Schiff bases glycosylamines

This is the mechanism that was proposed originally by Kuhn and Wey-gand. The nitrogen of the iV-substituted glycosylamine (VI, R = H or a radical) accepts a proton from the acid catalyst, to form the ammonium ion (VII) which presumably is in equilibrium with the cation of the Schiff base (VIII). IsbelP then explains the shift of the double bond on the basis... 

The open-chain forms of glycosylamines (see Section 1.2.3) are Schiff bases and are labilised towards deprotonation of an adjacent carbon in much the same way as the open-chain forms of the sugars themselves. Reprotonation of the first-formed enamine on the carbon bearing the nitrogen atom will give an a-aminocarbonyl compound. The formation of a l-deoxy-l-amino-2-ketoses... 

Aldehyde Amine carbohydrates Aldehyde-amine Schiff base or glycosylamine... 

The crystal structures of four mannose-derivatives which might exist as either open-chain Schiffs bases or as glycosylamines showed that the hydroxylamine derivative is the oxime 34, whereas the semicarbazide, aniline- and p-chloroani-line-derivatives are the p-glycosylamines 35. ... 

When the reaction was first applied to the sugars, amorphous products were obtained which were considered to have the Schiff base structure. By heating glucose or fructose in an alcoholic solution of aniline, Sorokin 10) was able to prepare crystalline products, although the crystallinity of iV-phenyl-D-glucosylamine is in doubt 10, 11). Many other crystalline glycosylamines are known at present in the aliphatic 5, 12) and aromatic 13,14) series of amines. 

Many glycosylamines exhibit mutarotation which may be due to the establishment of an equilibrium between the a- and jS-isomers and the corresponding Schiff base or possibly to a partial hydrolysis (id, 62 dP, Pa,6). The mechanism outlined necessitates the presence of a hydrogen atom attached to the nitrogen atom, i.e., the aglycon amine must be a primary amine. However, the observed mutarotation of the corresponding derivatives of secondary amines may be ascribed to the formation of an intermediate quaternary ion R2N+=CH—(CHOH)4—CH2OH. 

PhenyIethylamine has been resolved following conversion into diastereoiso-meric glycosylamines by reaction with 1,2,3,4,6-penta-O-acetyl-D-glucopyranose. iV-Ribofuranosyl derivatives of nitrogen-containing heterocyclic compounds are referred to in Chapter 21, and the conversion of Schiff-base derivatives of aldehydo-sugais into 1-aminophosphonates is noted in Chapter 18. 

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