Sugar Alcohols

Abstract

The sugar alcohols are, as their name implies, those compounds obtained when the aldo or keto group of a sugar is reduced to the corresponding hydroxy group. As such, they are alcohols. Sugars are, of course, themselves polyhydroxy compounds, and so the corresponding sugar alcohols merely have one more alcohol grouping --- hence alternative names for the group are polyols, polyalcohols, or polyhydric alcohols. Actually the term ``polyol'' could properly cover a much larger group containing any compound with three or more hydroxy groups, but common usage normally restricts the term to those compounds closely related to sugars and sugar derivatives. Even limited thus, the polyols form a broad group, containing both the straight-chain or acyclic polyols (glycitols), which are our sugar alcohols, and the cyclic polyols (cyclitols) such as inositol, covered in Chapter 6, this Volume. Chemically, physically, and biologically the sugar alcohols closely resemble the sugars to the extent that some are even sweet to the taste and one (xylitol) is being tested as a food sweetener. In the plant they are almost always closely related, in their biogenesis and metabolism, to the companion sugar (usually the ketose): in many organisms, particularly the fungi, they replace the sugars in many of their functions. It has therefore been convenient sometimes to regard them as special kinds of sugar in their metabolic roles, and to some degree that is the view I will take here.