Glucan
A glucan is a polysaccharide derived from D-glucose, linked by glycosidic bonds. Many beta-glucans are medically important. They represent a drug target for antifungal medications of the echinocandin class. Types. The following are glucans: Properties. Properties of glucans include resistance to oral acids/enzyme and water insolubility. Glucans extracted from grains tend to be both soluble and insoluble. Structure. Glucans are polysaccharides derived from glucose monomers. The monomers are linked by glycosidic bonds. Four types of glucose-based polysaccharides are possible: 1,6- (starch), 1,4- (cellulose), 1,3- (laminarin), and 1,2-bonded glucans. 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--mannopyranoses). A wide range of unique monomers with different radical R can be synthesized. There were synthesized polymers with R= -CH, -CHCHCH, and -CHCH. 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. 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= -CHCH) functionalized polymer. Polymerization of 3,4-epoxy levoglucosan (1,6;3,4-dianhydro-2-O-alkyl-β--galactopyranose) 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.