Utilization of (18-crown-6)-2,3,11,12-tetracarboxylic acid as a chiral NMR solvating agent for diamines and β-amino acids.
The compound (18-crown-6)-2,3,11,12-tetracarboxylic acid was evaluated as a chiral nuclear magnetic resonance (NMR) solvating agent for a series of diamines and bicyclic β-amino acids. The amine must be protonated for strong association with the crown ether. An advantage of (18-crown-6)-2,3,11,12-tetracarboxylic acid over many other crown ethers is that it undergoes a neutralization reaction with neutral amines to form the protonated species needed for binding. Twelve primary diamines in neutral and protonated forms were evaluated. Diamines with aryl and aliphatic groups were examined. Some are atropisomers with equivalent amine groups. Others have two nonequivalent amine groups. Association equilibria for these systems are complex, given the potential formation of 2:1, 1:1, and 1:2 crown-amine complexes and given the various charged species in solution for mixtures of the crown ether with the neutral amine. The crown ether produced enantiomeric differentiation in the (1) H NMR spectrum of one or more resonances for every diamine substrate. Also, a series of five bicyclic β-amino acids were examined and (18-crown-6)-2,3,11,12-tetracarboxylic acid caused enantiomeric differentiation in the (1) H NMR spectrum of three or more resonances of each compound.
Department of Chemistry, Bates College, Lewiston, Maine, USA.
Yolanda C
YC
Rodriguez
Department of Chemistry, Bates College, Lewiston, Maine, USA.
Tayla M
TM
Duarte
Department of Pharmaceutical Chemistry, University of Szeged, Szeged, Hungary.
Zsolt
Z
Szakonyi
Department of Pharmaceutical Chemistry, University of Szeged, Szeged, Hungary.
Enikő
E
Forró
Department of Pharmaceutical Chemistry, University of Szeged, Szeged, Hungary.
Ferenc
F
Fülöp
Department of Chemistry, Bates College, Lewiston, Maine, USA.
Thomas J
TJ
Wenzel
D000596:Amino Acids / Q000032:analysis / Q000737:chemistry*; D043844:Crown Ethers / Q000737:chemistry*; D003959:Diamines / Q000032:analysis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D012995:Solubility; D012997:Solvents / Q000737:chemistry*; D013237:Stereoisomerism
D000596:Amino Acids; D043844:Crown Ethers; D003959:Diamines; D012997:Solvents; C090732:18-crown-6 2,3,11,12-tetracarboxylic acid
NMR solvating agent; bicyclic β-amino acids; diamines