Ratiometric detection of cysteine by a ferrocenyl Michael acceptor

An activated ferrocenyl enone (1) by an intramolecular hydrogen bond was utilized as a Michael acceptor type of chemodosimeter for cysteine. The probe has shown selective response toward cysteine over other natural amino acids through the Michael addition reaction of a cysteinyl thiol group to 1. When cysteine was added, the prominent color change of 1 was observed so that submillimolar concentrations of cysteine were detectable by the naked eye.