Enantioselective Fluorescent Sensors for Chiral Carboxylates Based on Calix[4]arenes Bearing an L‐Tryptophan Unit

Two-armed chiral calix[4]arenes (3a–c) functionalized at the lower ring with L-tryptophan units have been prepared and the structures of these receptors characterized by IR, MS, 1H, and 13C NMR spectroscopy and elemental analysis. The enantioselective recognition of these receptors has been studied by fluorescence titration and 1H NMR spectroscopy. The receptors exhibited different chiral recognition abilities towards some enantiomers of chiral materials and formed 1:1 complexes between host and guest. Receptor 3a exhibits excellent enantioselective fluorescent recognition ability towards the N-Boc-protected alanine anion and 3b reveals good enantioselective recognition ability towards the enantiomers of mandelate.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)