25020-15-9

Non-enzymatic modification of l-tryptophan (1) and its metabolites and derivatives with aldehydes, via the Pictet-Spengler reaction, affords β-carbolines. Here we demonstrate that methylglyoxal (2) generates 1-acetyl-β-carbolines from tryptophan (1), from its methyl ester (6) and from tryptamine (4); however, 2 did not generate 1-(1-hydroxyethyl)-β-carboline derivates. HPLC analysis of model reaction systems showed formation of 1-acetyl-β-carboline (3) and 1-acetyl-β-carboline-3-carboxylic acid (5) during incubation of 1 and 2, at pH 5.7 and 7.4, at 100 °C, and only 5 at 37 °C, at the same pH values, with limited access of oxygen. Aerobic conditions caused higher formation of 3 at 37 °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-β-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-β-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-β-carboline-3-carboxylic acid (5) in some commercially available ketchups and in previously heated tomato concentrate.

Amadori compounds act as precursors in the formation of advanced glycation end products (AGEs) by non-enzymatic protein glycation, which are involved in ensuing protein damage. Pyridoxamine is a potent drug against protein glycation, and can act on several pathways in the glycation process. Nevertheless, the pyridoxamine inhibition action on Amadori compounds oxidation is still unclear. In this work, we have studied the Schiff base formation between pyridoxamine and various Amadori models at pH 7.4 at 37 °C in the presence of NaCNBH3. We detected an adduct formation, which suggests that pyridoxamine reacts with the carbonyl group in Amadori compounds. The significance of this mechanism is tested by comparison of the obtained kinetics rate constants with that obtained for 4-(aminomethyl)-pyridine, a structural analogue of pyridoxamine without post-Amadori action. We also study the chelating effect of pyridoxamine on metal ions. We have determined the complexation equilibrium constants between pyridoxamine, N-(1-deoxy-d-fructos-1-yl)-l-tryptophan, aminoguanidine, and ascorbic acid in the presence of Zn2+. The results show that the strong stability of pyridoxamine complexes is the key in its post-Amadori inhibition action. On the other hand results explain the lack of inhibition of aminoguanidine (a glycation inhibitor) in the post-Amadori reactions.

The reaction of L-tryptophan (Trp) with D-glucose under conditions that can occur during food processing and preparation was studied by high- performance liquid chromatography with diode array detection (HPLC/DAD). Besides the well-established glucose-tryptophan Amadori product (AP), (1R,3S)-1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-1,2,3,4-tetrahydro-β- carboline-3-carboxylic acid (PHP-THβC) was identified as an important product of this reaction. For preparation, PHPTHβC was obtained in high yields when Trp and D-glucose were reacted under strongly acidic conditions after heating in methanol. At elevated reaction temperatures (150 °C) 1- acetyl-β-carboline (acetyl-βC), was detected in significant concentrations. The mixtures were heated under variations of reaction time and temperature, and AP, PHP-THβC, and acetyl-βC were quantified. In the presence of air oxygen or mild, food relevant oxidants, such as L-dehydroascorbic acid, PHP- THβC was readily oxidized to a product that was identified as the previously unknown 1-(D-gluco-1,2,3,4,5-pentahydroxypentyl)-β-carboline (PHP-βC). Formation of PHP-THβC and PHP-βC in foodstuffs would deserve particular interest because multiple physiological activity of THβC and βC derivatives has been shown previously.

High resolution, 1H- (360 and 400 MHz) and 13C-n.m.r. (90.52 and 100.57 MHz) spectra of the mutarotated N-(1-deoxy-D-fructos-1-yl)-L-amino acids ("fructose-amino acids") 1-14 in D2O are reported.The 1H spectra allow unambiguous assignment of the signals o