Design of Selenium-Based Chiral Chemical Probes for Simultaneous Enantio- and Chemosensing of Chiral Carboxylic Acids with Remote Stereogenic Centers by NMR Spectroscopy
Enantiomers of a few new amides containing two stereogenic centers have been derived from D- and L-α-amino acids as guests for chiral recognition by 1H NMR spectroscopy. A variety of...
Derivatization of compounds containing -OH groups can be accomplished quantitatively with 1,3,2-dioxaphospholanyl chloride. The chemical shifts of phosphorus in the derivatives clearly differentiate alcohols from phenols and carboxylic acids. Quantitation is obtained by use of 31P FT-NMR spectroscopy in the presence of 2,2,6,6-tetrameth-ylpiperidinyloxy free radical to shorten relaxation times. Compounds with phosphorus chemical shifts differing by as little as 0.1 ppm can be separately determined.
Nine new (+)-dehydroabietylimidazolium salts were synthesised and studied as chiral solvating agents for several different racemic aromatic and non-aromatic carboxylate salts. These cationic chiral solvating agents resolve racemic ionic analytes better than non-ionic ones. Bis(dehydroabietylimidazolium) bis(trifluoromethanesulfonimide) gave the best discrimination for the enantiomers of carboxylate salts. Its resolution behaviour was studied by an NMR titration experiment, which indicated 1 : 1 complexation with the racemic analyte. The dehydroabietylimidazolium salts were also useful in enantiomeric excess (ee) determinations, and for the recognition of chirality of racemic aromatic and non-aromatic α-substituted carboxylic acids.
Optically Pure Aziridin-2-yl Methanols as Readily Available 1H NMR Sensors for Enantiodiscrimination of α-Racemic Carboxylic Acids Containing Tertiary or Quaternary Stereogenic Centers