Recent Development: Enantioselective Extraction in Chiral Separation

This paper discusses the recent development of enantioselective extraction methods. There are several methods in this field. The principles of all of enantioselective extraction methods are presented a focus on twophase extractions, in these methods used a chiral compound that named chiral selector, this compound distinguishes between two chiral isomers in complexation process, then one isomer more captured by chiral selector, and separation processes happen. The chiral selector should dissolve in on phase. In these methods, typical performance data are reported major emphasis on distribution ratio and enantioselectivity value or selectivity factor. In this paper, we introduce types of enantioselective extraction method, and discuss about them with several examples.

Recent Development: Enantio Selective Eextraction in Chiral Separation

This paper discusses the recent development of enantioselective extraction methods. There are several methods in this field. The principles of all of enantioselective extraction methods are presented a focus on twophase extractions, in these methods used a chiral compound that named chiral selector, this compound distinguishes between two chiral isomers in complexation process, then one isomer more captured by chiral selector, and separation processes happen. The chiral selector should dissolve in on phase. In these methods, typical performance data are reported major emphasis on distribution ratio and enantioselectivity value or selectivity factor. In this paper, we introduce types of enantioselective extraction method, and discuss about them with several examples.

Enantioselective extraction of unprotected amino acids coupled with racemization

Scalable and economical methods for the production of optically pure amino acids, both natural and unnatural, are essential for their use as synthetic building blocks. Currently, enzymatic dynamic kinetic resolution (DKR) underpins some of the most effective processes. Here we report the development of enantioselective extraction coupled with racemization (EECR) for the chirality conversion of underivatized amino acids. In this process, the catalytic racemization of amino acids in a basic aqueous solution is coupled with the selective extraction of one enantiomer into an organic layer. Back-extraction from the organic layer to an acidic aqueous solution then completes the deracemization of the amino acid. The automation of the EECR process in a recycling flow reactor is also demonstrated. Continuous EECR is made possible by the sterically hindered chiral ketone extractant 5, which prevents the coextraction of the copper racemization catalyst because of its nonplanar geometry. Furthermore, the extractant 5 unexpectedly forms imines with amino acids faster and with greater enantioselectivity than less bulky derivatives, even though 5 cannot participate in intramolecular resonance-assisted hydrogen bonding. These features may allow EECR to challenge the preponderance of enzymatic DKR in the production of enantiomerically enriched amino acids.

Enantioselective Extraction of Phenylalanine Enantiomers Using Environmentally Friendly Aqueous Two-Phase Systems

(1) Background: The environmentally friendly choline-amino acid ionic liquids (ChAAILs) and deep eutectic solvents (DESs) have been used as excellent alternatives to volatile organic compounds (VOCs) and ionic liquids (ILs) in recent years; (2) Methods: Thus, ChAAILs/salt and DESs/salt aqueous two-phase systems (ATPSs) were developed for the chiral extraction of phenylalanine enantiomers. The optimum ATPS of [Ch][L-Pro]/K3PO4 was chosen, and the influencing parameters were investigated, including ChAAILs concentration, salt concentration, chiral selector concentration, extraction temperature, phenylalanine concentration, and system pH; (3) Results: The phenylalanine enantiomers were mainly extracted into the top phase (ChAAIL-rich phase), meanwhile, the (S)-phenylalanine [(S)-Phe)] was preferentially recognized by the chiral selector in the top phase. The maximum separation factor (α) of 2.05 was obtained under the optimal conditions; and (4) Conclusions: This ATPS that was used for the chiral extraction of enantiomers is much more environmentally friendly, simple, and rapid, and has the potential to be used in the enantioselective extraction of other enantiomers.

A molecular receptor selective for zwitterionic alanine

A new chiral chromane receptor has been synthesized with a right-sized oxyanion hole to fix zwitterionic alanine. This associate allows the enantioselective extraction of this amino acid from water to chloroform.

A highly selective receptor for zwitterionic proline

Enantioselective extraction of zwitterionic proline from water to chloroform has been achieved with a chiral apolar chromane receptor.