Pentose, and pentitol

There are various, interrelated reasons why the abilities of yeasts to utilize pentoses and alditols should be associated. (i) Pentoses and pentitols may be reversibly interconverted by dehydrogenases (it) catabolic routes may be shared and (Hi) many of the alditol dehydrogenases have particularly wide substrate-specificity, so that a single enzyme may act on pentitols and pentoses, as well as on hexi-tols and hexoses. 

Physiology and Clinical Uses of Pentoses and Pentitols, B, L, Horecker et al, Eds. (Springer-Verlag New York, 1969) 408 pp Sugars in Nutrition, H, L, Sipple, K, W. McNutt, Eds. (Academic Press, New York, 1974) passim G, E, Demetra-kopoulos. H. Amos. World Rev Nutr Diet 32, 96-122 (1978) R, Ylikahri Adv, Food Res. 25, 159-180 (1979). Book XylitoL 3 N. Counsel, Ed. (Applied Science London 1978) 191 pp. 

The furoisoxazoline (8) has been used for the total synthesis of amino-deoxy pentose and pentitol derivatives, synthesis of the latter being outlined in Scheme 5. ... 

Conversion of pentoses and pentitols (From Jansen and Tsao (1983), with permission)... 

Very little work on the synthesis of pentitols had been carried out before 1928. Those pentitols which had been synthesized were made by the reduction of pentoses. Several pentitol intermediates had been synthesized" and it seemed desirable to attempt to complete the synthesis of pentitols from the unsaturated intermediates, using the methods which had been successfully employed in the synthesis of hexitols. 

Manganese(III) has been employed for the oxidation of aldoses, and a general mechanism for the oxidation has been proposed.167 The oxidation of hexoses, pentoses, hexitols, and pentitols by Mn(III), as well as by other cations, was proposed to proceed via a free-radical mechanism,168 as shown in Scheme 26. Oxidation of alditols produces the corresponding aldoses, which are further oxidized in the presence of an excess of oxidant to the lower monosaccharides and thence to formaldehyde, formic acid, and even carbon dioxide. The kinetics for the oxidation of aldoses and ketoses by Mn(III) in sulfuric acid medium have been reported.169... 

The kinetics of the oxidation of hexoses, pentoses, hexitols and pentitols by vanadium(V, cerium(IV), manganese(III) and thallium-(III) in aqueous acidic media have been claimed to proceed via a... 

The pentose sugars, ribose and xylose also yield the pentitols on reduction under similar conditions [29]. In these cases a by-product is the 2-deoxypolyol formed by reductive elimination of the hydroxyl group adjacent to the carbonyl function. This reaction predominates during the reduction of D-xylose in solution at pH 9 at amalgamated lead when 2-deoxy-D-xylitol (III) is formed in 62% yield [30]. 

FIG. 10. —Possible Routes of Pentitol and Pentose Catabolism by Yeasts (after Barnett903). 

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