Abstract
β-Carbolines are naturally occurring bioactive alkaloids. In this work, carbohydrate-derived β-carbolines (βCs), 1-(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers (1a/b), 1-(1,4,5-trihydroxypent-1-yl)-β-carboline (2), 1-(1,5-dihydroxypent-3-en-1-yl)-β-carboline (3), and 1-(1,2,3,4,5-pentahydroxypent-1-yl)-β-carboline (4) were identified and analyzed in commercial foods. The concentrations of βCs 1–4 in foods ranged from undetectable to 11.4 μg/g levels, suggesting their intake in the diet. Processed foods contained higher amounts than fresh or unprocessed foods, and the highest content was found in processed tomato and fruit products, sauces, and baked foods. βCs 1–3 were formed in foods during heating, and 1a/b were the main compounds. The formation of carbohydrate-derived βCs was studied in model reactions of tryptophan and carbohydrates. They formed in reactions of tryptophan with glucose under acidic conditions at temperatures higher than 80 °C. The formation of 1a/b was favored, but 2–3 increased at high temperatures. Noticeably, the βCs 1–3 formed in the reactions of tryptophan with fructose or sucrose, and the formation from fructose was much higher than from glucose. Thus, fructose was the main carbohydrate involved in the formation of 1–3, whereas sucrose gave these βCs after acid hydrolysis. It is shown for the first time that the mechanism of formation of βCs 1–3 occurs from the sugar intermediate 3-deoxyglucosone that reacts with tryptophan affording these carbohydrate-derived βCs. A mechanism of reaction to give βCs 1–3 is proposed that relies on the tautomerism (keto–enediol or enamine–imine) of intermediates involved in the reaction. Carbohydrate βCs 1–4 were assessed as inhibitors of monoamine oxidase (MAO), as antioxidants, and for their interaction with DNA. They were not good inhibitors of MAO-A or -B, were poor antioxidants, and did not appreciably interact with DNA.
Highlights
ABSTRACT: β-Carbolines are naturally occurring bioactive alkaloids
The compounds appeared in model reactions of tryptophan and glucose and in the reactions of tryptophan and fructose (Figure 2)
The mass spectra afforded the protonated molecular ion [M + H]+ and a fragmentation pattern dominated by successive loss of water (m/z 18) and fragmentation losses of C3H6O3 in 1, C2H4O2 in 2, and CH2O and C4H8O in 3.17 The compounds have different C-1′ configurations that were separated by high-performance liquid chromatography (HPLC) in the case of 1a/ b diastereoisomers
Summary
ABSTRACT: β-Carbolines are naturally occurring bioactive alkaloids. In this work, carbohydrate-derived β-carbolines (βCs), 1(1,3,4,5-tetrahydroxypent-1-yl)-β-carboline isomers (1a/b), 1-(1,4,5-trihydroxypent-1-yl)-β-carboline (2), 1-(1,5-dihydroxypent-3en-1-yl)-β-carboline (3), and 1-(1,2,3,4,5-pentahydroxypent-1-yl)-β-carboline (4) were identified and analyzed in commercial foods. Carboxylic acids (THβC-3-COOHs) arise from a reaction between L-tryptophan and aldehydes These reactions occur in foods, and a number of THβCs including carbohydrate-derived THβCs have been identified and quantified in foods.[1,12] Aromatic βCs arise from the oxidation of THβCs.[13] Among them, the βCs norharman and harman are two main compounds that occur in foods and which are generated in meats and fish during cooking.[13,14] These βCs arise from the corresponding THβC-3-COOHs that are the most abundant THβCs in foods.[15] In addition, other aromatic βCs such as those derived from carbohydrates may appear in foods (Figure 1).[1,16−19] glucose-derived aromatic βCs have been found in a number of foods and human urine.[1,17,20,21] Some of these βCs have been recently found in fruits of Nitraria tangutorum.[22] a few reports exist so far on the occurrence and activity of these compounds, whereas their mechanism of formation remains unknown. Journal of Agricultural and Food Chemistry pubs.acs.org/JAFC phan with carbohydrates.[12,23,24] It has been proposed that the carbohydrate-derived aromatic βCs might arise from the corresponding pentahydroxypentyl-THβC-3-COOH (PHPTHβC-3-COOH) formed from glucose and tryptophan (Figure 1).[1,12,16,23] the compound PHP-THβC-3-
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