A-d- -glycoside bonds

Vitamin Bi2 is a D-ribofuranose derivative, and the structure of vitamin B12 5 -phosphate, a precursoi 11 of vitamin B12, has been determined. The a-D-glycosidic bond lies 16° (0.51 A) out of the plane of the 5,6-dimethylbenzimidazole ring, because of steric or nonbonded interactions. The D-ribofuranose moiety has that envelope conformation having C-2 exo (0.77 A exoplanar) C-3 and C-5 bear phosphate groups. 

Pullulanase Hydrolysis of 1,6-a-D-glycosidic bonds on amylopectin and glycogen and in a- and (3-limit dextrins, yielding linear polysaccharides. 

Maltose consists of two glucose units linked via a (1-4)- a-D-glycosidic bond ... 

Starch is a high molecular-weight polymer of anhydroglueose units linked by a-D-glycosidic bonds. The two main constituents of stareh are amylose and amylopectin (Fig. 8.6). Amylose is a linear molecule with an extended helieal twist and generally has a moleeular weight of 1.0 to 1.5 million. Amylopeetin is... 

Suciose [57-50-1] (P-D-fructofuianosyl-a-D-glucopyianoside), 0 2 22, fomiula weight 342.3, is a disaccharide composed of glucose and fmctose residues joined by an a,P-glycosidic bond (Fig. 1). 

Most nucleosides contain D-ribose or 2-deoxy-D-ribose linked to N-1 of a pyrimidine or to N-9 of a purine by a P-glycosidic bond whose syn conformers predominate. 

Two new sugars were linked by a C-glycosidic bond p-D-ribopyranoside in Passiflora and p-D-6-deoxygulopyranoside in Viola. A 3,6,8-tri-C-xylosylflavone was isolated from Asplenium. ... 

Deoxyadenosine is 9-2 -deoxy-/3-D-ribofuranosyladenine, or 2-deoxy-D-ribose linked through a /3-glycosidic bond from N-9 of the base to C-l of the sugar. Thus, its structure is... 

Nucleic acids are biopolymers present in every living cell, with monomeric units consisting of a carbohydrate linked via a p-D-glycosidic bond to a heterocyclic base and interconnected by phosphodiester bonds at positions C-3 and C-5. The monomeric units of nucleic acids can be considered the nucleotides that are formed from a carbohydrate residue connected to the base by the p-D-glycosidic bond and to a phosphate group at C-5. The molecules derived from nucleotides by removing the phosphate group are the nucleosides. 

It should be pointed out, however, that there are exceptions to the rule, such as the hydrolysis of the anomeric methyl pyranosides of 3,6-anhydro-2,4-di-0-methyl-D-glucose, in which the a-D anomer is hydrolyzed 30 times as fast as the /3-d anomer [which has a slightly distorted 1B d) conformation having the glycosidic bond in the equatorial position]. The faster hydrolysis of the a-D glycoside has been attributed to the great strain in all of the possible conformations of this compound. ... 

The n.m.r. spectra of the previously reported comb-like derivatives prepared by orthoester- and Helferich-type condensations of D-glucose on to amylose have been recorded. It was known from monomeric studies that the orthoester method favoured the /3-D-glycosidic bond, whereas the Helferich method favoured the o-D-glycosidic bond. The spectra confirmed that 4,6-disubstitution occurred on the D-glucose residues of amylose and that a degree of polymer linearity existed but the spectra also indicated that extensive, if not exclusive, -D-glucosylation occurred with both condensation methods. 

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