Enantiomer resolution of D- and L-alpha-amino acid derivatives by supercritical fluid chromatography on novel chiral diamide phases with carbon dioxide.

The rapid resolution of racemic N-4-nitrobenzoylamino acid isopropyl esters was accomplished without the loss of enantioselectivity by supercritical fluid chromatography (SFC) on novel chiral valine-diamide phases with carbon dioxide and a polar methanol modifier. In each stationary phase, a chiral moiety was anchored to the silica gel surface by a long decamethylene spacer. The enantioselectivity in SFC was comparable to that in liquid chromatography using 2-propanol-n-hexane. The time required for analysis was less than 5 min, and the range of enantiomer resolution (Rs) was 10.8-1.25. On using 2-propanol in place of methanol the separation was improved, but was accompanied by a decrease in column efficiency. The end-capping effect of the remaining surface silanols on enantiomer resolution is discussed.