Enantioselective recognition of aspartic acids by chiral ligand exchange potentiometry

Enantioselective resolution is realized by combining potentiometry with ligand exchange (CE) in a new method called chiral ligand exchange potentiometry (CLEP). A chiral selector, N-carbobenzoxy-L-aspartic acid (N-CBZ-L-Asp), preferentially recognizes D-aspartic acid (D-Asp) and undergoes ligand exchange with the enantiomeric labile coordination complexes of [Cu(II)(D-Asp)(2)] Or [Cu(II)(L-Asp)(2)] to form a diastereoisomeric complex [(D-Asp) Cu(II)(N-CBZ-L-Asp)] (a) or [(L-Asp)Cu(II)(N-CBZ-L-Asp)] (b). Considerable stereoselectivity occurs in the formation of these diastereoisomeric complexes, and their net charges were - 2 (a) and 0 (b), respectively, resulting in different Nernst factor (electrode slope), thus enabling chiral D-Asp to be distinguished by potentiometry without any pre- or postseparation processes.