A Rapid and Sensitive Method for Chiroptical Sensing of a-Amino Acids via Click-like Labeling with o-Phthaladehyde and p-Toluenethiol

A highly practical method for comprehensive chiroptical sensing of free a amino acids with streamlined operation and high sensitivity via dual CD/UV measurements is developed. The assay takes advantage of an efficient and selective three-component labeling reaction of primary amines with o-phthalaldehyde and p-toluenethiol reagents, to derivatize the NH₂ group of analytes into an isoindole chromophore. The covalent labeling generates sensitive UV and CD readouts, both of which show excellent linear relationship with the concentration of analyte. The high reactivity and the novel chromogenic reporting mechanism allow fast and accurate measurement without background interference. The sensing assay works well for a remarkably broad range of analyte concentrations, with an unprecedented lower limit at 10 micromolar. We expect this method can be readily adapted for high throughput experimentation analysis using CD instrument equipped with a multiwell plate reader.