Glycoside hydrolysis acetamido groups

D. Piszkiewicz and T. C. Bruise, Glycoside hydrolysis. I. Acetamido and hydroxyl group catalysis in glycoside hydrolysis, J. Am. Chem. Soc., 89 (1967) 6237-6243. 

Methylation of methyl 2-acetamido-4,6-0-benzylidene-2-deoxy-a-D-altroside, obtained by hydrolysis of the 3-acetate estergave a 3-methyl ether. Hydrolysis of the benzylidene group, and tritylation of the resulting glycoside, led to crystalline derivatives. 

Deacetylation. N-Acetyl groups of acetamido desoxysugars are selectively cleaved under mild conditions by treatment with triethyloxonium fluoroborate, followed by hydrolysis of the intermediate O-ethyl acetamidium fluoroborate.11 Ester, acetal, and glycosidic linkages are not affected. 

The syntheses of glycosides and esters of daunosamine (3-amino-2,3,6-trideoxy-L-/yxo-hexose) suitable for use in the synthesis of analogues of dauno-mycin and daunosamine-containing oligosaccharides have been reported. Methyl (methyl 3-acetamido-2,3-dideoxy-a-D- fe< -hexopyranosid)uronate (6) has been described in which the carboxylate grouping was established from the corresponding 6-azide by sequential photolysis, mild hydrolysis, and oxidation of the 6-aldehydo group. 

The fortuitous hydrolysis of the ester of 2 in the refluxing aqueous acetone was somewhat surprising since a previous report of the reaction employing the related a-methyl glycoside of 2 (methyl-a-(methyl-5-acetamido-9-tosyl-3,5-dideoxy-D-g(> ccro-D-ga/acro-2-nonulopyranosid)onate (6), resulted in the retention of Ae methyl ester (Scheme 2). To confirm the different stability of the meAyl ester of the two compounds, 6 was synthesized and heated under reflux with sodium azide in aqueous acetone under identical conditions to that used for 2. As previously noted, no hydrolysis of the methyl ester was observed. Given the different reaction patterns of 2 and 6, the existence of free C-2 hydroxyl group of 2 facilitates the hydrolysis. 

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