Formation, Characterization, and Occurrence of β-Carboline Alkaloids Derived from α-Dicarbonyl Compounds and l-Tryptophan

Abstract

β-Carbolines (βCs) 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 βcarbolines. Glyoxal afforded 1-hydroxymethyl-β-carboline (HME-βC) and its 3-carboxylic acid, and methylglyoxal afforded 1-(1hydroxyethyl)-β-carboline (HET-βC) and its 3-carboxylic acid. 2), and 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline (3). The formation of these βCs 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-βC-3-COOH intermediates, which were isolated and gave the βCs. These α-dicarbonyl-derived βCs 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-βC 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-βC was only detected in some foods with lower amounts than HET-βC. HET-βC appeared in foods as a racemic mixture of enantiomers suggesting the same mechanism of formation as the synthetized product. α-Dicarbonyl-derived βCs (HET-βC, HME-βC, and 1a/b-3) occur in foods and food processing and, therefore, they are ingested during diet.

Identification, Formation, and Occurrence of Perlolyrine: A β-Carboline Alkaloid with a Furan Moiety in Foods

“…In contrast, l -tryptophan did react with the α-dicarbonyl compound 3-DG and gave the βC perlolyrine (Figure ). The formation of perlolyrine from 3-DG occurred simultaneously to the formation of the carbohydrate-derived βCs, which also originated from this precursor: , 1-(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers ( 1a/b) , 1-(1,4,5-trihydroxypent-1-yl)-β-carboline ( 2 ), and 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline ( 3 ) (Figure ). The formation of perlolyrine from 3-DG and tryptophan was studied under different conditions of pH and temperature.…”

“…The formation of perlolyrine from tryptophan and 3-DG could follow the mechanism proposed in Figure . Initially, it follows the steps described before for carbohydrate-derived βCs and α-dicarbonyl-derived βCs. , Tryptophan reacts with 3-DG, affording through enolization, tautomerism, and cyclization the 3,4-dihydro-β-carboline-3-carboxylic acid intermediates with C 1′ -OH in the carbohydrate moiety. These intermediates were detected in the reactions of tryptophan with 3-DG or preheated fructose, at 70 °C and short times (4 h) by HPLC-MS ([M + H] + at m / z 349 and mass fragments at m / z 331 and 285), and absorbance spectra with a λ max at 355–375 nm.…”

“…Identification of perlolyrine in the samples was accomplished by HPLC with DAD and fluorescence spectra recording of the chromatographic peaks and coelution with authentic standards and confirmed by HPLC-MS. For identification purposes, SPE extracts were concentrated using a speed vacuum concentrator and analyzed by HPLC-MS (electrospray ionization mode, ESI + ), as previously reported. 28 The instrument used was a HPLC-MS Waters separations module Alliance e2695 with a quadrupole QDa Acquity and a Waters Photodiode Array Detector (PDA) 2996, working under positive electrospray ionization (ESI + ), and equipped with a 2.1 × 100 mm, 3 μm, 100 Å, C18 Atlantis T3 column (Waters). Chromatographic separation was accomplished with a program containing the eluents A (water), B (ACN), and C (2% formic acid) under a gradient going from 5% B, 5% C, and 90% A to 90% B, 5% C, and 5% A in 18 min.…”

“…Structures of tetrahydro-β-carbolines and aromatic βCs derived from carbohydrates ,, and the βC perlolyrine containing a furan moiety.…”

β-Carboline Alkaloids in Soy Sauce and Inhibition of Monoamine Oxidase (MAO)

“…β-Carbolines can be absorbed and accumulated in tissues contributing to their presence and actions in the biological systems [ 40 , 41 , 42 ]. These alkaloids have been found in foods and seasonings [ 22 , 24 , 43 , 44 , 45 , 46 , 47 , 48 ]. In this regard, soy sauce is a special seasoning made from salt, water, soybeans and wheat that, after heating processes, is traditionally fermented in a process involving molds, lactic bacteria and yeast lasting months, and this process may result in an increase of β-carboline alkaloids [ 49 ].…”