Recent Development: Enantioselective Extraction in Chiral Separation

Hashemi M; Hadjmohammadi MR

Review Article

Austin J Anal Pharm Chem. 2021; 8(1): 1130.

Recent Development: Enantioselective Extraction in Chiral Separation

Hashemi M and Hadjmohammadi MR*

Department of Chemistry, University of Mazandaran, Iran

*Corresponding author: Mohammad Reza Hadjmohammadi, Department of Chemistry, University of Mazandaran, Babolsar, Iran

Received: December 31, 2020; Accepted: February 24, 2021; Published: March 03, 2021

Abstract

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.

Keywords: Enantioselective extraction; Chiral separation; Liquid-liquid extraction; Solid phase extraction

Introduction

Chiral compounds exhibit different properties in biochemical systems, even though they are indistinguishable in most inanimate environments [1]. Two enantiomers of a charily active drug may have dramatically different pharmacological effects, and one of two enantiomers of a chiral pollutant/xenobiotic may be more toxic [2]. In the modern pharmaceutical especially in anti-cancer drugs only one enantiomer has medicinal properties and other enantiomer doesn�t have this properties, in other case maybe one enantiomer is useful for body and other one is harmful or it has any effect on body [3]. Noted to this fact that these drugs have harmful effects for body then using racemic mixture for remedy is not effective. Therefore, separation of racemic mixture is necessary for two reasons, one is that harmful effects reduced and other target is economical target, because anticancer drugs are very expensive and using one enantiomer for remedy decreases costs. Hence, there is a great need to develop the technology for analysis and separation of racemic drugs. Current methods of enantiomeric analysis include such non-chromatographic techniques as polarimetry [4], nuclear magnetic resonance [5], isotopic dilution [6], calorimetry [7], and enzyme [8] techniques. The disadvantages of these techniques are the need for pure samples, and no separation of enantiomers is involved. Quantitation, which does not require pure samples, and separation of enantiomers can be done simultaneously by either Gas Chromatography (GC) [9] or High Performance Liquid Chromatography (HPLC) [10]. Chiral HPLC has proven to be one of the best methods for the direct separation and analysis of enantiomers. Chiral separation is often required as the final product purification step after asymmetric synthesis. The two main industrialscale separation methods each have serious drawbacks. Diastereomer crystallization is inflexible and involves solid phase handling [11], and Simulated Moving Bed Chromatography (SMB) is very expensive and produces rather diluted product streams [12]. Therefore, there is a need for a flexible cost-effective separation method suitable for the commercial production scale. Extraction methods are effective, cheep, and flexible method in small and big scale for chiral separation. Chiral selectors play the most important role in the separation efficiency of all enantiomer separation Techniques [13]. In enantioselective extraction, an enantiopure host is used as a chiral selector to bind enantiospecifically and reversibly with a racemic substrate. The enantiomer that a complex most strongly with the chiral selector is recovered from the extract and the other enantiomer remains in the initial balk. If the host is confined to one phase in a biphasic system, an enantiomeric separation of the substrate can take place between the two phases in a single step. If the separation is imperfect, a fractional extraction series is required. In this, review we intend to introduce extraction methods that used in chiral separation in the past, and in the end of we will compare these methods together in discussion part.

Liquid-Liquid Extraction

Liquid-liquid extraction is a commonly used method to extract and separate compounds based on their relative solubilities in two immiscible phases, usually an aqueous phase and an organic solvent phase. It is an extraction of a substance from one liquid into another liquid phase.

Enantioselective liquid-liquid extraction

In the enantioselective liquid-liquid extraction, usually chiral selectors were dissolved in the organic solvent, and racemic mixture was dissolved in the aqueous phase. Two phases were mixed sufficiently, and (S)-chiral selector and (R)-chiral selector complexes distributed differently in the water phase and the organic phase, respectively. chiral selectors have different chiral recognition abilities of the (R)-form and (S)-form of analyt. As a result, the desired one enantiomer was rich in the organic phase and other enantiomer was rich in the water phase, which allowed a separation of (R) and (S) to some extent.

Calculation of distribution ratio and selectivity: The extent of extraction is characterized by the distribution ratios DR and DS for each enantiomer:

D_{R} = \frac{[R] org allforms}{[R] a q allforms}

Recent Development: Enantioselective Extraction in Chiral Separation

Abstract

Introduction

Liquid-Liquid Extraction

Enantioselective liquid-liquid extraction

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

Abstract

References