AUTHOR=Nakakoji Takashi , Yoshino Kaori , Izutsu Kazuki , Sato Hirofumi , Miyake Hiroyuki , Mieda Eiko , Shinoda Satoshi , Tsukube Hiroshi , Kawasaki Hideya , Arakawa Ryuichi , Ono Daisuke , Shizuma Motohiro 

TITLE=Enantioselectivity-Evaluation of Chiral Copper(II) Complexes Coordinated by Novel Chiral Tetradentate Ligands for Free Amino Acids by Mass Spectrometry Coupled With the Isotopically Labeled Enantiomer Method

JOURNAL=Frontiers in Chemistry

VOLUME=Volume 8 - 2020

YEAR=2020

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2020.598598

DOI=10.3389/fchem.2020.598598

ISSN=2296-2646

ABSTRACT=Chiral copper(II) complexes with chiral tetradentate ligands, which are N,N-ethylene-bridged bis(S-amino acid amide or ester) prepared from S-alanine, S-phenylalanine, S-valine or S-proline, generated in methanol. The copper complexes made three component complexes with free chiral amino acid as the second ligand enantioselectively. The enantioselectivity was evaluated by electrospray ionization-mass spectrometry coupled with the deuterium-labeled enantiomer method. These copper complexes showed high enantioselectivity for free amino acids having bulky side chains, suggesting that steric interaction is a major factor in chiral recognition. The copper complex with chiral ligand prepared from S-proline showed opposite enantioselectivity to copper complexes with ligands from other S-amino acids.  The conformational difference of the tetradentate ligand in the copper complex was found to be significant for enantioselectivity.