ARCA forms an imine with amino acids at basic condition. Hydrogen bonding between N of imine and OH, along with hydrogen bonding between the urea proton and the carboxylic anion take place. Depending on the optical properties of α-amino acids, the steric hindrance between Alkyl position of α-proton and H of imine may occur which affects the stability.
S-ARCA, as seen in the picture below, exhibits a higher stability with D-amino acids due to less steric hindrance. The NMR pattern shows that the stronger hydrogen bond between the urea proton group and the carboxyl group may contribute to greater receptor stereoselectivity for binding D-amino acids.
Applying this mechanism, ARCA can be an effective extractant for the resolution of racemic amino acids, and can convert amino acids from an L- to D-form or from a D- to L-form at organic basic condition.