Anomer

Abstract: Publisher Summary This chapter examines the carbon-13 nuclear magnetic resonance spectroscopy of polysaccharides. The C-1 resonances of the pyranoid forms of glucose, xylose, galactose, arabinose, methyl glucoside, and methyl xyloside are shown to be sensitive to the anomeric configuration. The C-1 chemical-shifts of furanosides are generally at lower field than those of their anomeric counterparts in the pyranose series. The values of a series of α- and β-shifts have been determined for mono- O -methylglucoses and mono- O -methylmannoses to aid in the assignments of 13 C signals of oligosaccharides and polysaccharides consisting of glucose and mannose respectively. The 13 C-NMR spectra of polysaccharides having mixed linkages can sometimes be interpreted by the reference to the spectra of homopolymers representing each type of linkage. The C-2 to C-6 signals of monorhamnomannan were rationalized by gauging substitution-shifts and by the use of D -glucose precursors labeled with 2 H or 13 C. Glucose gave a rhamnomannan whose spectrum lacked the signal at 66.7, characterizing it as from C-6. The polysaccharides containing 3-deoxy- D -manno-octulosylonic acid residues are also elaborated.

Abstract: Historical Aspects and Definitions Origin and Consequences of the Anomeric Effect Theoretical Studies of the Anomeric Effect Stereoelectronic Effects Associated with the Anomeric Effect Endo and Exo Anomeric Interactions The Enthalpic Anomeric Effect Second- and Lower-Row Anomeric Interactions The Reverse Anomeric Effect The Kinetic Anomeric Effect Applications of the Anomeric Effect in Organic Synthesis

Abstract: A series of 1-N-iminosugars were synthesized to supply the need for glycosidase inhibitors that are both highly potent and selective for β-glycosidases. Designed on the basis of the transition-state model of the β-glucosidase reaction, these iminosugar inhibitors differ from the currently available inhibitors in possessing a nitrogen atom at the anomeric position of the pyranose ring, thereby generating a positive charge on the anomeric position rather than on the ring oxygen of the sugar. Their syntheses, starting with a readily available carbohydrate derivative, involve (i) introduction of an amino functionality as an azido group, (ii) formation of a 1-N-iminopyranose ring with reductive amination, and (iii) stereoselective introduction of a hydroxymethyl or methyl group and were accomplished in a highly stereoselective and efficient manner. The inhibitory potencies of the 1-N-iminosugars were evaluated against several α- and β-glycosidases, and they were found to be extremely potent and highly specific...