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Utilization of (18‐Crown‐6)‐2,3,11,12‐tetracarboxylic Acid as a Chiral NMR Solvating Agent for Diamines and β‐Amino Acids
Author(s) -
Rodriguez Yolanda C.,
Duarte Tayla M.,
Szakonyi Zsolt,
Forró Enikő,
Fülöp Ferenc,
Wenzel Thomas J.
Publication year - 2015
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.22491
Subject(s) - chemistry , crown ether , protonation , diamine , amine gas treating , enantiomer , bicyclic molecule , ether , medicinal chemistry , 18 crown 6 , stereochemistry , organic chemistry , molecule , ion
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. Chirality 27:708–715, 2015 . © 2015 Wiley Periodicals, Inc.