RESUMO
ß-Carbolines (ßCs) are naturally occurring bioactive alkaloids, whereas α-dicarbonyl compounds are reactive substances generated in foods and in vivo. In this work, l-tryptophan reacted with α-dicarbonyl compounds affording new ß-carbolines. Glyoxal afforded 1-hydroxymethyl-ß-carboline (HME-ßC) and its 3-carboxylic acid, and methylglyoxal afforded 1-(1-hydroxyethyl)-ß-carboline (HET-ßC) and its 3-carboxylic acid. 3-Deoxyglucosone afforded 1-(1,3,4,5-tetrahydroxypent-1-yl)-ß-carboline isomers (1a/b), 1-(1,4,5-trihydroxypent-1-yl)-ß-carboline (2), and 1-(1,5-dihydroxypent-3-en-1-yl)-ß-carboline (3). The formation of these ßCs increased under acidic conditions and with increasing temperature. A mechanism is proposed explaining the conversion of a carbonyl into a hydroxy group based on tautomerism and cyclization to the dihydro-ßC-3-COOH intermediates, which were isolated and gave the ßCs. These α-dicarbonyl-derived ßCs occurred in model reactions of l-tryptophan with fructose or glucose incubated under heating and can be considered as advanced glycation end products (AGEs). They were also present in foods and formed during heating processes. HET-ßC appeared in processed foods, reaching up to 309 ng/g, with the highest amount found in dried tomato, fried onion, toasted bread, and Manuka honey. HME-ßC was only detected in some foods with lower amounts than HET-ßC. HET-ßC appeared in foods as a racemic mixture of enantiomers suggesting the same mechanism of formation as the synthetized product. α-Dicarbonyl-derived ßCs (HET-ßC, HME-ßC, and 1a/b-3) occur in foods and food processing and, therefore, they are ingested during diet.