Preparation and evaluation of the chiral stationary phases based on N-4-(2,5,6-trichloro-1,3-dicyano)-phenyl derivatives of L-α-amino acids

Regioselective functionalization of 2,4,5,6-tetrachloro-1,3-dicyanobenzene (TCDCB) by nucleophilic substitution of the chlorine atom at C(4) for N-L-alpha-amino acid residue enables preparation of new chiral selectors (1-5). Their binding to aminopropyl silica gel afforded new brush-type chiral stationary phases (CSP-1-CSP-4). Chiral stationary phases CSP-5 and CSP-6 that comprise dipeptide units L-Ala-L-Pro and L-Ala-L-Ala, respectively, were obtained by the solid-state coupling of C(4) substituted derivatives of 2,5,6-trichloro-1,3-dicyanobenzenes 4 and 5 to gamma-L-alanylaminopropyl silica gel. Best resolution for some of 23 test racemates was achieved with CSP-4 and CSP-6. This study reveals hydrogen bonding via a sterically exposed amide group and a pi-pi type interaction via an pi-acid persubstituted benzene ring in these CSPs as the main contribution to chiral recognition.