Polysaccharides cyclic

Oxidoreductases Transferases Hydrolases Lyases Isomerases Ligases Phenolic polymers, polyanilines, vinyl polymers Polysaccharides, cyclic oligosaccharides, polyesters Polysaccharides, polyesters, polycarbonates, poly(amino acid)s, polyphosphates... 

Transferases Glycosyltransferase, acyltransferase Polysaccharides, cyclic oligosaccharides, polyesters... 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

In connection with studies on the ring-opening polymerization of cyclic acetals, we have undertaken investigations on the polymerization of bicyclic acetals, bicyclic oxalactone, and bicyclic oxalactam, which yield polysaccharide analogs, macrocyclic oligoesters, and a hydrophilic polyamide, respectively, some of which can be expected to be useful as novel speciality polymers. The monomers employed in the studies were prepared via synthetic routes presented in Scheme 1, starting from 3,4-dihydro-2H-pyran-2-carbaldehyde (acrolein dimer) I. 

To gain an insight into the likely hydrolytic behavior of sulfated simple sugars and polysaccharides, Brimacombe, Foster, Hancock, Overend, and Stacey carried out a rigorous set of experiments with the cyclic sulfates of cyclohexane cis-and trims-1,2-diol as model compounds. The results were interpreted on the reasonable assumption that, in all cases, the cyclic sulfates initially afford a diol monosulfate. Examples of both S-0 and C-0 bond cleavage were encountered. A qualitative reaction mechanism was proposed for use as a working hypothesis for the hydrolysis of sugar sulfates. 

The present Recommendations deal with the acyclic and cyclic forms of monosaccharides and their simple derivatives, as well as with the nomenclature of oligosaccharides and polysaccharides. They are additional to the Definitive Rules for the Nomenclature of Organic Chemistry [13,14] and are intended to govern those aspects of the nomenclature of carbohydrates not covered by those rules. 

Some sugar residues in bacterial polysaccharides are etherified with lactic acid. The biosynthesis of these involves C)-alkylation, by reaction with enol-pyruvate phosphate, to an enol ether (34) of pyruvic acid, followed by reduction to the (R) or (5) form of the lactic acid ether (35). The enol ether may also react in a different manner, giving a cyclic acetal (36) of pyruvic acid. 

Cyclic acetals of pyruvic acid are common in extracellular polysaccharides (compare, for example, Ref. 6). They have also been found in some LPS, namely, those from Shigella dysenteriae type 6 and E. coli 0-149 (Ref. 139), and in the teichoic acid from Brevibacterium iodinum. The biosynthesis of these acetals has already been discussed. 

F.a.b.-m.s. has been applied to three types of problem in the bacterial polysaccharide area assigning compositions (including the number and type of O-acyl groups), sequencing, and identifying cyclic structures. The last application is covered in Section VI,5. 

Data from f.a.b.-m.s., and also f.d.-m.s., revealed the existence of naturally occurring, large cyclic polysaccharides. The first indication that a molecule may be cyclic comes from its precise molecular-weight determination. Cyclic molecules are 18 mass units less than their linear counterparts. Loss of water may, of course, occur in a number of ways, for example, by dehydration or lactonization, and conclusive evidence for the presence of a cyclic molecule can only be obtained from f.a.b.-m.s. of suitable derivatives, such as the permethyl derivative. Cyclic and dehydrated linear polymers are distinguishable after permethylation, as the cyclic polymer will incorporate one methyl group less than the linear molecule. 

The synthesis of block copolymers of polysaccharides and aliphatic polyesters has also been tried. But, many successful results were not reported because the reactivity of many hydroxyl groups on polysaccharides was an obstacle to the ROP of cyclic polyester or coupling reactions using terminal-activated polysaccharides. Li and Zhang reported the synthesis of maltoheptaose-b-PCL copolymers by ROP... 

The biological availability of contaminating and naturally occurring organic compounds can be estimated by finding their solubility in water. The more soluble the compound, the more available it is for decomposition. While this is true for most organic compounds, there are some that are soluble but also recalcitrant to decomposition. This is the result of complex, sometimes multi-cyclic, structures that inhibit decomposition, such as those of polysaccharides and lignins [2],... 

Other cyclic acetals that have been studied are 1,3,5-trioxane, 1,3,5-trioxepane, 1,3,6,9-tetraoxacycloundecane, and 1,3,5,7-tetroxocane (also referred to as 1,3,5,7-tetroxane) [Kawakami and Yamashita, 1979 Munoz-Escalona, 1978 Schulz et al., 1984 Szwarc and Perrin, 1979]. Polymerization of bicyclic acetals has been of interest for synthesizing polysaccharides [Good and Schuerch, 1985 Hirasawa et al., 1988 Okada, 1991 Okada et al., 1989 Sumitomo and Okada, 1984]. 

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