Isosaccharinic acid degradation

Lactulose is unstable in alkaline solution, degrading by alkaline peeling and /3-elimination reactions to yield galactose, isosaccharinic acids, and other acid products (Corbett and Kenner 1954). Amines can bring about dehydration and degradation reactions (Hough et al. 1953). Lactulose is similar to sucrose in humectant properties (Huhtanen et al. 1980). 

The five-carbon isosaccharinic acid, 3-deoxy-2-C-(hydroxymethyl)-DL-glycero-tetronic acid, was obtained from alkali-degraded oligo- and polysaccharides containing fi-( —> 4)-linked D-xylose residues.301... 

It has long been known that D-glucose substituted at C4, as in the disaccharides lactose, cellobiose, and maltose (see page 48), is particularly suitable for the preparation of a -D-isosaccharinic acid through treatment with lime-water. Since this acid is only a minor product of the action of alkali on unsubstituted D-glucose, the presence of a substituent at C4 must preferentially direct the alkaline degradation to the isosaccharinic structure. 

Figure 9.3 Mechanism of the formation of isosaccharinic acid and metasaccharinic acid during alkaline cellulose degradation.

In a reinvestigation of the Duff degradation, treatment of the calcium salt of D-isosaccharinic acid with H2O2 and Fe salts gave rise to 3-deoxy-D-g/ycero-pent-2>ulose. l Some carboxyl-reduced derivatives of Kdo (3-deoxyketoses) ate mentioned in Chapter 3, and some 2,6-and 3,6-dideoxy-6-fluorosugars are discussed in Chapter 8. 

Deoxy-D-glycero-hexo-2,3-diulose is a typical product of degradation and 4-0-substituted derivatives of fructose (e.g. lactulose, which arises by isomerisation of lactose). 1,2-Enolisation of 4-deoxy-D-g lycero-hexo-2,3-diulose yields, via the appropriate l-ene-l,2-diol, unstable 4-deoxyhexos-3-ulose, which splits into formic acid and 1,2-enediol of 3-deoxy-D-glycero-pentulose in neutral or alkaline solutions by a reverse Claisen condensation mechanism. This sugar can be oxidised to 3-deoxy-D-glycero-pentos-2-ulose or may dehydrate to form 3,4-dideoxypentosulose (Figure 4.32). Other reaction products are isosaccharinic acids. 

Earlier investigators of the alkaline-degradation products of lactose found succinic acid, formic acid, and a crystalline lactone, later identified by Kiliani as a -D-isosaccharinic lactone. This lactone was obtained in about 20% yield from the action of lime-water on lactose also detected as products of this reaction were D-galactose, lactic acid, pyruvaldehyde, formaldehyde, and other saccharinic acids. The... 

Alkaline degradation of cellulose is important during alkaline pulping it produces non-volatile acids > which are, for the most part, D-gluco-isosaccharinates. " ... 

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