Title:
Occurrence and importance of technologically formed alkaloids in food: On-line HPLC tandem mass spectrometry (HPLC-MS/MS) for the analysis of bioactive tryptophan derivatives
Project management at the University of Würzburg:
Participating scientists:
Abstract:
First, the studies were focused on the structural-specific detection of tetrahydro-ß-carbolines (thc) and condensation products of tryptophan (trp)/tryptamine with aldohexoses. By means of synthesized reference compounds a series of novel thc carboxylic acids were identified in food in the range from < 50 micrograms/kg to > 10 mg/kg, i.e. among others 1,2,3,4-thc-1-carboxylic acid, 1-methyl-1,2,3,4-thc-1-carboxylic acid, 1-(2-carboxyethyl)-1,2,3,4-thc-1-carboxylic acid and 1-(2-carboxyethyl) thc. As nitrosation products of thc, 3,4-dihydro-ß-carbolines and harman alkaloids were identified for the first time.
In model reactions carried out with D-glucose, D-mannose and D-galactose novel trp-N-glycosides and glyco-thc derivatives were found which were also detected in food in a subsequent screening. In human urine, 2-(alpha-mannopyranosyl)-L-trp was characterized. In addition, thc and trp glycoconjugates were described for the first time as water-soluble ligands of the ah receptor.
The attention of subsequent studies was focused on (i) the enzymatic glycosylation of trp in fruits; (ii) the chemical glycosylation of trp with aldopentoses; and (iii) the non-enzymatic glycosylation of peptid-/protein-bound trp residues. (i) By means of the identification of N1-(ß-D-glucopyranosyl-4C1-)-L-trp and subsequent biogenesis studies, enzymatic trp-N-glycosylation was demonstrated. The compound was found in fruits and fruit juices in the range of 100 migrograms/l to 20 mg/l. (ii) In model reactions performed with D-ribose, D-xylose, and D-arabinose, a number of novel trp-C-glycosyl derivatives, trp-N-glycosides and glyco-thc-3-carboxylic acids were detected. Numerous ß-carboline derivatives were shown to be secondary products of the trp glycosylation. (iii) At the example of the nonapeptide trp-ala-gly-asp-ala-ser-gly-glu the contribution of the indol chain in the glycosylation of the peptide was demonstrated. A distinct neighboring group effect of aspartic acid in the course of the glycosylation of trp-containing peptides with asp-trp-x was shown. By the identification of trp-N-pentosides in the digestion of ribosylated lysozyme the contribution of the indol nitrogen within the glycosylation of protein-bound trp was demonstrated for the first time.
Key words:
Tryptophan glycoconjugates
Tryptophan-N-glucoside
Tetrahydro-ß-carbolines
ß-Carbolin-alkaloids
HPLC-MS/MS
Ah-Rezeptor
Projekt period: from 09.1995 to 03.2001
Funding institution:
DFG ,Granting date: 01.07.1995
Publications:
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Research area