Ethyl 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylate: a novel β-carboline found in alcoholic beverages

A novel tetrahydro-β-carboline, chemically identified as 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid ethyl ester (ethyl 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylate) (MTCA-EE), has been found in alcoholic beverages ranging from an undetectable amount to 534 μg/l. RP-HPLC with fluorescence detection and GC–MS were used for characterization. MTCA-EE occurred as two diastereoisomers 1S,3S and 1R,3S with an average ratio (SS/RS) of 2.21. The concentration of MTCA-EE (1S,3S plus 1R,3S) was 109.6–534 μg/l in sherry wines, 75.2–140.7 μg/l in sparkling wines, 3.4–161.65 μg/l in red and white wines, 32.7–47.2 μg/l in port wines, and 8.7–37.2 μg/l in sake. MTCA-EE seemed to occur in some high alcohol beers at less than 10 μg/l. Most distilled alcoholic beverages did not contain MTCA-EE although, exceptionally, one brandy reached 28.6 μg/l. 1-Methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid (MTCA) and l-tryptophan ethyl ester (l-TRP-EE) were two precursors leading to MTCA-EE. Alcoholic drinks containing MTCA-EE and MTCA could be an exogenous source of bioactive β-carbolines found in vivo. MTCA-EE is a structural analogue (reduced pyrido ring) of β-carboline-3-carboxylic acid ethyl ester (β-CCE), a potent benzodiazepine receptor inverse agonist. ©