The metabolic and biochemical impact of glucose 6-sulfonate (sulfoquinovose), a dietary sugar, on carbohydrate metabolism.

Increased activity of the main carbohydrate pathways (glycolysis, pentose phosphate, and hexosamine biosynthetic pathways) is one of the hallmarks of metabolic diseases such as cancer. Sulfoquinovosyl diacylglycerol is a sulfoglycolipid found in the human diet that possesses anticancer activity that is absent when its carbohydrate moiety (glucose 6-sulfonate or sulfoquinovose) is removed. This work used bacterial systems to further understand the metabolism of this sugar through three main carbohydrate processing pathways and how this could influence its biological activity. Using (13)C NMR spectroscopy and enzyme assays, we showed that glucose 6-sulfonate cannot enter the pentose phosphate pathway, hence decreasing pentose and nucleotide biosyntheses. In glycolysis, glucose 6-sulfonate only provides one pyruvate per monosaccharide molecule, decreasing the flux of this pathway by half when compared to glucose 6-phosphate. Glucose 6-sulfonate can enter the hexosamine biosynthetic pathway by producing glucosamine 6-sulfonate, which is a reported antibacterial agent that competitively inhibits hexosamine production. All these interactions with carbohydrate routes might help explain the observed anticancer activity that glucose 6-sulfonate has in vitro. This adds to our knowledge of how vegetables rich in glucose 6-sulfonate can also act as metabolic inhibitors of pathways that are increased in metabolic diseases.

Synthesis and evaluation of an N-acetylglucosamine biosynthesis inhibitor.

The structural rationale, synthesis and evaluation of an inhibitor designed to block glucosamine synthesis by competitively inhibiting the action of glutamine: fructose-6-phosphate amidotransferase and subsequently reducing the transformation of any glucosamine-6-phosphate formed to UDP-N-acetylglucosamine are described. The inhibitor 2-acetamido-2,6-dideoxy-6-sulfo-D-glucose (D-glucosamine-6-sulfonate) is an analog of glucosamine-6-phosphate in which the phosphate group in the latter is replaced with a sulfonic acid group. The inhibitor is designed to function by three different modes which together reduce UDP-N-acetylglucosamine synthesis. This reduction was confirmed by evaluating the effect of the inhibitor on bacterial cell-wall synthesis and by demonstrating that it inhibits acetylation of glucosamine-6-phosphate competitively and by acting as a surrogate substrate. Inhibition of glucosamine production or suitably activated glucosamine in bacteria leads to disruption of the peptidoglycan structure, which results in softening, bulging, deformation, fragility and lysis of the cells. These modifications were documented by scanning electron microscopy for bacteria treated with the inhibitor. They were observed for inhibitor concentrations in the 20 mg/mL range for Escherichia coli and Bacillus subtilis and the 5 mg/mL range for Rhizobium trifolii.

The Lan3-2 glycoepitope of Hirudo medicinalis consists of beta-(1,4)-linked mannopyranose: cell type-specific glycans of H. medicinalis.

While glycosyltransferases are restrictively expressed in invertebrate model organisms, little is known of their glycan end products. One such restrictively expressed glycoepitope was localized to sensory and epithelial cells of leech and Caenorhabditis elegans using the Lan3-2 monoclonal antibody. A biological function for the neural Lan3-2 epitope was previously determined in the leech. Here we report on the chemical structure of this mannosidic epitope harvested from whole Hirudo medicinalis. Crude glycans were liberated from glycoproteins by hydrazinolysis. Re-N-acetylated glycans were subjected to immunoaffinity purification. The affinity-purified glycans were fractioned by size chromatography into oligosaccharides and polysaccharides. Lan3-2 oligosaccharide structure was characterized by gas chromatography of alditol acetates, methylation analysis, 500 MHz 1H NMR spectroscopy, matrix-assisted laser desorption/ionization mass spectrometry, and electrospray ionization tandem MS-MS of permethylated derivatives. The predominant components of the Lan3-2 oligosaccharide fraction were a series of linear beta-(1,4)-linked mannose polymers. The homologous expression of the Lan3-2 epitope in C. elegans will facilitate the exploration of its glycosylation pathway. Other invertebrates expressing the Lan3-2 epitope are Planaria dugesia, Capitella sp. I and Lumbriculus variegatus. The glycoepitope was not detected in the diploblastic animals Hydra littoralis and Aptaisia sp. or in deuterostomes.

Design and evaluation of dihydroxytetrahydro-1H-pyrrolo[2,1-c]- [1,4]benzothiazines as conformationally restricted transition-state inhibitors of beta-ribosidases.

[structure: see text] The preparation of three new chiral thiazines from ribose is described. Two of these are dihydroxytetrahydro-1H-pyrrolo[2,1-c][1,4]benzothiazines with iminopentitol substructures corresponding to the L-lyxo and D-ribo configurations. They were designed to present a favorable transition-state mimic for the inhibition of ribosidases. This new thiazine class opens the way to the development of new inhibitors to carbohydrate processing enzymes of therapeutic importance such as nucleoside hydrolases and purine nucleoside phosphorylases.

Accumulation of high-molecular-weight amylose in Alzheimer's disease brains.

Although most of the glucose metabolized in the brain is taken up from the blood, glucose derived from glycogen stores is increasingly implicated in both normal brain function and injury repair. An impaired glucose metabolism is one of the features of Alzheimer's disease (AD) entailing a reduction in glucose transporters and the uptake of glucose as well as alterations in the specific activity of glycolytic enzymes. Here we report that AD brains accumulate amylose, the unbranched alpha(1,4)-linked glucose polymer that is resistant to degradation by glycolytic enzymes. Neutral polysaccharides harvested from postmortem brains were purified with hydrazinolysis, ion exchange, and sizing chromatography and subjected to NMR spectroscopy, GC, GC-MS, and methylation analysis. Five percent of the polysaccharides (50 micro g [0.3 micro mol]/g wet weight brain tissue) consisted of amylose with molecular weights exceeding 600,000 Da. There is no evidence for 1,6-branching, indicating that the polymer is not a form of high-molecular-weight glycogen. By GC analysis, the glucose content of the AD brains was almost three times greater than that of the age-matched control brains. A synthesis of amylose in AD brains at the expense of glycogen would compromise glucose metabolism and enhance neural degeneration.

Remote site bromination via a cascade rearrangement involving two bridging dioxonium species during oxidative cleavage of a benzylidene acetal.

Attempted cleavage of the benzylidene group of 3,5-O-benzylidene-2,6,7-tri-O-trimethylacetyl-D-glycero-D-gulo-heptono-1,4-lactone with N-bromosuccinimide led to the formation of a 7-bromo derivative with a benzoyl group in the 3-position and trimethylacetyl groups in the 5 and 6 positions. Analysis of the coupling constants in the proton NMR spectra indicated that both trimethylacetyl groups had participated to shift the crowded electron-deficient center formed at the 5-position by the decomposition of the bromobenzylidene group to the much more accessible 7-position. The net result of this cascade rearrangement was retention at both the C-5 and C-6 positions. This is an interesting example of a cascade rearrangement under strict entropic and stereo control the synthetic utility of which is being investigated.

The use of the o-nitrophenyl group as a protecting/activating group for 2-acetamido-2-deoxyglucose.

The o-nitrophenyl group, a protecting group with latent activation potential, was used as a protecting group for the glycosidic position. It is stable to common conditions used in synthesis and can be activated for displacement and glycoside formation by an alcohol, using zinc chloride as a catalyst. Good to excellent yields of beta-glycosides of the important amino sugar N-acetylglucosamine were obtained. A mechanism for the reaction is proposed.