Hydrophilically functionalized pyrazoles from sugars11Enantiopure Building Blocks from Sugars. Part 22. For Part 21, see Ref.[1].—Presented, in part, at the 9th European Carbohydrate Symposium, Utrecht, The Netherlands, July 1997; Abstract E1

N-Arylations of trifluoromethylated N-acylhydrazones with diaryliodonium salts as arylation reagents

A novel and efficient N-arylation of trifluoromethylated N-acylhydrazones is described by using diaryliodonium salts as arylation reagents in the presence of copper salts. A wide variety of N-aryl acylhydrazones are obtained with good to excellent yields under mild reaction conditions.

Formation of Reactive Intermediates, Color, and Antioxidant Activity in the Maillard Reaction of Maltose in Comparison to d-Glucose

In this study, the Maillard reaction of maltose and d-glucose in the presence of l-alanine was investigated in aqueous solution at 130 °C and pH 5. The reactivity of both carbohydrates was compared in regards of their degradation, browning, and antioxidant activity. In order to identify relevant differences in the reaction pathways, the concentrations of selected intermediates such as 1,2-dicarbonyl compounds, furans, furanones, and pyranones were determined. It was found, that the degradation of maltose predominantly yields 1,2-dicarbonyls that still carry a glucosyl moiety and thus subsequent reactions to HMF, furfural, and 2-acetylfuran are favored due to the elimination of d-glucose, which is an excellent leaving group in aqueous solution. Consequently, higher amounts of these heterocycles are formed from maltose. 3-deoxyglucosone and 3-deoxygalactosone represent the only relevant C₆-1,2-dicarbonyls in maltose incubations and are produced in nearly equimolar amounts during the first 60 min of heating as byproducts of the HMF formation.

The role of effective leaf mixing length in the relationship between the δ18 O of stem cellulose and source water across a salinity gradient

Previous mangrove tree ring studies attempted, unsuccessfully, to relate the δ(18) O of trunk cellulose (δ(18) O(CELL) ) to the δ(18) O of source water (δ(18) O(SW) ). Here, we tested whether biochemical fractionation associated with one of the oxygen in the cellulose glucose moiety or variation in leaf water oxygen isotope fractionation (Δ(LW) ) can interfere with the δ(18) O(SW) signal as it is recorded in the δ(18) O(CELL) of mangrove (saltwater) and hammock (freshwater) plants. We selected two transects experiencing a salinity gradient, located in the Florida Keys, USA. The δ(18) O(CELL) throughout both transects did not show the pattern expected based on that of the δ(18) O(SW) . We found that in one of the transects, biochemical fractionation interfered with the δ(18) O(SW) signal, while in the other transect Δ(LW) differed between mangrove and hammock plants. Observed differences in Δ(LW) between mangroves and hammocks were caused by a longer effective leaf mixing length (L) of the water pathway in mangrove leaves compared to those of hammock leaves. Changes in L could have caused the δ(18) O(CELL) to record not only variations in the δ(18) O(SW) but also in Δ(LW) making it impossible to isolate the δ(18) O(SW) signal.

Novel insights into the maillard catalyzed degradation of maltose

Numerous investigations concerning Maillard degradation of carbohydrates clearly depict the important impact of α-dicarbonyl compounds on changes occurring during preparation of food or physiological processes in vivo. To study the formation of these reactive intermediates during degradation of maltose in the presence of lysine, α-dicarbonyl compounds were isolated, identified and quantified after reaction with o-phenylenediamine to form their stable quinoxaline derivatives. Maltosone and 1,4-dideoxyglucosone were synthesized and incubated independently with lysine to investigate follow-up products and to gain further insights into the complex degradation mechanisms. Glyoxylic acid as a dicarbonyl structure and 5,6-dihydroxy-2,3-dioxohexanal as a 1,2,3-tricarbonyl compound were established as novel Maillard degradation products of maltose. Conducted experiments unequivocally demonstrated that inter- and intramolecular redox reactions are of major importance during degradation of disaccharides. 1,4-Dideoxyglucosone, 1-lysino-1,4-dideoxyglucosone, 5,6-dihydroxy-2,3-dioxohexanal, 3,4-dideoxypentosone and glyoxylic acid were found to be the central intermediates involved in the redox chemistry. With the present study we deliver a comprehensive overview on the mechanisms behind α-dicarbonyl compounds evolving from Maillard degradation of maltose.

Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects

The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3-6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose.

Unsaturated O- and N-heterocycles from carbohydrate feedstocks

With reference to the impending transition of chemical industry from depleting fossil raw materials to renewable feedstocks--the end of cheap oil is predicted for 2040 at the latest--this account gives an overview on chemically transforming carbohydrates, by far the major part of the annually regrowing biomass, into the following unsaturated O- and N-heterocycles with versatile industrial application profiles: furans, pyrans, dihydropyranones, pyrroles, pyrazoles, imidazoles, pyridinols, pyrazines, and quinoxalines. Although the emphasis was laid on conversions that can be effected in practical one-pot procedures or in a few large-scale-adaptable steps, a broad structural variety of products emerges that have not only diverse chemical functionalities but also hydrophilic "residual sugar" portions that render them water-soluble and readily biodegradable.

Novel reversion reaction of D-arabino-hexose phenylosotriazole. A useful model in natural glycoside and polysaccharide analysis

Treatment of D-arabino-hexose phenylosotriazole with conc. hydrochloric acid afforded a new type of alpha- and beta-glycosides of D-erythrose formed by reaction of the 3,6-anhydro derivative with the in situ formed 2-phenyl-4-(formylmethyl)- 1,2,3-triazole.

Isolation and identification of the intermediates during pyrazole formation of some carbohydrate hydrazone derivatives

Reaction of the oxidation product of L-ascorbic acid, dehydro-L-ascorbic acid, with o-phenylenediamine, followed by 2,4,6-trichlorophenylhydrazine (3) afforded 3-[1-(2,4,6-trichlorophenylhydrazono)-L-threo-2,3,4-trihydroxybut-1-yl]quinoxalin-2(1H)one (4), whose structure was deduced from studying its periodate oxidation, which gave the glyoxal derivative 3-[1-(2,4,6-trichlorophenylhydrazono)glyoxal-1-yl]quinoxalin-2(1H)one (5) that upon reduction afforded 3-[1-(2,4,6-trichlorophenylhydrazono)-2-hydroxyethy-1-yl]quinoxalin-2(1H)one (6). The reaction of 5 with 3 afforded the bishydrazone 3-[1,2-bis(2,4,6-trichlorophenylhydrazono)glyoxal-1-yl]quinoxalin-2(1H)one. The reaction of 5 with acetic anhydride in pyridine afforded the 2,3-dihydrofuro[2,3-b]quinoxaline derivative 2-acetoxy-3-[2-acetyl-2-(2,4,6-trichlorophenyl)hydrazono)]-2,3-dihydrofuro[2,3-b]quinoxaline. Acetylation of 4 with acetic anhydride in pyridine afforded the acyclic diacetate intermediate 3-[3,4-di-O-acetyl-2-deoxy-1-(2,4,6-trichlorophenylhydra-zono)but-2-en-1-yl]quinoxalin-2(1H)one (12), which was also obtained from the reaction of 4 with boiling acetic anhydride. Compound 12 rearranged under the reaction conditions to give the pyrazole derivatives 3-[5-(ace-toxymethyl)-1-(2,4,6-trichlorophenyl)pyrazol-3-yl]quinoxalin-2(1H)one (14) and 2-acetoxy-3-[5-(acetoxymethyl)-1-(2,4,6-trichlorophenyl)pyrazol-3-yl)]quinoxaline (15), as well as the 2,3-dihydrofuro[2,3-b]quinoxaline derivative 2-(2-acetoxyethen-2-yl)-3-[2-(2,4,6-trichlorophenyl)hydrazono]-2,3-dihydrofuro[2,3-b]quinoxaline. Acetylation of 3-[5-(hydroxymethyl)-l-(2,4,6-trichlorophenyl)pyrazol-3-yl]quinoxalin-2(1H)one (16) with acetic anhydride in pyridine or 12 with boiling acetic anhydride afforded 15 and 16, respectively. Treatment of 4 with diluted sodium hydroxide afforded the pyrazolo[2,3-b]quinoxaline (flavazole) derivative 1-(2,4,6-trichlorophenyl)-3-(L-threo-glycerol-1-yl)pyrazolo[2,3-b]quinoxaline whose acetylation afforded the acetyl derivative 3-(2,3,4-tri-O-acetyl-L-threo-glycerol-1-yl)-1-(2,4,6-trichlorophenyl)pyrazolo[2,3-b]quinoxaline. The assigned structures were based on spectral analysis. The activity of compound 4 against hepatitis B virus has been studied.