Effect of the structure of organic phosphonate compounds on chiral separations on derivatized cellulose chiral stationary phase

Influence of steric hindrance on enantioseparation of Dns-amino acids and pesticides on terguride based chiral selectors in capillary electrophoresis

Three urea derivatives of ergoline-based chiral selectors (CSs), differing in the size of the urea side chain, i.e. dimethyl- (CSI), diethyl- (CSII), and diisopropylurea (CSIII), were used to study the effect of steric hindrance on the enantioseparation of dansyl amino acids (Dns-AAs), pesticides, and mandelic acid under condition of capillary electrophoresis (CE) in linear polyacrylamide coated capillaries. A mixture of organic modifiers (MeOH/THF, 4:1 v/v) in a BGE consisting of 100 mM beta-alanine-acetate was used to increase the solubility of CSs up to 25 mM. The capillary was filled with CS (high UV absorption), and the inlet and outlet vials contained buffer solutions only. The best enantioseparation of Dns-AAs was achieved on CSI. Increased steric hindrance of the chiral binding site led to reduction of both enantioselectivity and resolution. The opposite pattern was observed for the separation of mandelic acid enantiomers, where the best enantioseparation and resolution was obtained with CSIII. Most of the pesticides studied reached maximum selectivity on the diethylurea ergoline derivative (CSII). Enantioseparation of fenoxaprop was found to be independent of steric hindrance.

Chiral separation of organic phosphonate compounds on cellulose CSP (chiral stationary phase) under reversed phase mode

The enantiomers of fourteen O,O-dialkyl-2-benzyloxycarbonyl-aminoarylmethyl-phosphonates are directly separated on the tris(3,5-dimethylphenylcarbamate) cellulose column (Chiralcel OD-R) under reversed phase mode. The results of the chiral separation are different from the results obtained in the normal phase mode. The mobile phase plays an essential role in chiral discrimination when using Chiralcel OD-R. The influences of the mobile phase composition on the retention and the enantioselectivity are investigated. The influences on chiral separation of the length and steric hindrance of alkoxy groups of the phosphonate ester and of the nature of the substituent on the benzene ring that is attached to the chiral carbon atom are also discussed.