Enantioselective Fluorescent Recognition of Amino Acids by Amide Formation: An Unusual Concentration Effect

A BINOL-based perfluoroalkyl ketone shows a highly enantioselective fluorescence enhancement in the presence of various amino acid-TBA salts and can be used to determine the enantiomeric composition of these compounds. It was found that the amino acid-TBA salts can act as nucleophiles to cleave the perfluoroalkyl group off of the ketones to form the corresponding amides at room temperature in DMSO. This is the first example of an enantioselective fluorescent sensor for the recognition of amino acids by forming amide bonds under very mild conditions. This study has also revealed an unusual concentration effect leading to an "off-on-off" fluorescence response of the sensor toward one enantiomer of the amino acids.