L-Amino acid derived pyridinium-based chiral compounds and their efficacy in chiral recognition of lactate

A series of pyridinium-based chiral compounds 1–6 have been designed and synthesized. L-Amino acids have been used as the chiral source in the molecules. Among the chiral compounds, an L-valine derived compound 1 was found to exhibit enantioselective recognition of D-lactate in fluorescence. Structural tuning of this derivative, either by replacing L-valine with L-alanine or L-phenylglycine or by reducing the number of chiral centres around the binding site, does not result in any significant change in enantioselectivity in the recognition process. Change of the urea site to amide introduces compound 6 that displays good enantiodiscrimination for lactate (enantiomeric fluorescence difference ratio ef = 28.33 for D-lactate), even better than that of the L-valine derived compound 1 and of other reported structures in the literature.