Applied Circular Dichroism: A Facile Spectroscopic Tool for Configurational Assignment and Determination of Enantiopurity

Abstract EN

In order to determine if electronic circular dichroism (ECD) is a good tool for the qualitative evaluation of absolute configuration and enantiopurity in the absence of chiral high performance liquid chromatography (HPLC), ECD studies were performed on several prescriptions and over-the-counter drugs.

Cotton effects (CE) were observed for both S and R isomers between 200 and 300 nm.

For the drugs examined in this study, the S isomers showed a negative CE, while the R isomers displayed a positive CE.

The ECD spectra of both enantiomers were nearly mirror images, with the amplitude proportional to the enantiopurity.

Plotting the differential extinction coefficient ( Δ ε ) versus enantiopurity at the wavelength of maximum amplitude yielded linear standard curves with coefficients of determination ( R 2 ) greater than 97% for both isomers in all cases.

As expected, Equate, Advil, and Motrin, each containing a racemic mixture of ibuprofen, yielded no chiroptical signal.

ECD spectra of Suphedrine and Sudafed revealed that each of them is rich in 1S,2S-pseudoephedrine, while the analysis of Equate vapor inhaler is rich in R-methamphetamine.