title: The role of methylglyoxal in the non-enzymatic conversion of tryptophan, its methyl ester and tryptamine to 1-acetyl-beta-carbolines.
abstract: Non-enzymatic modification of l-tryptophan (1) and its metabolites and derivatives with aldehydes, via the Pictet-Spengler reaction, affords beta-carbolines. Here we demonstrate that methylglyoxal (2) generates 1-acetyl-beta-carbolines from tryptophan (1), from its methyl ester (6) and from tryptamine (4); however, 2 did not generate 1-(1-hydroxyethyl)-beta-carboline derivates. HPLC analysis of model reaction systems showed formation of 1-acetyl-beta-carboline (3) and 1-acetyl-beta-carboline-3-carboxylic acid (5) during incubation of 1 and 2, at pH 5.7 and 7.4, at 100 degrees C, and only 5 at 37 degrees C, at the same pH values, with limited access of oxygen. Aerobic conditions caused higher formation of 3 at 37 degrees C at both pH values, while, at higher temperature, the same effect was only observed at pH 5.7. Lack of oxygen did not much influence the formation of 3 or 5 at both pH and temperature values, in comparison with the formation at limited access of oxygen. Incubation of 2 and 6 generated methyl-1-acetyl-beta-carboline-3-carboxylate (7) together with 3 and 5 as a result of hydrolysis of 6 into 1 and, partially, 7 into 5, while in incubation mixtures of 2 and 4 only unstable 1-acetyl-3,4-dihydro-beta-carboline (8) was observed. Incubation of 1 with d-glucose as well as incubation of tryptophan with Amadori product 18 under similar conditions did not generate carbolines 3 or 5. For the first time, we were able to demonstrate the presence of 1-acetyl-beta-carboline-3-carboxylic acid (5) in some commercially available ketchups and in previously heated tomato concentrate.
authors.affiliation: Division of Organic Chemistry and Biochemistry, Ruder Bosković Institute, Bijenicka cesta 54, PO Box 180, HR-10 002 Zagreb, Croatia.
authors.forename: Ina
authors.initials: I
authors.lastname: Nemet
authors.forename: Lidija
authors.initials: L
authors.lastname: Varga-Defterdarović
mesh_terms: D000107:Acetylation; D002243:Carbolines / Q000138:chemical synthesis* / Q000737:chemistry; D004798:Enzymes / Q000378:metabolism; D004952:Esters / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D018551:Solanum lycopersicum / Q000737:chemistry; D013058:Mass Spectrometry; D015394:Molecular Structure; D011765:Pyruvaldehyde / Q000737:chemistry*; D013696:Temperature; D014363:Tryptamines / Q000737:chemistry*; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D002243:Carbolines; D004798:Enzymes; D004952:Esters; D014363:Tryptamines; C030820:tryptamine; D011765:Pyruvaldehyde; D014364:Tryptophan