Sulfonation of 3,3'-Diformyl-BINOL for Enantioselective Fluorescent Recognition of Amino Acids in Water.

Reaction of (R)-3,3'-diformyl-1,1'-bi-2-naphthol with concentrated sulfuric acid gives the corresponding 6,6'-disulfonated compound (R)-2 selectively. This provides a simple and efficient method to convert a water-insoluble compound to a water-soluble fluorescent probe. It is found that (R)-2 in combination with Zn2+ shows a highly enantioselective fluorescent response toward various amino acids in the aqueous HEPES buffer solution at pH 7.4. For example, an enantioselective fluorescence enhancement ratio [ef=ΔID /ΔIL ] up to 35.8 is observed for the recognition of asparagine. NMR and mass spectroscopic investigations are conducted to explore the reaction of (R)-2 with asparagine.