Glucan

 ( Polysaccharides ) 

A glucan molecule is a polysaccharide of D-glucose monomers, linked by .

Many are medically important. They represent a drug target for antifungal medications of the echinocandin class.

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Types The following are glucans: (The α- and β- and numbers clarify the type of O-glycosidic bond.)

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Alpha

• dextran, α-1,6-glucan with α-1,3-branches
• floridean starch, α-1,4- and α-1,6-glucan
• glycogen, α-1,4- and α-1,6-glucan
• pullulan, α-1,4- and α-1,6-glucan
• starch, a mixture of amylose and amylopectin, both α-1,4- and α-1,6-glucans

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Beta

• cellulose, β-1,4-glucan
• chrysolaminarin, β-1,3-glucan
• curdlan, β-1,3-glucan
• laminarin, β-1,3- and β-1,6-glucan
• lentinan, a strictly purified β-1,6:β-1,3-glucan from Lentinus edodes
• lichenin, β-1,3- and β-1,4-glucan
• oat beta-glucan, β-1,3- and β-1,4-glucan
• pleuran, β-1,3- and β-1,6-glucan isolated from Pleurotus ostreatus
• zymosan, β-1,3-glucan

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Properties Properties of glucans include resistance to oral acids/enzyme and water insolubility. Glucans extracted from grains tend to be both soluble and insoluble.

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Chemistry of Glucans Glucans are of glucose monomers linked by glycosidic bonds. Accordingly, polymers built up of carbohydrate units bound by bonds other than glycosodic bonds are not considered polysaccharides. Only four different types glucose-based polysaccharides are possible to be built: 1,6- (starch), 1,4- (cellulose), 1,3- (laminarin) and 1,2-bonded glucans.

Levoglucosan is 1,6-anhydro derivative of glucose. It is one of the key products in thermal conversion of polysaccharides. Polysaccharides are not volatile at combustion temperatures; propagation of fire takes place due to combustion of volatile products of degradation of polysaccharides, mainly levoglucosan.

The first representatives of main chain unhydrolysable linear polymers made up of levoglucosan units were synthesized in 1985 by anionic polymerization of 2,3-epoxy derivatives of levoglucosan (1,6;2,3-dianhydro-4-O-alkyl-β-D-mannopyranoses).Berman, E.L., Gorkovenko A.A., Zubov, V.P., and Ponomarenko, V.A.,"Regio and Stereospecific Synthesis of Polyglucose with Novel Type Bond''Soviet J.Bioorg. Chem. 11 (1985), 1125-1129

A wide range of unique monomers with different radical R can be synthesized. There were synthesized polymers with R= -CH₃, -CH₂CHCH₂,Gorkovenko, A.A., Berman, E.L., and Ponomarenko, V.A. ''Polymerization of 1, 6;2,3 dianhydro 4 O allyl β D manno¬pyranose" Vysocomol. Soed., Ser. B, 1987, 29, 134 137 and -CH₂C₆H₅.Gorkovenko, A.A., Berman, E.L., and Ponomarenko, V.A. "A New Polymer of Glucose. Poly(2 3) D glucose" Soviet J. Bioorg. Chem., 1987, 13, 218 222 Investigation of the polymerization kinetics of those derivatives, molecular weight and molecular-weight distribution showed that the polymerization has the features of a living polymerization system. The process takes place without termination and transfer of the polymer chain with a degree of polymerization equal to the mole ratio of the monomer to the initiator.Berman, E.L., Gorkovenko, A.A., Rogozhkina, E.D., Izumnikov, A.A., and Ponomarenko, V.A. “Kinetics and Mechanism of Epoxy Ring-Opening Polymerization of 1,6;2,3-Dianhydro-4-O-alkyl-b-D-mannopyranoses” Polymer Sci. USSR, 1988, 413-418Berman E.L. Gorkovenko, A.A., Rogozhkina, E.D., Izyumnikov, A.L., and Ponomarenko, V.A. "Synthesis of Chiral Derivatives of Poly(Ethylene Oxide)" Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 705 707 Accordingly, the upper value molecular weight polymer determines only degree of purification system what determine the presence in the system uncontrollable amount of terminators of polymer chains.

Poly(2-3)-D-glucose was synthesized proceeds by transformation of benzyl (R= -CH₂C₆H₅) functionalized polymer.

Polymerization of 3,4-epoxy levoglucosan (1,6;3,4-dianhydro-2-O-alkyl-β-D-galactopyranose) Gorkovenko A. A., Berman, E.L., and Ponomarenko, V.A., Poly(3 4) 2 O methyl 1,6 anhydro b D glucopyranose. The First Example of (3 4) linked Polymer Carbohydrates" Soviet J. Bioorg. Chem. 12 (1986), 514-520 results in formation 3,4-bounded levoglucosan polymer.

The presence of 1,6-anhydro structure in every unit of polymer chains allows researchers to apply all spectra of well developed methods of carbohydrate chemistry with formation of highly intriguing biological application polymers. The polymers are the only known regular polyethers built up of carbohydrate units in main polymer chain.Berman E.L., Gorkovenko, A.A., and Ponomarenko, V.A. "Structure and Polymerizability of 1,6;2,3 and 1,6;3,4¬ Dianhydrohexapyranoses" Polymer Sci. USSR, 1988, 30, 497¬-502Berman, E.L., “New Glucose Polymers” in “Levoglucosenone and Levoglucosanes: Symposium: 204th National meeting”, Zbigniew J. Witczak (editor), American Chemical Society. Division of Carbohydrate Chemistry, 189-214. Publisher: A T L Press, Scientific Publishers

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See also

• Glucanase

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