Comparative Enantioseparation of 2‐Arylpropionic Acid Esters on Cellulose Derivative and (S,S)‐Whelk‐O 1 Columns

Abstract

Cellulose‐derivative chiral stationary phases (CSPs) have been proven to be the most useful CSPs because of their versatility and capability. However, the exact chiral recognition mechanism on these CSPs is still unclear due to the complexity of these CSPs. In the present study, we attempt to compare the difference of the chiral recognition mechanism between cellulose‐derivative CSPs and (S,S)‐Whelk‐O 1 using ketoprofen esters, tropic acid esters, and racemic naproxen esters. The results revealed that alkoxy groups have great influence on the chiral recognition of 2‐arylpropionic acid esters on cellulose‐derivative CSPs or (S,S)‐Whelk‐O 1. From methyl ester to sec‐butyl ester, the chiral selectivity (α) is systematically changed on (S,S)‐Whelk‐O 1, whereas it does not follow any particular trend on cellulose‐derivative CSPs, suggesting that the attractive interactions between CSP and solute were the predominant factor for the chiral recognition on (S,S)‐Whelk‐O 1, although the inclusion and steric fitness of solutes into the chiral cavities might be the dominant chiral recognition mechanism for cellulose‐derivative CSPs. With several exceptions, there exists some kind of correlation between the ester kind and a different kind of cellulose‐derivative CSP. The influence of mobile phase modifier on the enantioseparation of 2‐arylpropionic acid esters on the cellulose‐derivative chiral columns was also extensively studied. Four types of influence resulting from using different alcoholic modifier in mobile phase were observed. The influence of alcoholic modifier on the enantioseparation was mainly through the alteration of steric environment of chiral cavities and this influence is solute dependent. Furthermore, the results suggested that the hydrogen‐bonding interaction between solute and CSP might not be important for the chiral recognition of ketoprofen esters, tropic acid esters, or racemic naproxen esters on cellulose tris(3,5‐dimethylphenylcarbamate) (CDMPC).

Keywords:

• Chiral stationary phase
• Chiral recognition mechanism
• Cellulose derivative
• Mobile phase modifier
• 2‐Arylpropionic acid ester

Acknowledgment

We are grateful to Prof. Dr. Kinkel in Georg‐Simon‐Ohm University of Applied Science (Nürnberg, Germany) for providing the (S,S)‐Whelk‐O 1 chiral column, one kind of silica gel, and four kinds of standard chiral compounds [Tröger's base, trans‐stilbene oxide, benzoin, and 2,2,2‐trifluro‐1‐(9‐anthryl)‐ethanol].