enteritidis (sm140) and the corresponding phage (Psm140) were isolated from chicken liver and sewage, respectively. Using the double-layer plate method, successfully screened out phage-resistant mutant strains. Whole-genome resequencing of 3 resistant strains found that the wbaP gene of all 3 strains had mutations at a specific position (1,118), with the base changing from G to A. This mutation causes the gene-encoded glycine to be replaced by aspartic acid. Subsequent studies found that the frequency of this gene mutation is extremely high, reaching 84%, and all mutations occur at the same position. To further explore the relationship between the wbaP gene and phage resistance, knockout strains and complement strains of the wbaP gene were constructed. The experimental results confirmed the association between the wbaP gene and phage resistance. At the same time, biological characteristics and virulence were evaluated for wild strains, resistant strains, knockout strains, and complement strains. It was found that mutations or deletions of the wbaP gene lead to a decrease in bacterial environmental adaptability and virulence. Through systematic research on the mechanism and biological characteristics of phage resistance, this study provides important references and guidance for the development of new phage therapies, promoting progress in the field of antimicrobial treatment. At the same time, the emergence of phage resistance due to wbaP gene mutations is reported for the first time in salmonella, providing a new perspective and ideas for further studying phage resistance mechanisms.

LysZX4-NCA, a new endolysin with broad-spectrum antibacterial activity for topical treatment.

The prevalence of multidrug-resistant highly virulent Klebsiella pneumoniae (MDR-hvKP) requires the development of new therapeutic agents. Herein, a novel lytic phage vB_KpnS_ZX4 against MDR-hvKP was discovered in hospital sewage. Phage vB_KpnS_ZX4 had a short latent period (5 min) and a large burst size (230 PFU/cell). It can rapidly reduce the number of bacteria in vitro and improve survival rates of bacteremic mice in vivo from 0 to 80 % with a single injection of 108 PFU. LysZX4, an endolysin derived from vB_KpnS_ZX4, exhibits potent antimicrobial activity in vitro in combination with ethylenediaminetetraacetic acid (EDTA). The antimicrobial activity of LysZX4 was further enhanced by the fusion of KWKLFKI residues from cecropin A (LysZX4-NCA). In vitro antibacterial experiments showed that LysZX4-NCA exerts broad-spectrum antibacterial activity against clinical Gram-negative bacteria, including MDR-hvKP. Moreover, in the mouse model of MDR-hvKP skin infection, treatment with LysZX4-NCA resulted in a three-log reduction in bacterial burden on the skin compared to the control group. Therefore, the novel phages vB_KpnS_ZX4 and LysZX4-NCA are effective reagents for the treatment of systemic and local MDR-hvKP infections.

Preparative enantioseparation of propafenone by counter-current chromatography using di-n-butyl L-tartrate combined with boric acid as the chiral selector.

This paper extends the research of the utilization of borate coordination complexes in chiral separation by counter-current chromatography (CCC). Racemic propafenone was successfully enantioseparated by CCC with di-n-butyl l-tartrate combined with boric acid as the chiral selector. The two-phase solvent system was composed of chloroform/ 0.05 mol/L acetate buffer pH 3.4 containing 0.10 mol/L boric acid (1:1, v/v), in which 0.10 mol/L di-n-butyl l-tartrate was added in the organic phase. The influence of factors in the enantioseparation of propafenone were investigated and optimized. A total of 92 mg of racemic propafenone was completely enantioseparated using high-speed CCC in a single run, yielding 40-42 mg of (R)- and (S)-propafenone enantiomers with an HPLC purity over 90-95%. The recovery for propafenone enantiomers from fractions of CCC was in the range of 85-90%.

Chiral ligand exchange countercurrent chromatography: Equilibrium model study on enantioseparation of mandelic acid.

The equilibrium model in enantioseparation of mandelic acid by chiral ligand exchange countercurrent chromatography was investigated using N-n-dodecyl-l-proline as chiral ligand and cupric ion as central metal. Important parameters, including physical partition coefficient and formation constants of binary and ternary coordination complexes in the two-phase solvent system, were determined. This equilibrium model could give an excellent prediction of distribution ratio and enantioseparation factor of the analyte in the biphasic solvent system, which was further verified by experiments. All the average relative deviations were less than 12%, indicating that the established model could provide a simple computational approach for optimization of enantioseparation conditions in chiral ligand exchange countercurrent chromatography.

Application and comparison of high-speed countercurrent chromatography and high performance liquid chromatography in preparative enantioseparation of α-substitution mandelic acids.

Preparative enantioseparations of α-cyclopentylmandelic acid and α-methylmandelic acid by high-speed countercurrent chromatography (HSCCC) and high performance liquid chromatography (HPLC) were compared using hydroxypropy-ß-cyclodextrin (HP-ß-CD) and sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD) as the chiral mobile phase additives. In preparative HPLC the enantioseparation was achieved on the ODS C18 reverse phase column with the mobile phase composed of a mixture of acetonitrile and 0.10 mol L-1 phosphate buffer at pH 2.68 containing 20 mmol L-1 HP-ß-CD for α-cyclopentylmandelic acid and 20 mmol L-1 SBE-ß-CD for α-methylmandelic acid. The maximum sample size for α-cyclopentylmandelic acid and α-methylmandelic acid was only about 10 mg and 5 mg, respectively. In preparative HSCCC the enantioseparations of these two racemates were performed with the two-phase solvent system composed of n-hexane-methyl tert.-butyl ether-0.1 molL-1 phosphate buffer solution at pH 2.67 containing 0.1 mol L-1 HP-ß-CD for α-cyclopentylmandelic acid (8.5:1.5:10, v/v/v) and 0.1 mol L-1 SBE-ß-CD for α-methylmandelic acid (3:7:10, v/v/v). Under the optimum separation conditions, total 250 mg of racemic α-cyclopentylmandelic acid could be completely enantioseparated by HSCCC with HP-ß-CD as a chiral mobile phase additive in a single run, yielding 105-110 mg of enantiomers with 95-98% purity and 85-90% recovery. But, no complete enantioseparation of α-methylmandelic acid was achieved by preparative HSCCC with either of the chiral selectors due to their limited enantioselectivity. In this paper preparative enantioseparation by HSCCC and HPLC was compared from various aspects.

[High performance liquid chromatographic enantioseparation of atrolactic acids using chiral mobile phase additive].

A method was established for the enantioseparation of atrolactic acids using high performance liquid chromatography with sulfobutyl ether-beta-cyclodextrin (SBE-beta-CD) as the chiral mobile phase additive, and a C18 reversed-phase column. The influences of the different types of cyclodextrin derivatives, the concentration of chiral mobile phase additive, pH value of the mobile phase, the flow rate and column temperature on the peak resolution were investigated. The separation mechanism for atrolactic acids by high performance liquid chromatography using chiral mobile phase additive, as well as the formation of inclusion complex between SBE-beta-CD and atrolactic acid was studied. In addition, the formation constant was calculated. The enantioseparation was carried out on a reversed-phase column YMC-Pack ODS-A C18 (250 mm x 4.6 mm, 5 microm) with chiral mobile phase consisted of 0.1 mol/L phosphate buffer at pH 2.68 containing 25 mmol/L SBE-beta-CD-acetonitrile (90:10, v/v). The detection wavelength was 220 nm. The flow rate was 0.6 mL/min and the column temperature was 30 degrees C. The retention times of atrolactic acids were 26.65 and 28.28 min, and the peak resolution of 1.68 was achieved. The above established method proves to be a simple and economical way for analytical enantioseparation of atrolactic acid with high peak resolution.

Enantioseparation of mandelic acid derivatives by high performance liquid chromatography with substituted ß-cyclodextrin as chiral mobile phase additive and evaluation of inclusion complex formation.

The enantioseparation of ten mandelic acid derivatives was performed by reverse phase high performance liquid chromatography with hydroxypropyl-ß-cyclodextrin (HP-ß-CD) or sulfobutyl ether-ß-cyclodextrin (SBE-ß-CD) as chiral mobile phase additives, in which inclusion complex formations between cyclodextrins and enantiomers were evaluated. The effects of various factors such as the composition of mobile phase, concentration of cyclodextrins and column temperature on retention and enantioselectivity were studied. The peak resolutions and retention time of the enantiomers were strongly affected by the pH, the organic modifier and the type of ß-cyclodextrin in the mobile phase, while the concentration of buffer solution and temperature had a relatively low effect on resolutions. Enantioseparations were successfully achieved on a Shimpack CLC-ODS column (150×4.6mm i.d., 5µm). The mobile phase was a mixture of acetonitrile and 0.10molL(-1) of phosphate buffer at pH 2.68 containing 20mmolL(-1) of HP-ß-CD or SBE-ß-CD. Semi-preparative enantioseparation of about 10mg of α-cyclohexylmandelic acid and α-cyclopentylmandelic acid were established individually. Cyclodextrin-enantiomer complex stoichiometries as well as binding constants were investigated. Results showed that stoichiometries for all the inclusion complex of cyclodextrin-enantiomers were 1:1.

Chiral ligand exchange high-speed countercurrent chromatography: mechanism and application in enantioseparation of aromatic α-hydroxyl acids.

This work concentrates on the separation mechanism and application of chiral ligand exchange high-speed countercurrent chromatography in enantioseparation of ten racemic aromatic α-hydroxyl acids, including mandelic acid, 2-chloromandelic acid, 4-methoxymandelic acid, 4-hydroxymandelic acid, α-methylmandelic acid, 4-hydroxy-3-methoxy-mandelic acid, 3-chloromandelic acid, 4-bromomandelic acid, α-cyclopentylmandelic acid and α-cyclohexylmandelic acid, in which five of the racemates were successfully enantioseparated by analytical apparatus with an optimized solvent system. The two-phase solvent system was composed of butanol-water (1:1, v/v) or hexane-n-butanol-water (0.5:0.5:1, v/v), to which N-n-dodecyl-l-proline was added in the organic phase as chiral ligand and cupric acetate was added in the aqueous phase as a transition metal ion. Various influence factors in high-speed countercurrent chromatography were optimized by enantioselective liquid-liquid extraction. The separation mechanism for chiral ligand exchange high-speed countercurrent chromatography was proposed based on the results of present studies. Successful enantioseparations of 72mg of mandelic acid, 76mg of 2-chloromandelic acid and 74mg of 4-methoxymandelic acid were achieved individually with high resolution by preparative high-speed countercurrent chromatography. The HPLC purity of all enantiomers was over 96% with the recovery in the range of 82-90% from the collected fractions.