Formation of the Nitrogenated Derivatives

The formation10 12 of N-acetyl-a-D-glucofuranosylamine (15) from 1,2,3,4,6-penta-O-acetyl-D-glucopyranose, and, by extension, of other N-acyl-D-glycosylamines, would start with the rapid elimination of the acetyl group on 0-1 to give 89. In this way, C-l is ready to combine with ammonia to give the intermediate 90 and, subsequently, the 

Further experiments disproved Wohl s theories1-3 4 as to a direct condensation mechanism. By degradation of 2,3,4,5-tetra-O-acetyl-L-arabinononitrile82 (5) in the presence of propionamide or benzamide, l,l-bis(acetamido)-l-deoxy-L-erythritol (6) was obtained in yields comparable to those obtained when the reaction was conducted in the absence of these extraneous amides. Also, an excess of acetamide in the medium did not increase the formation of nitrogenated carbohydrate derivatives. 

Compound 5 (see p. 82) was allowed to react83 with ethanolic ammonia-15N in the presence of an excess of acetamide-14N, and compound 6 containing a percentage of 15N similar to that of the ammonia employed was obtained, showing that, actually, the reaction occurs by an intramolecular mechanism. Were the mechanism intermolecular, in accordance with Wohl s views, the percentage of 15N in 6 would have been lower. Likewise, ammonolysis of D-glucose pentabenzo- 

An alternative to the mechanism of Isbell and Frush was proposed by Deulofeu and coworkers.22 The initial stage of the reaction would be similar in the formation of the aminol precursor 94. This intermediate would be in resonance with an immonium ion 95 that, after acetyl migration, would afford 97. Nucleophilic attack by ammonia on C-l of this intermediate would give 98, and, finally, the 1,1-bis-(acylamido)-l-deoxyalditol (100), after migration of another acyl group as depicted in 99, 

The results, shown in Table I, provided evidence that, for cyclic benzoates, there is a great contribution of the benzoyl groups on 0-3 and 0-4, an intermediate contribution by that on 0-6, and a small contribution by the benzoyl group on 0-2, whereas that on 0-1 does not contribute at all to the formation of the l,l-bis(benzamido)-l-deoxyalditol. 

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