Chiral CE separation of dopamine-derived neurotoxins.

An enantiomeric separation of dopamine-derived neurotoxins by capillary electrophoresis has been developed. Tetrahydroisoquinoline (TIQ), dopamine (DA), (R/S)-1-benzyl-TIQ (BTIQ), (R/S)-6,7-dihydroxy-1-methyl-TIQ (salsolinol, Sal), and (R/S)-6,7-dihydroxy-1, 2-dimethyl-TIQ (N-methyl-salsolinol, NMSal) were studied as model compounds. The CE running buffer (50 mM phosphate buffer at pH 3.0) contained 1.5 M urea and 12 mM beta-CD as a chiral selector. During separation, the (R)-enantiomers formed more stable inclusion complexes with beta-CD, and thus had a longer migration time than their optical antipodes. It was noticed that the recovery rates of these TIQ derivatives were very poor (< 15%) during protein precipitation, a procedure widely used for cleaning up biological samples. The recovery was significantly improved by pre-mixing the sample with a surfactant (e.g., sodium hexanesulfonate or Triton X-100) to reduce the co-precipitation. The present method in combination with electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied to study samples obtained from in vitro incubation of two catecholamines, dopamine and epinine, with aldehydes forming neurotoxins including (S)- and (R)-NMSal enantiomers. The later is known to induce Parkinsonism in rats.