enantiomeric separation
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Separations ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 7
Author(s):  
Isabella Bolognino ◽  
Antonio Carrieri ◽  
Rosa Purgatorio ◽  
Marco Catto ◽  
Rocco Caliandro ◽  
...  

The enantiomeric separation of 15 racemic 4-aryl-3,4-dihydropyrimidin-2(1H)-one (DHP) alkoxycarbonyl esters, some of which proved to be highly active as A2B adenosine receptor antagonists, was carried out by HPLC on ChirobioticTM TAG, a chiral stationary phase (CSP) bearing teicoplanin aglycone (TAG) as the chiral selector. The racemic compounds were separated under polar organic (PO) conditions. Preliminarily, the same selectands were investigated on three different Pirkle-type CSPs in normal-phase (NP) conditions. A baseline separation was successfully obtained on TAG-based CSPs for the majority of compounds, some of which achieved high enantioselectivity ratios (α > 2) in contrast with the smaller α values (1–1.5) and the lack of baseline resolution observed with the Pirkle-type CSPs. In particular, the racemic tetrazole-fused DHP ester derivatives, namely compounds 8 and 9, were separated on TAG-based HPLC columns with noteworthy α values (8.8 and 6.0, respectively), demonstrating the potential of the method for preparative purposes. A competition experiment, carried out with a racemic analyte (6) by adding N-acetyl-d-alanine (NADA) to the mobile phase, suggested that H-bonding interactions involved in the recognition of the natural dipeptide ligand d-Ala-d-Ala into the TAG cleft should be critical for enantioselective recognition of 4-aryl DHPs by TAG. The X-ray crystal structure of TAG was elucidated at a 0.77 Å resolution, whereas the calculation of molecular descriptors of size, polar, and H-bond interactions, were complemented with molecular docking and molecular dynamics calculations, shedding light on repulsive (steric effects) and attractive (H-bond—polar and apolar) interactions between 4-aryl DHP selectands and TAG chiral selectors.


Molecules ◽  
2021 ◽  
Vol 26 (23) ◽  
pp. 7288
Author(s):  
Basma Saleh ◽  
Tongyan Ding ◽  
Yuwei Wang ◽  
Xiantong Zheng ◽  
Rong Liu ◽  
...  

Closantel is an antiparasitic drug marketed in a racemic form with one chiral center. It is meaningful to develop a method for separating and analyzing the closantel enantiomers. In this work, two enantiomeric separation methods of closantel were explored by normal-phase high-performance liquid chromatography. The influences of the chiral stationary phase (CSP) structure, the mobile phase composition, the nature and proportion of different mobile phase modifiers (alcohols and acids), and the column temperature on the enantiomeric separation of closantel were investigated in detail. The two enantiomers were successfully separated on the novel CSP of isopropyl derivatives of cyclofructan 6 and n-hexane-isopropanol-trifluoroacetic acid (97:3:0.1, v/v/v) as a mobile phase with a resolution (Rs) of about 2.48. The enantiomers were also well separated on the CSP of tris-carbamates of amylose with a higher Rs (about 3.79) when a mixture of n-hexane-isopropanol-trifluoroacetic acid (55:45:0.1, v/v/v) was used as mobile phase. Thus, the proposed separation methods can facilitate molecular pharmacological and biological research on closantel and its enantiomers.


2021 ◽  
Author(s):  
Anderson Duraes ◽  
J. Daniel Gezelter

We present a model to explain the mechanism behind enantiomeric separation under either shear flow or local rotational motion in a fluid. Local vorticity of the fluid imparts molecular rotation that couples to translational motion, sending enantiomers in opposite directions. Translation-rotation coupling of enantiomers is explored using the molecular hydrodynamic resistance tensor, and a molecular equivalent of the pitch of a screw is introduced to describe the degree of translation-rotation coupling. Molecular pitch is a structural feature of the molecules and can be easily computed, allowing rapid estimation of the pitch of 85 drug-like molecules. Simulations of model enantiomers in a range of fluids such as $\Lambda$- and $\Delta$-Ru(bpy)_3]Cl_2 in water and (R,R)- and (S,S)-atorvastatin in methanol support predictions made using molecular pitch values.A competition model and continuum drift diffusion equations are developed to predict separation of realistic racemic mixtures. We find that enantiomeric separation on a centimeter length scale can be achieved in hours, using experimentally-achievable vorticities. Additionally, we find that certain achiral objects can also exhibit a non-zero molecular pitch.


2021 ◽  
pp. 59-62
Author(s):  
U.A. Hasanova ◽  
◽  
Z.O. Qahramanova ◽  
P.F. Huseynova ◽  
◽  
...  

The synthesized S-enantiomer of the crown ether was used as an adsorbent to separate the racemic mixture of L-alanine ether of phenamine into individual diastereomers by column chromatography. Chromatographic separation occurred due to the formation of complexes of different stability between diastereomers and optically selective adsorbents on a host-guest principle. The separated diastereomers were converted into enantiomers by hydrolysis. The structure and optical activity of the synthesized crown ether and separated enantiomers were investigated by physicochemical methods


Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5350
Author(s):  
Laura García-Cansino ◽  
María Ángeles García ◽  
María Luisa Marina

The different activity and toxicity that the enantiomers of agrochemicals may have requires the development of stereoselective analytical methodologies enabling the individual determination of each enantiomer. The aim of this work was to develop the first Electrokinetic Chromatography methodology enabling the simultaneous enantiomeric separation of carfentrazone-ethyl herbicide and its hydrolysis metabolite carfentrazone. The use of an anionic cyclodextrin as chiral selector (captisol at 2.5% (w/v)) in a 25 mM acetate buffer, at a temperature of 30 °C, and an applied voltage (reverse polarity) of −30 kV, allowed the simultaneous separation of the four enantiomers of the two compounds studied in 6.8 min with enantiomeric resolutions of 5.0 for carfentrazone-ethyl and 5.1 for carfentrazone. Analytical characteristics of the developed method were evaluated and found adequate to achieve the quantitation of carfentrazone-ethyl and carfentrazone. Analysis of a commercial herbicide formulation showed the potential of the method for the quality control of these agrochemical products. Degradation studies for carfentrazone-ethyl revealed that no significant degradation took place in cleaned sand samples while a significant but not stereoselective degradation took place in soils for the whole period of time considered (seven days).


Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5241
Author(s):  
Mufarreh Asmari ◽  
Xiaoyu Wang ◽  
Natalia Casado ◽  
Marjan Piponski ◽  
Sergiy Kovalenko ◽  
...  

This review draws attention to the use of chiral monolithic silica HPLC columns for the enantiomeric separation and determination of chiral compounds. Properties and advantages of monolithic silica HPLC columns are also highlighted in comparison to conventional particle-packed, fused-core, and sub-2-µm HPLC columns. Nano-LC capillary monolithic silica columns as well as polymeric-based and hybrid-based monolithic columns are also demonstrated to show good enantioresolution abilities. Methods for introducing the chiral selector into the monolithic silica column in the form of mobile phase additive, by encapsulation and surface coating, or by covalent functionalization are described. The application of molecular modeling methods to elucidate the selector–selectand interaction is discussed. An application for enantiomeric impurity determination is also considered.


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