Features of the adsorption of Naproxen on the chiral stationary phase (S,S)-Whelk-O1 under reversed-phase conditions

A comprehensive study to reveal the potential of a more sustainable ultra-high performance enantioselective reversed-phase chromatography on Pirkle-type stationary phase, with Whelk-O1 as a case study

In this study, we aimed to make enantioselective chromatography more sustainable, more sensitive, and compatible with aqueous formulations analysis and ESI-MS. To achieve this, we examined the effects of transitioning from normal-phase chromatography (which uses hydrocarbon-based solvents) to reversed-phase chromatography (using mobile phases based on water) using broad-spectrum Whelk-O1 columns as a critical study. For the first time, we holistically compared the thermodynamics and kinetics of the two elution modes in order to answer the question of whether same-column chemistry can effectively separate the compounds even in reversed-phase mode and found, unexpectedly, that reversed-phase chromatography using acetonitrile as the organic modifier was competitive from a kinetic standpoint. We also evaluated the effectiveness of three organic modifiers simultaneously on a sample of 11 molecules already resolved in NP conditions with different resolutions and achieved a resolution value of 1.5 for 91% and a resolution value of 2 for 82% of cases. Finally, we separated three racemates (within a k factor of 9) using only 480 µL of solvent per chromatographic run on a millibore column of 1 mm I.D., demonstrating that our approach allows for greener chromatographic separations.

Resolution, determination of enantiomeric purity and chiral recognition mechanism of new xanthone derivatives on (S,S)-whelk-O1 stationary phase

The enantioresolution and determination of the enantiomeric purity of 32 new xanthone derivatives, synthesized in enantiomerically pure form, were investigated on (S,S)-Whelk-O1 chiral stationary phase (CSP). Enantioselectivity and resolution (α and R_S ) with values ranging from 1.41-6.25 and from 1.29-17.20, respectively, were achieved. The elution was in polar organic mode with acetonitrile/methanol (50:50 v/v) as mobile phase and, generally, the (R)-enantiomer was the first to elute. The enantiomeric excess (ee) for all synthesized xanthone derivatives was higher than 99%. All the enantiomeric pairs were enantioseparated, even those without an aromatic moiety linked to the stereogenic center. Computational studies for molecular docking were carried out to perform a qualitative analysis of the enantioresolution and to explore the chiral recognition mechanisms. The in silico results were consistent with the chromatographic parameters and elution orders. The interactions between the CSP and the xanthone derivatives involved in the chromatographic enantioseparation were elucidated.

Enantioresolution of chiral derivatives of xanthones on (S,S)-Whelk-O1 and L-phenylglycine stationary phases and chiral recognition mechanism by docking approach for (S,S)-Whelk-O1

The resolution of seven enantiomeric pairs of chiral derivatives of xanthones (CDXs) on (S,S)-Whelk-O1 and L-phenylglycine chiral stationary phases (CSPs) was systematically investigated using multimodal elution conditions (normal-phase, polar-organic, and reversed-phase). The (S,S)-Whelk-O1 CSP, under polar-organic conditions, demonstrated a very good power of resolution for the CDXs possessing an aromatic moiety linked to the stereogenic center with separation factor and resolution factor ranging from 1.91 to 7.55 and from 6.71 to 24.16, respectively. The chiral recognition mechanisms were also investigated for (S,S)-Whelk-O1 CSP by molecular docking technique. Data regarding the CSP-CDX molecular conformations and interactions were retrieved. These results were in accordance with the experimental chromatographic parameters regarding enantioselectivity and enantiomer elution order. The results of the present study fulfilled the initial objectives of enantioselective studies of CDXs and elucidation of intermolecular CSP-CDX interactions.