Kinetic recognition of L-DOPA and D-DOPA by using a clock system

Chiral enantiomers of drugs often exhibit distinct pharmacological activities despite their similar physical and chemical properties. Developing efficient methods for their distinguishment is crucial for pharmaceutical quality control. Here, we presented a novel approach using a CTT (Chlorite-Tetramethylammonium Hydroxide-Tetrathionate) clock reaction system for kinetic chiral enantiomer recognition. DOPA enantiomers were selected for this purpose, in which L-DOPA is therapeutic efficacy in treating Parkinson's disease by precursoring dopamine while D-DOPA lacks such a function. By introducing equal amounts of L-DOPA and D-DOPA into the CTT clock system, we observed a more prolonged induction period for L-DOPA compared to D-DOPA, enabling their quick differentiation. Moreover, a linear relationship between the induction period and the concentration (1.190 × 10 −6  mol/L to 4.5238 × 10 −6  mol/L) of L-DOPA or D-DOPA allowed quantitative detection of L-DOPA or D-DOPA samples. This method could also be applied to analyze varying concentration ratios of L-DOPA and D-DOPA mixtures at a fixed total concentration. Study on mechanism indicates that both L-DOPA and D-DOPA react with ClO 2 · radical to finally generate DHICA through oxidation, with their kinetic disparities evident during this process. These kinetic disparities between L-DOPA and D-DOPA oxidation arises from stereospecific hydrogen-bonding interactions in the cyclodopa intermediate. The weaker hydrogen bond in L-DOPA-derived cyclodopa likely facilitates its cleavage during oxidation, thereby accounting for the faster reaction kinetics observed in the clock system compared to D-DOPA. This makes L-DOPA exhibit more fast consumption of chlorine dioxide than D-DOPA, and resulting larger the extension in the induction period with L-DOPA than that with D-DOPA. Such a method coupling CCT clock demonstrates its versatility and potential for broader applications in chiral drug analysis.