Abstract
Publisher Summary This chapter discusses cyclic monosaccharides having nitrogen or sulfur in the ring. Free monosaccharides are generally not acyclic, carbonyl structures, but occur as cyclic hemi-acetal forms in which the carbonyl group has reacted with a hydroxyl group of the same molecule; for example, for an aldopentose, it reacts with the C-5 hydroxyl group to form a pyranose ring or with the C-4 hydroxyl group to give a furanose ring. The 5-amino-5-deoxy-D-glucose found in the antibiotic nojirimycin is the first known natural sugar having nitrogen in the hemi-acetal ring. The thiol group exhibits the greatest tendency to form a hemiacetal, and this tendency exceeds that of the amino group. The unsubstituted amino group shows reactivity higher than that of the hydroxyl group; this is shown by the ease with which aldoses form glycosylamines. The nucleophilicity of the acylamido group is distinctly weakened by amide mesomerism, and, accordingly, this group shows reactivity much lower than that of a hydroxyl group.
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