Enantioselective liquid-liquid extraction of DL-mandelic acid using chiral diphosphine ligands as extractants

Enantioseparation of amino acid and mandelic acid enantiomers using Josiphos-metal complexes as chiral extractants

The development of new and efficient chiral extractants has always been the research hotspot and difficulty in the field of chiral extraction. Josiphos, a famous ferrocene derivative catalyst, is employed as a chiral extractant in enantioseparation of amino acid and mandelic acid enantiomers. The influences of metal ions, organic solvents, pH of the aqueous solution, extractant concentrations, and extraction temperature on enantioselectivities are systematically studied. The result reveals that Josiphos-Pd has good capabilities to enantioseparate 4-nitro-phenylalanine (Nphe), 3-chloro-phenylglycine (Cpheg), and mandelic acid (MA) with separation factors (α) of 3.30, 2.65, and 2.18, respectively. The pH of the aqueous phase and Josiphos-Pd concentration affect the extraction significantly, whereas extraction temperature shows little influence. After optimizing by response surface method, the mathematical models for extractions are established. And the highest experimental performance factors (pf) for Nphe, Cpheg, and MA are 0.1843, 0.1335, and 0.08884, respectively.

Enantioseparation of amino acid and mandelic acid enantiomers using Garphos derivatives as chiral extractants

In this paper, Garphos with different substituents were employed as chiral extractants to enantioseparate racemic amino acid and mandelic acid. The influences of metal precursors, pH of aqueous solution, Garphos-metal concentration, extraction temperature, and substituent effect on extraction were investigated. The results indicated that the substituent groups significantly affected the π-π interaction between extractant and substrate. And the separation factors (α) for Garphos could be remarkably improved by regulating substituent groups. Garphos-II-Pd, Garphos-VI-Pd, Garphos-III-Pd, Garphos-I-Cu, Garphos-VI-Cu, and Garphos-V-Pd were the most efficient extractants for phenylalanine (Phe), homophenylalanine (Hphe), 4-nitrophenylalanine (Nphe), 3-chlorophenylglycine (Cpheg), mandelic acid (MA), and 2-chlormandelic acid (CMA) with α values of 2.40, 2.37, 5.37, 1.59, 5.98, and 3.69, respectively. This work provided an important reference for the design of efficient chiral extractants in future work.

Magnetic Molecularly Imprinted Polymers Based on Dehydroabietylamine as Chiral Monomers for the Enantioseparation of RS-Mandelic Acid

Stereoselective adsorption of the enantiomers shows potential in the resolution of a racemate. In this work, we synthesized novel magnetic surface molecularly imprinted polymers (MIPs) on the surface of the γ-methacryloxypropyltrimethoxysilane (MPS)-modified Fe₃O₄@SiO₂ particles to utilize chiral dehydroabietylamine (DHA) as a functional monomer and R-mandelic acid as a template molecule (DHA-MIPs). We performed the resolution of mandelic acid racemate (RS-MA) via adsorption on the as-prepared MIPs. The results revealed that the MIPs have good affinity and high adsorption capacity for R-MA and show better enantioselective adsorption ability for R-MA than that for S-MA. One-stage adsorption of RS-MA on the MIPs can achieve up to 53.7% enantiomeric excess (ee) for R-MA. These help us to improve the chiral separation ability of the traditional MIPs using a chiral rather than an achiral monomer in MIP preparation. The MIPs can be employed as an economic and efficient adsorbent for chiral separation of MA racemate.

Investigation of Taniaphos as a chiral selector in chiral extraction of amino acid enantiomers

Finding chiral selector with high stereoselectivity to a variety of amino acid enantiomers remains a challenge and warrants further research. In this work, Taniaphos, a chiral ligand with rotatable spatial configuration, was employed as a chiral extractant to enantioseparate various amino acid enantiomers. Phenylalanine (Phe), homophenylalanine (Hphe), 4-nitrophenylalanine (Nphe), and 3-chloro-phenylglycine (Cpheg) were used as substrates to evaluate the extraction efficiency. The results revealed that Taniaphos-Cu exhibited good abilities to enantioseparate Phe, Hphe, Nphe, and Cpheg with the highest separation factors (α) of 3.13, 2.10, 2.32, and 2.14, respectively. Taniaphos-Cu is more conducive to combine with D-amino acid in extraction. The influences of pH, Taniaphos-Cu, and concentration and extraction temperature on extraction were comprehensively evaluated. The highest performance factors (pf) for Phe, Hphe, Nphe, and Cpheg at optimal extraction conditions were 0.08892, 0.1250, 0.09621, and 0.08021, respectively. The recognition mechanism between Taniaphos-Cu and amino acid enantiomers was discussed. The coordination interaction between Taniaphos-Cu and COO^- , π-π interaction between Taniaphos-Cu and amino acid enantiomers are important acting forces in chiral extraction. The steric-hindrance between NH₂ and OH lead to Taniaphos-Cu-D-Phe is more stable than Taniaphos-Cu-L-Phe. This work provided a chiral extractant that has good abilities to enantioseparate various amino acid enantiomers.