Catalytic deuteration of alkynols and their tetrahydropyranyl ethers

Preparation of Deuterium Labeled Compounds by Pd/C-Al-D2O Facilitated Selective H-D Exchange Reactions

The chemo/regioselective H-D exchange of amino acids and synthetic building blocks by an environmentally benign Pd/C-Al-D₂O catalytic system is described. Due to the importance of isotope labeled compounds in medicinal chemistry and structural biology, notably their use as improved drug candidates and biological probes, the efficient and selective deuteration methods are of great interest. The approach is based on selective H-D exchange reactions where the deuterium source is simple D₂O. D₂ gas is generated in situ from the reaction of aluminum and D₂O, while the commercially available palladium catalyst assists the H-D exchange reaction. The high selectivity and efficiency, as well as the simplicity and safe nature of the procedure make this method an environmentally benign alternative to current alternatives.

Quantitation of Gingerols in Human Plasma by Newly Developed Stable Isotope Dilution Assays and Assessment of Their Immunomodulatory Potential

In a pilot study with two volunteers, the main pungent and bioactive ginger (Zingiber officinale Roscoe) compounds, the gingerols, were quantitated in human plasma after ginger tea consumption using a newly established HPLC-MS/MS(ESI) method on the basis of stable isotope dilution assays. Limits of quantitation for [6]-, [8]-, and [10]-gingerols were determined as 7.6, 3.1, and 4.0 nmol/L, respectively. The highest plasma concentrations of [6]-, [8]-, and [10]-gingerols (42.0, 5.3, and 4.8 nmol/L, respectively) were reached 30-60 min after ginger tea intake. Incubation of activated human T lymphocytes with gingerols increased the intracellular Ca(2+) concentration as well as the IFN-γ secretion by about 20-30%. This gingerol-induced increase of IFN-γ secretion could be blocked by the specific TRPV1 antagonist SB-366791. The results of the present study point to an interaction of gingerols with TRPV1 in activated T lymphocytes leading to an augmentation of IFN-γ secretion.

Oxidative carbon-carbon bond cleavage is a key step in spiroacetal biosynthesis in the fruit fly Bactrocera cacuminata

The early steps of spiroacetal biosynthesis in the fruit fly Bactrocera cacuminata (Solanum fly) have been investigated using a series of deuterium-labeled, oxygenated fatty acid like compounds. These potential spiroacetal precursors were administered to male flies, and their volatile emissions were analyzed for specific deuterium incorporation by GC/MS. This has allowed the order of early oxidative events in the biosynthetic pathway to be determined. Together with the already well-established later steps, the results of these in vivo investigations have allowed essentially the complete delineation of the spiroacetal biosynthetic pathway, beginning from products of primary metabolism. A fatty acid equivalent undergoes a series of enzyme-mediated oxidations leading to a trioxygenated fatty acid like species that includes a vicinal diol. This moiety then undergoes enzyme-mediated oxidative carbon-carbon bond cleavage as the key step to generate the C9 unit of the final spiroacetal. This is the first time such an oxidative transformation has been reported in insects. A final hydroxylation step is followed by spontaneous spiro-cyclization. This distinct pathway adds further to the complexity and diversity of biosynthetic pathways to spiroacetals.

Synthesis and use of stereospecifically deuterated analogues of palmitic Acid to investigate the stereochemical course of the delta11 desaturase of the processionary moth

Thaumetopoea pityocampa pheromone glands contain desaturases that, after several sequential reactions from palmitic acid, catalyze the formation of a unique enyne fatty acid, which is the immediate sex pheromone precursor. In this article, we describe the synthesis of different stereospecifically deuterium-labeled and isotopically tagged palmitic acid probes needed to decipher the stereochemical course of the T. pityocampa Delta(11) desaturase. The synthesis of probes has been carried out by a chemoenzymatic route, in which the key step is the kinetic lipase-catalyzed resolution of racemic mixtures of secondary propargyl alcohols. The presence of the acetylenic bond simplifies the absolute configuration determination of the resolved alcohols. Moreover, it allows the introduction of the isotopic tag by deuteration. By use of the probes thus prepared, experimental evidence is presented that the Delta(11) desaturase of T. pityocampa transforms palmitic acid into (Z)-11-hexadecenoic acid by removal of the pro-(R)-hydrogen atoms from both C11 and C12.

Synthesis of deuterated fatty acids to investigate the biosynthetic pathway of disparlure, the sex pheromone of the Gypsy Moth, Lymantria dispar

The preparation and characterization of a series of deuterium-labeled intermediates used in the study of the biosynthetic pathway for disparlure, the sex pheromone of Lymantria dispar, is reported. The synthetic route starts with propargyl alcohol, and the deuterium atoms are introduced by deuteration of an alkyne precursor in the presence of Wilkinson's catalyst. The olefinic bond was created by the Wittig reaction of a suitable aldehyde with a common tetradeuterated phosphonium ylide intermediate. The presence of the expected label and its correct location were confirmed by both MS and 13C NMR. These compounds were successfully used to elucidate the disparlure biosynthetic pathway.

Quantification of key odorants formed by autoxidation of arachidonic acid using isotope dilution assay

Six odor-active compounds generated by autoxidation of arachidonic acid (AA) were quantified by isotope dilution assay (IDA), i.e., hexanal (1), 1-octen-3-one (2), (E,Z)-2,4-decadienal (3), (E,E)-2,4-decadienal (4), trans-4,5-epoxy-(E)-2-decenal (5), and (E,Z,Z)-2,4,7-tridecatrienal (6). Compound 1 was the most abundant odorant with about 700 mg/100 g autoxidized AA, which corresponds to 2.2 mol% yield. Based on the odor activity values (ratio of concentration to odor threshold), odorants 3 (fatty) and 5 (metallic) showed the highest sensory contribution followed by 1 (green), 2 (mushroom-like), 6 (egg white-like), and 4 (fatty). For the first time, reliable quantitative results are reported for odorants 1-6 in autoxidized AA, in particular odorant 6, which is a characteristic compound found in autoxidized AA. Synthesis of deuterated 6, required for IDA, is described in detail. The formation of odorants 1-6 by autoxidation of AA is discussed with respect to the quantitative data.

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.

Synthesis of deuterated volatile lipid degradation products to be used as internal standards in isotope dilution assays. 1. Aldehydes

The isotopically labeled compounds [5,6-(2)H(2)]hexanal (d-I), [2, 3-(2)H(2)]-(E)-2-nonenal (d-II), [3,4-(2)H(2)]-(E,E)-2,4-nonadienal (d-III), and [3,4-(2)H(2)]-(E,E)-2,4-decadienal (d-IV) were prepared in good yields using new or 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. Synthesis of d-I, d-III, and d-IV has not yet been reported in the literature.

Evidence for intermediate channeling in mitochondrial beta-oxidation

The accumulation of beta-oxidation intermediates was studied by incubating normal and beta-oxidation enzyme-deficient human fibroblasts with [2H4]linoleate and L-carnitine and analyzing the resultant acylcarnitines by tandem mass spectrometry. Labeled decenoyl-, octanoyl-, hexanoyl-, and butyrylcarnitines were the only intermediates observed with normal cells. Intermediates of longer chain length, corresponding to substrates for the beta-oxidation enzymes associated with the inner mitochondrial membrane, were not observed unless a cell line was deficient in one of these enzymes, such as very-long-chain acyl-CoA dehydrogenase, long-chain 3-hydroxyacyl-CoA dehydrogenase, or electron transfer flavoprotein dehydrogenase. Matrix enzyme deficiencies, such as medium- and short-chain acyl-CoA dehydrogenases, were characterized by elevated concentrations of intermediates corresponding to their respective substrates (octanoyl- and decenoylcarnitines in medium-chain acyl-CoA dehydrogenase deficiency and butyrylcarnitine in short-chain acyl-CoA dehydrogenase deficiency). These observations agree with the notion of intermediate channeling due to the organization of beta-oxidation enzymes in complexes. The only exception is the incomplete channeling from thiolase to acyl-CoA dehydrogenase in the matrix. This situation may be a consequence of only one 3-ketoacyl-CoA thiolase being unable to interact with the several acyl-CoA dehydrogenases in the matrix.

Synthesis of ethyl arachidonate-19,19,20,20-d4 and ethyl dihomo-gamma-linolenate-19,19,20,20-d4

Ethyl 5,8,11,14-eicosatetraenoate-19,19,20,20-d4 and ethyl 8,11,14-eicosatrienoate-19,19,20,20-d4 were synthesized by Grignard coupling of the methanesulfonyl ester of 2,5-undecadiyn-1-ol-10,10,11,11-d4 with 5,8-nonadiynoic acid and 8-nonynoic acid, respectively. The coupled products upon Lindlar reduction, followed by the preparation of their ethyl esters, yielded deuteriated ethyl arachidonate and ethyl dihomo-gamma-linolenate, which were completely characterized by 13C and 1H nuclear magnetic resonance and mass spectral analysis.

2-Alkenyl-4,4-dimethyloxazolines as derivatives for the structural elucidation of isomeric unsaturated fatty acids

Several types of unsaturated fatty acid methyl esters were converted into 4,4-dimethyloxazoline (DMOX) derivatives and analyzed by mass spectrometry to further evaluate the feasibility of using this derivative for locating the positions of double bonds in isomeric fatty acids. Five isomeric 20-carbon tetraenoic acids were analyzed in which the four cis double bonds were systematically moved from the 4,7,10,13- to the 8,11,14,17-positions. It was possible to locate the positions of all four double bonds in the 7,10,13,16- and 8,11,14,17-isomers by appropriate ions differing by 12 atomic mass units. In a similar way the three terminal double bonds in the 4,7,10,13-, 5,8,11,14- and 6,9,12,15-isomers could be assigned. Odd-numbered ions at m/z 139, 153 and 167 which are accompanied by an even mass ion at 138, 152 and 166, respectively, are diagnostic for DMOX derivatives of acids with their first double bond, respectively, at positions 4, 5 and 6. It was thus possible to assign the location of all four double bonds in these three isomers. A comparison of the spectra of the DMOX derivatives of 17,17,18,18-d4 vs. 9,10,12,13-d4 linoleic acid suggests that double bonds preferentially migrate toward the polar end of the molecule prior to fragmentation. The merit of using DMOX derivatives to locate double-bond positions in mono- and dicarboxylic acids, produced during beta-oxidation of polyunsaturated fatty acids, was evaluated. The spectra of 3-cis- and 4-cis-decenoic acids differ as do the spectra of 8-carbon dicarboxylic acids with their double bonds at positions 3 and 4.