BEHAVIOR OF GLYCOSIDIC LINKAGES TO OXYGEN-ALKALI

Abstract

The behavior of glycosidic linkages to the oxygen-alkali treatment has been studied, using low molecular compounds. This treatment of cellobiitol yielded many kinds of acids (Fig.1) together with glucitol which was only one neutral product. These acids, except 3-deoxy-pentonic acid (VII) and 3, 4-dihydroxybutyric acid (VIII), were also formed from glucose by the same treatment. This result suggests that glucose may be a precursor of the acids other than the acids (VII) and (VIII), although it was not detected among the degradation products owing to its low stability under the severe alkaline conditions adopted. The formation of the acids (VII) and (VIII), and glucose from cellobiitol may be explained by the scheme shown in Fig.2. A scheme in which hydroxyl radical is involved in the cleavage of glycosidic linkages (Fig.3) was expected, but found not to be important, if any, because the yield of gluconic acid was lower than that of mannonic acid. The formation of glucitol from cellobiitol can be explained by the scheme in Fig.4, but the cyclic acid (XII) which should be formed according to this scheme could not be detected.The oxygen-alkali treatment of methyl 4-O-methyl-β-_??_-glucopyranoside yielded only three kinds of acids. They were separated gas-liquid chromatographically as TMS derivatives (Fig.5) and identified as glyceric acid, methyl 2-carboxy-3-deoxy-β-D-pentofuranoside (XIV) and methyl 2-carboxy-3-O-methyl-β-D-pentofuranoside (XVII) by the use of a mass spectrometer (Fig.6).Methyl β-D-glucopyranoside has the same stability to oxygen-alkali as methyl β-D-xylopyranoside, though the former contains an extra primary hydroxyl group (Table 1).