Francia Arce Vera

Synthesis of Deuterated Volatile Lipid Degradation Products To Be Used as Internal Standards in Isotope Dilution Assays. 2. Vinyl Ketones

The isotopically labeled compounds [5,6-(2)H(2)]-(Z)-1, 5-octadien-3-one (d-I) and [1-(2)H(1;2),2-(2)H(1;1)]-1-octen-3-one (d-II), as well as the unlabeled reference compound (Z)-1, 5-octadien-3-one (I) were prepared by improved synthesis procedures. Labeling position, chemical purity, and isotopic distribution of the compounds were characterized by various MS and NMR techniques. These molecules are used as internal standards in quantification experiments based on isotope dilution assay. The newly prepared compound d-II was synthesized in a simple two-step procedure, and formation of the main isotopomers was studied in model systems.

Automated SPE-RP-HPLC fractionation of biofluids combined to off-line NMR spectroscopy for biomarker identification in metabonomics

NMR-based metabonomics is a valuable and straightforward approach to measuring hundreds of metabolites in complex biofluids. However, metabolite identification is sometimes limited by overlapped signals in NMR spectra. We describe a new methodology using an automated hyphenation of solid phase extraction (SPE) with RP-HPLC combined to NMR spectroscopy, which allowed identification of 72 metabolites of various molecular classes in human urine. This methodology was also successfully applied to the fractionation of a cat urine sample to aid identification of aromatic compounds and felinine. The SPE-RP-HPLC method appears to be a reliable tool to support biomarker discovery in metabonomic studies.

Identification of potent odorants formed by autoxidation of arachidonic acid: structure elucidation and synthesis of (E,Z,Z)-2,4,7-tridecatrienal.

The aroma composition of autoxidized arachidonic acid was characterized by aroma extract dilution analysis. The most potent odorant was trans-4,5-epoxy-(E)-2-decenal followed by 1-octen-3-one, (E,Z)-2,4-decadienal, (E,Z,Z)-2,4,7-tridecatrienal, (E,E)-2,4-decadienal, and hexanal. (E,Z,Z)-2,4,7-Tridecatrienal was unequivocally identified by mass spectrometry and nuclear magnetic resonance (NMR) data. The stereochemistry of its extended double-bond system was elucidated on the basis of NMR measurements. The target compound was synthesized in four steps starting with bromination of 2-octyn-1-ol, followed by copper-catalyzed coupling of the bromide with ethylmagnesium bromide and (E)-2-penten-4-yn-1-ol. Partial hydrogenation of the resulting C(13)-compound with triple bonds in the positions C-4 and C-7 gave rise to (E,Z,Z)-2,4,7-tridecatrien-1-ol, which was finally oxidized to the target compound. It exhibits a typical egg-white-like, marine-like odor at low concentrations, and an intense orange-citrus, animal-like odor at higher concentrations. Its odor threshold was estimated by gas chromatography-olfactometry to be 0.07 ng/L air, which is of the same order of magnitude as that reported for 1-octen-3-one and (E,E)-2,4-decadienal.

Elucidation of Chemical Pathways in the Maillard Reaction by 17O-NMR Spectroscopy

Abstract: 17O‐NMR spectroscopy was employed as an innovative method to help understand mechanistic pathways in sugar fragmentation. Elucidation of reaction mechanisms to final Maillard end products was achieved by starting from specific intermediates obtained by synthesis, such as 1‐deoxy‐d‐erythro‐hexo‐2,3‐diulose. This α‐dicabonyl was thermally treated in the presence of 17O‐enriched water under alkaline conditions. The reaction products were monitored by 17O‐NMR spectroscopy and their structures corroborated by complementary techniques. For the first time, evidence is shown for the direct formation of acetic acid from 1‐deoxy‐d‐erythro‐hexo‐2,3‐diulose by an oxidative α‐dicarbonyl cleavage and incorporation of a 17OH group into the acetic acid released as sugar fragment.