Markus Herderich

Identification of quercetin glucuronides in human plasma by high-performance liquid chromatography–tandem mass spectrometry

After intake of food or herbal medicinal products containing quercetin glycosides, the systemic availability of the genuine glycoside, as well as the systemic occurrence of the aglycone or conjugates of this polyphenol has been a matter of dispute. Consequently, we designed this study to develop a reliable method for determination of quercetin and its metabolites. Following consumption of fried onions five different glucuronides of quercetin could be identified in human plasma samples by means of HPLC-UV-MS/MS. Selective determination of the target compounds was achieved by simultaneous UV (254 nm) and MS/MS detection with selected reaction monitoring experiments using positive mode electrospray ionisation. In contrast, neither the free flavonol nor the genuine glycoside could be detected in plasma. Identification of the quercetin glucuronides detected in vivo was confirmed by comparison with authentic reference compounds synthesised enzymatically using glucuronyl transferase from rabbit liver.

Analysis of phosphorylated carbohydrates by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry utilising a β-cyclodextrin bonded stationary phase

Abstract Chromatographic separation of phosphorylated carbohydrates was achieved on a β-cyclodextrin (CD) bonded HPLC column. Applying acetonitrile–aqueous ammonium acetate gradient elution, the separation of sugar phosphates relied on the combination of anion-exchange and hydrophilic interaction properties of CD bonded phases in the presence of ammonium ions. Furthermore, this solvent system allowed on-line coupling to electrospray ionization mass spectrometry (ESI-MS) and direct structural characterisation of carbohydrate phosphates by tandem mass spectrometry (MS–MS). In addition to the analysis of various pentose and hexose phosphates, the HPLC–ESI-MS–MS method was successfully applied to demonstrate the enzymatic formation of D-1-deoxyxylulose 5-phosphate from pyruvate and glyceraldehyde phosphate catalysed by yeast transketolase.

Escherichia coli produces phosphoantigens activating human gamma delta T cells.

Human Vγ9δ2 T lymphocytes are suggested to play an important role in the immune response to various microbial pathogens. In contrast to αβ T cells, γδ T lymphocytes recognize small, non-protein, phosphate-bearing antigens (phosphoantigens) in a major histocompatibility complex-independent manner. Four different phosphoantigens termed TUBag1 to TUBag4 with a common 3-formyl-1-butyl-pyrophosphate moiety and isopentenyl-pyrophosphate have been isolated and identified from mycobacteria. However, natural occurring γδ T cell ligands from other bacterial species were not characterized so far. Here, we describe the structural identification of the two compounds responsible for the γδ T cell-stimulating capacity of Escherichia coli as similar to the mycobacterial phosphoantigens 3-formyl-1-butyl-pyrophosphate and itsM r 275 homologue TUBag2. In addition,E. coli phosphoantigens exert bioactivities on γδ T cells with similar potencies to the mycobacterial phosphoantigens at 5–15 nm concentration. Furthermore, our results clearly prove that the deoxyxylulose 5-phophate pathway (also referred to as Rohmer metabolic route of isoprenoid biosynthesis) is essential for the biosynthesis of the phosphoantigens in E. coli. Because this pathway is absent from human cells, it proves an ideal target for focusing efficiently the antimicrobial selectivity of human γδ T lymphocytes.

Tryptophan‐derived bioactive compounds in food

Abstract This survey covers analysis, occurrence, and formation of tryptophanderived compounds in food and edible plants as well as dietary and metabolic aspects of tryptophan derivatives. After summarizing biosynthesis and metabolism of tryptophan, attention is focused on products obtained by oxidative degradation reactions, compounds derived from the Maillard reaction, tetrahydro‐s‐carbolines, and harman derivatives. In addition, formation of heterocyclic aromatic amines and relevance of tryptophan contaminants for the outbreak of the eosinophilia‐myalgia syndrome (EMS) are reviewed.

Acetogenic isoquinoline alkaloids. CXII. Separation and identification of dimeric naphthylisoquinoline alkaloids by liquid chromatography coupled to electrospray ionization mass spectrometry

The atropodiastereomeric dimeric naphthylisoquinoline alkaloids, michellamines A (1a), B (1b) and C (1c), together with their monomers, korupensamines A (2a) and B (2b), were investigated using electrospray ionization tandem mass spectrometry coupled to liquid chromatography (LC-ESI-MS-MS). From the spectra obtained, characteristic product ions were chosen to monitor the chromatographic separation achieved on an RP-18 column. Under acidic conditions required for chromatographic analysis, the monomeric alkaloids 2a and 2b yielded protonated molecules [M + H]+, while the dimers, the michellamines, exhibited doubly protonated [M + 2H]2+ molecules. In addition, the coeluting alkaloids 1b and 2b were identified unambiguously be means of tandem mass spectrometry. Thus, together with the retention times of the alkaloids, the product ion spectra allowed us the identification of michellamines in the presence of their presumed biogenetic monomeric precursors. Application of the HPLC-MS-MS method successfully proved the enzymatic formation of michellamine C (1c) by in vitro dimerization of korupensamine B (2b).

‘TaClo’, A Chloral-Derived Mammalian Alkaloid with Neurotoxic Properties

Since the discovery that the synthetic compound 1-methyl-4-phenyl-l,2,3,6-tetra-hydropyridine (MPTP, 5) induces parkinsonian-like symptoms in humans, monkeys, and mice, particular attention has been focused on the possible role of environmental toxic agents in causing damage to the central nervous system (Collins et al., 1986).

Escherichia coliProduces Phosphoantigens Activating Human γδ T Cells

Human Vγ9δ2 T lymphocytes are suggested to play an important role in the immune response to various microbial pathogens. In contrast to αβ T cells, γδ T lymphocytes recognize small, non-protein, phosphate-bearing antigens (phosphoantigens) in a major histocompatibility complex-independent manner. Four different phosphoantigens termed TUBag1 to TUBag4 with a common 3-formyl-1-butyl-pyrophosphate moiety and isopentenyl-pyrophosphate have been isolated and identified from mycobacteria. However, natural occurring γδ T cell ligands from other bacterial species were not characterized so far. Here, we describe the structural identification of the two compounds responsible for the γδ T cell-stimulating capacity of Escherichia coli as similar to the mycobacterial phosphoantigens 3-formyl-1-butyl-pyrophosphate and itsM r 275 homologue TUBag2. In addition,E. coli phosphoantigens exert bioactivities on γδ T cells with similar potencies to the mycobacterial phosphoantigens at 5–15 nm concentration. Furthermore, our results clearly prove that the deoxyxylulose 5-phophate pathway (also referred to as Rohmer metabolic route of isoprenoid biosynthesis) is essential for the biosynthesis of the phosphoantigens in E. coli. Because this pathway is absent from human cells, it proves an ideal target for focusing efficiently the antimicrobial selectivity of human γδ T lymphocytes.

E. coli produces phosphoantigens activating human γδ T cells

Human Vγ9δ2 T lymphocytes are suggested to play an important role in the immune response to various microbial pathogens. In contrast to αβ T cells, γδ T lymphocytes recognize small, non-protein, phosphate-bearing antigens (phosphoantigens) in a major histocompatibility complex-independent manner. Four different phosphoantigens termed TUBag1 to TUBag4 with a common 3-formyl-1-butyl-pyrophosphate moiety and isopentenyl-pyrophosphate have been isolated and identified from mycobacteria. However, natural occurring γδ T cell ligands from other bacterial species were not characterized so far. Here, we describe the structural identification of the two compounds responsible for the γδ T cell-stimulating capacity of Escherichia coli as similar to the mycobacterial phosphoantigens 3-formyl-1-butyl-pyrophosphate and itsM r 275 homologue TUBag2. In addition,E. coli phosphoantigens exert bioactivities on γδ T cells with similar potencies to the mycobacterial phosphoantigens at 5–15 nm concentration. Furthermore, our results clearly prove that the deoxyxylulose 5-phophate pathway (also referred to as Rohmer metabolic route of isoprenoid biosynthesis) is essential for the biosynthesis of the phosphoantigens in E. coli. Because this pathway is absent from human cells, it proves an ideal target for focusing efficiently the antimicrobial selectivity of human γδ T lymphocytes.

Nutritional Sources of Novel Tetrahydro-ß-Carbolines

Tetrahydro-s-carboline (THC)-carboxylic acids are readily formed by Pictet-Spengler condensation of tryptophan or tryptamine with various carbonyl compounds. In plants, mammals, and by chemical oxidation studies, it has been demonstrated that THC-carboxylic acids represent precursors of s-carboline (e.g. harman) alkaloids (Herbert and Mann, 1980; Rommelspacher and Susilo, 1985; Bobbitt and Willis, 1980). With respect to Parkinson’s disease, generation of potent neurotoxins from s-carbolines by enzymatic N-methylation has been reported (Collins et al., 1992).