Radicals carbohydrate

Polyethylene (Section 6 21) A polymer of ethylene Polymer (Section 6 21) Large molecule formed by the repeti tive combination of many smaller molecules (monomers) Polymerase chain reaction (Section 28 16) A laboratory method for making multiple copies of DNA Polymerization (Section 6 21) Process by which a polymer is prepared The principal processes include free radical cationic coordination and condensation polymerization Polypeptide (Section 27 1) A polymer made up of many (more than eight to ten) amino acid residues Polypropylene (Section 6 21) A polymer of propene Polysaccharide (Sections 25 1 and 25 15) A carbohydrate that yields many monosacchande units on hydrolysis Potential energy (Section 2 18) The energy a system has ex elusive of Its kinetic energy... 

One of the important consequences of neuronal stimulation is increased neuronal aerobic metabolism which produces reactive oxygen species (ROS). ROS can oxidize several biomoiecules (carbohydrates, DNA, lipids, and proteins). Thus, even oxygen, which is essential for aerobic life, may be potentially toxic to cells. Addition of one electron to molecular oxygen (O,) generates a free radical [O2)) the superoxide anion. This is converted through activation of an enzyme, superoxide dismurase, to hydrogen peroxide (H-iO,), which is, in turn, the source of the hydroxyl radical (OH). Usually catalase... 

Vasella has used deoxy-nitro sugars for the synthesis of various biologically important carbohydrates, and the radical nitromethyladon of deoxy-nitro sugars has been used for synthesis of fnictose 6-phosphate" and 6-C-methyl and 6-C-rhydroxymethyl analogiies of iV-acetylnenraitinic acid fsee Scheme7.2. ... 

O-Isopropylidene derivatives of carbohydrates form structural isomers from carbohydrates which themselves are epimers. Since structural isomers often fragment differently whereas epimers do not, mass spectra of these derivatives may permit interpretation in terms of stereochemistry. Although molecular-ion peaks are not observed, the molecular weight can be determined readily from a relatively intense M-CH/ peak, resulting from loss of a methyl radical from a 1, 3-dioxolane ring (12). 

Fischer projection, 975-978 carbohydrates and, 977-978 D sugars, 980 i., sugars, 980-981 rotation of, 976 R.S configuration of, 977 conventions for, 975-976 Fishhook arrow, radical reactions and, 139, 240... 

In another version of this method, the radical generated by radical exchange from the aryl telluride carbohydrate 83 and the N-acetoxy-2-thiopyridone affords, after intramolecular cyclization and desulfanylation, the polyhydroxylated and phosphorylated pseudo sugar 84 [54] (Scheme 23). 

This enzyme catalyzes the conversion of pyruvate to formate and acetyl CoA and is a key enzyme in the anaerobic degradation of carbohydrates in some Enterobacteriaceae. Using an enzyme selectively C-labeled with glycine, it was shown by EPR that the reaction involves production of a free radical at C-2 of glycine (Wagner et al. 1992). This was confirmed by destruction of the radical with O2, and determination of part of the structure of the small protein that contained an oxalyl residue originating from gly-734. 

Attack of the OH radical on carbohydrates of low molecular mass gives rise to a variety of products. Indeed, the reaction of radiolytically-generated OH radical with lower hexose sugars produces lower saccharides (for di- and higher saccharide species), uronic and aldonic acids, and 3-, 2- and 1-carbon aldehydic fragments, e.g. 

Typical spectra obtained are shown in Fig. 1.2. Moreover, substantial radiolytically-mediated elevations in the concentration of serum formate, arising from the oxidation of carbohydrates present by OH radical, were also detectable. In addition to the above modifications, 7-radiolysis of inflammatory knee-joint synovial fluid generated an oligosaccharide species of low molecular mass derived from the radiolytic fragmentation of hyaluronate as outlined in the previous section dealing with oxidative damage to carbohydrates. The... 

The complex cascades that comprise the inflammatory reaction are designed primarily to limit tissue damage and prevent or inhibit infection. ROMs play a critical role in both these beneficial processes. However, high level fluxes of toxic free radicals are capable of causing damage to diverse biomolecules, including lipids, proteins, DNA and carbohydrates (discussed below). 

Scheme 10.17 illustrates allylation by reaction of radical intermediates with allyl stannanes. The first entry uses a carbohydrate-derived xanthate as the radical source. The addition in this case is highly stereoselective because the shape of the bicyclic ring system provides a steric bias. In Entry 2, a primary phenylthiocar-bonate ester is used as the radical source. In Entry 3, the allyl group is introduced at a rather congested carbon. The reaction is completely stereoselective, presumably because of steric features of the tricyclic system. In Entry 4, a primary selenide serves as the radical source. Entry 5 involves a tandem alkylation-allylation with triethylboron generating the ethyl radical that initiates the reaction. This reaction was done in the presence of a Lewis acid, but lanthanide salts also give good results. 

The chemical origin of free radicals in coffee is attributed to the sugars or carbohydrates, rather than phenolic constituents100. 

Haase C, Seitz O (2007) Chemical Synthesis of Glycopeptides. 267 1-36 Hahn F, Schepers U (2007) Solid Phase Chemistry for the Directed Synthesis of Biologically Active Polyamine Analogs, Derivatives, and Conjugates. 278 135-208 Hansen SG, Skrydstrup T (2006) Modification of Amino Acids, Peptides, and Carbohydrates through Radical Chemistry. 264 135-162... 

Moreover, the reaction with Y = OCH3 and the stereochemical control of analogous hex-5-enyl radical cyclizations has also been studied. This method constitutes part of a synthetic route from carbohydrates to optically active carbocycles.[74],[75]... 

The most radical change of classification in this group is the abandonment of Levene s1 definition that the carbohydrate group of all... 

The laccase molecule is a dimeric or tetrameric glycoprotein, which contains four copper atoms per monomer, distributed in three redox sites. More than 100 types of laccase have been characterized. These enzymes are glycoproteins with molecular weights of 50-130 kDa. Approximately 45% of the molecular weight of this enzyme in plants are carbohydrate portions, whereas fungal laccases contain less of a carbohydrate portion (10-30%). Some studies have suggested that the carbohydrate portion of the molecule ensures the conformational stability of the globule and protects it from proteolysis and inactivation by radicals (Morozova and others 2007). 

The observation of a stereoconvergent cyclization by Roy et al. [18], as shown in the third example, is of special interest from a synthetic point of view because it exploits the configurational lability of radicals in a favorable manner. The other examples, i. e. Nugent and RajanBabu s cyclization of a carbohydrate-derived epoxide [5d] and Clive s quinane synthesis [19], amply demonstrate the usefulness of the titanocene-initiated epoxide opening. 

His present interests include the development of new synthetic methodologies in carbohydrates, free radical chemistry, organometallic chemistry (Pauson-Khand reaction, transition metal (PtCl2, AuCl)-mediated cycloisomerization of polyunsaturated precursors), and synthesis/biologi-cal evaluation of heterocyclic systems (CSIC reaction, tacrine analogs). 

Although the generation of nitroalkyl radicals by oxidative transition-metal-mediated reactions is known for many years, their application in carbohydrate chemistry was not investigated until recently.41... 

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