Separation, Analysis And Preparation Of Enantiomers Of β-Amino Acids

The past decade has seen a growing interest inβ-amino acids, which are important intermediates for the synthesis of compounds of pharmacertical interest and are important constituents of natural products such as alkalaids, peptides andβ-lactam antibiotics. The incorporation of ofβ-amino acids has been successful in creating peptidomimetics that not only have potent biological activity, but are also resistant to proteolysis. Enantiomers ofβ-amino acid probably show different pharmacological behaviors and undergo different metabolic pathways in vivo. To study the pharmacological and metabolic properties of chiral drugs, the pure enantiomer must be obtained. In this thesis, we report the development of chiral separation methods using capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) and their applications in separation ofβ-amino acid enantiomers. The thesis work can be devided into three parts as follows:First, we developed a capillary electrophoretic method for separation of enantiomers ofβ-amino acids. In this method, chiral crown ether (-)-18-crown-6-tetracarboxylic acid (18C6H₄), was chosen as chiral resolving agent. The crown ether was synthesized in-house by following esterization, amidization, cyclonization, and hydrolyzation steps. The chiral separation is based on the fact that primary amines which are protonated at low pH values can be enclosed in the chiral cavity of the crown ether, thus forming transient complexes of different stability for a pair of enantiomers. All fiveβ-amino acid racemates were resolved into enantiomers by the chiral capillary electrophoresis developed in this work with separation factor up to 1.08. We further measured the binding constants between 18C6H4 andβ-amino acids according to mobility shift method. Preliminary results indicate that chiral separation method based on CE with chiral additive offers the merits of easy operation and fast separations ofβ-amino acids.Then, we developed two HPLC methods that allow the separation ofβ-amino acid enantiomers from their synthetic racemates. Firstly, chiral separation ofβ-amino acids was achieved in a reverse phase liquid chromatography (RPLC) using optically pure L-phenylalanine as a chiral mobile phase additive(CMPA). The chiral ligand in the mobile phase can form diastereomers with racemicβ-amino acids in the presence of metal ions such as Cu²⁺ and the diastereomers can be readily resolved on a RPLC system. However, the CMPA method suffers from a number of problems...