Hydroxylamine sugar oximes

The sugar oximes needed for degradation by Wohl s method are best obtained by using hydroxylamine hydrochloride and pyridine.946... 

The sugars, probably in the free-aldehyde form (I), react 248) with hydroxylamine to give the sugar oximes (II or III) ... 

The hydrazone formed in this reaction usually crystallizes easily and is only sparingly soluble. A variation of this reaction is used in the chemistry of sugars. Oximes are formed analogously with hydroxylamine. 

Formyl C-glycosides, prepared in three steps via the thiazole-based formy-lation of sugar lactones are readily condensed with hydroxylamine to give the corresponding oximes. The latter are the precursors of glycosyl nitrile oxides via the N-bromosuccinimide method (41). 

Another synthetic approach for generating sugar-containing nitrones is by initial treatment of sugars with unsubstituted hydroxylamine. The resulting cyclic hydroxylamine of the tautomeric mixture (68a) and of the open chain oxime (68b) react with aldehydes to give the corresponding nitrones (69) (Scheme 2.24) (216-220). 

Partially methylated, acetylated aldononitriles are acyclic derivatives readily formed from reducing sugars by reaction with hydroxylamine in pyridine, followed by the addition of acetic anhydride to effect elimination of acetic acid from oxime acetates and acetylation of unsubstituted hydroxyl groups. These derivatives, although less extensively used, appear to give good GLC separations, and their mass spectra can be readily interpreted without the problem of structural symmetry (75MI3). 

The aldehyde group of an aldose reacts with such carbonyl reagents as hydroxylamine and phenylhydrazine (Section 16.8B). With hydroxylamine, the product is the expected oxime. With enough phenylhydrazine, however, three molar equivalents of phenylhydrazine are consumed and a second phenylhydrazone group is introduced at C2. The product is called a phenylosazone. Phenylosazones crystallize readily (unlike sugars) and are useful derivatives for identifying sugars. 

Various mononitrones, e.g. (41), and symmetrical and unsymmetrical dinitnmes, e.g. (42) and (43), respectively, have been synthesized. The dinioones could be reduced to their corresponding bis-(A(-hydroximino)-derivatives. Such sugar hydroxylamines are precursOTS free radicals, these being formed on contact with air or by oxidation with lead dioxide, and able to be observed by e.sx spectroscopy. In the case of the bis(A/-hydroximino)-derivatives, only mono-radical species were observed, any di-radicals being present in concentrations insufficient for detection. The nitrones (44) and (45) were obtained on condensation of the oximes of protected 2-acetamino-2,4-dideoxy-D JO /t>-hexose and hexuronate derivatives with 4-methoxybenzaldehyde. ... 

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