Determination of dopamine and dopamine-derived ( R)-/( S)-salsolinol and norsalsolinol in various human brain areas using solid-phase extraction and gas chromatography/mass spectrometry

Abstract

Using a solid-phase extraction procedure and a gas chromatographic–mass spectrometric (GC/MS) method the levels of dopamine and the levels of dopamine-derived salsolinol (SAL) and norsalsolinol (NorSAL) were determined in human brain areas involved in the etiology of alcoholism, parkinsonism and other diseases. The possibility that biosynthesis of salsolinol occurs through a stereospecific enzymatic reaction was considered. Using a two-step derivatization with N-methyl- N-trimethylsilyltrifluoracetamide (MSTFA) and the chiral reagent ( R)-(−)-2-phenylbutyryl chloride, baseline separated peaks of ( R)- and ( S)-SAL were obtained. Both enantiomers were found in human brain samples with no correlations between levels of salsolinol and dopamine. These findings do not support the hypothesis that only an enantio-selective synthesis of ( R)-SAL by a putative salsolinol synthase is responsible for the in vivo formation. In our opinion, non-enzymatic formation of salsolinol via the Pictet–Spengler reaction reveals both salsolinol enantiomers and an additional enzymatic synthesis of only ( R)-SAL explains the enantiomer ratio ( R)-/( S)-SAL of approximately 2.