Furanosides hydrolysis

Partial hydrolysis of dithioacetals has been found useful for the preparation of anomers, not obtained by the methods discussed above, and furanosidic thioglycosides [37,45]. 

Fischer was intrigued by the fact that emulsin caused hydrolysis of both / -glucosides and / -galactosides but had no effect on either the a- or / -xylo-sides (33). Since, at the time, Fischer expected glycosides to be furanosides, he suggested that both the enzymes required the presence of a free hydroxyl group at position 5 of a hexoside. 

Special examples of stable glycofuranosides will be discussed in Section VI, 4, but mention may be made here of two distinctive glycofuranosides. Ballou and Fischer 0 refluxed di-O-isopropylidene-D-monno-hexodialdose in methanolic hydrogen chloride, and obtained a 20% yield of a compound containing two furanoside rings, namely, the dimethyl , a-difuranoside of D-manno-hexodialdose. It was identified by methylation, by its strong dextrorotation, and by its rate of hydrolysis by 0.01 N hydrochloric acid. 

The lower rates of hydrolysis (see Table IX) found for 1-thio-D-gluco-furanosides are attributable to the lower basicity of the sulfur atom,141 and thus, less protonation of the 1-thio-D-glucoside occurs in acid solution, in comparison to the D-glucofuranosides. 

Complete hydrolysis of the polyglycoses gave the starting monomer. Hydrolysis with dilute acid gave an initial rise in optical rotation which was attributed to the hydrolysis of furanosidic bonds. The positive rotations suggest the presence of o-d as well as of 0-D-glycosidic linkages. The isolation... 

Obayashi and Schlosser [43] have briefly described syntheses of erythro-sphingo-sine and threo-sphingosine from D-mannose and D-ribono-1,4-lactone, respectively. For the synthesis of ery/Aro-sphingosine (35) D-mannose was converted into benzyl 2,3 5,6-di-O-isopropylidene-manno-furanosides and hydrolysis of the 5,6-0-iso-propylidene group followed by periodate oxidation and borohydride reduction and protection gave the methoxymethyl ether (28). This was converted into the chloride... 

IV. Effect of the 1,6-Anhydro Ring on the Rate of Acid Hydrolysis of the Furanoside Structure of 1,6-Anhydrohexofuranoses... 

The two hexosans D-glucosan < l,4>/9< 1,6> and D-galactosan-<1,4>o<1,6> are 1,6-anhydrides of the furanose forms of the sugars and may be looked upon as internal hexofuranosides. In view of the generally more rapid acid hydrolysis of furanosides, such as methyl D-glucofuranoside or sucrose, as compared with normal pyranosides, the behavior of these hexosans toward acid hydrolysis is noteworthy. 

Phosphorylation of XLVII with phosphorus oxychloride in pyridine solution, followed by hydrolysis to remove the methyl and isopropylidene residues, gave D-ribose 5-phosphate (XLVIII) which, as its barium salt, was found to be identical with the barium salt of the D-ribose phosphate from inosinic acid. By way of further confirmation of the structure of D-ribose 5-phosphate, Levene, Harris and Stiller129 showed that in methanolic hydrogen chloride solution both the natural and synthetic material mutarotated in a manner characteristic of a sugar which can form only a furanoside. 

The required olefin alcohols were prepared via a slight adaptation of the literature protocols (9). Kinetic furanoside formation was followed by benzylation (10a —> 11a) and hydrolysis produced the lactols 12a that were subsequently purified by column chromatography. Wittig olefination then... 

The rate of hydrolysis of polysaccharides is affected by several factors. Because of substituent interaction effects, furanosides are hydrolyzed much more rapidly than the pyranoside analogues. Differences in the hydrolysis rates of diastereomeric glycosides are significant. For example, the relative hydrolysis rates of methyl-a-D-gluco-, manno-, and galactopyranosides are 1.0 2.9 5.0. This can be related to the stabilities of the respective conjugate acids, which are transformed into the half-chair carbonium ions at different rates. Also, substituents bound to the C-2 position obviously prevent the formation of the half-chair conformation. 

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