Saccharide osazones

The structure of inosose bis(phenylhydrazones) resembles that of saccharide osazones in that the bishydrazone residues in both are chelated that is, bridged by an imino group (the other NH group is unchelated). 

The infrared spectra of phenylosazones have also been studied in detail, and have been suggested as a means of identification of the different saccharide osazones. Saccharide osazones show the characteristic hydroxyl bands at 3 n, the C=N band of the hydrazone residues at 6.3 n, and three bands attributed to the phenyl ring. In the case of acetylated osazones, the 0-acetyl band appears at 1735 cm. and JV-acetylated derivatives show the A-acetyl band at " about 1640 cm.. These characteristics have greatly simplified the differentiation of 0-acetyl from iV-acetyl groups in acetylated osazones. Also, for benzoylated osazones, the differentiation offers no difficulty the 0-benzoyl band appears at 1725 cm. and the A-benzoyl band at 1685 cm.. ... 

The hydrazine derivatives of saccharide are here discussed in sections on saccharide azines, which are formed when one hydrazine molecule reacts with two saccharide molecules saccharide hydrazones and glycosylhy-drazines, which are the tautomeric acyclic and cyclic products formed when one hydrazine molecule reacts with one sugar residue saccharide osazones and poly(hydrazones), which are formed when two or more hydrazine molecules are linked to a saccharide residue and, finaly, hydrazones of carba-sugars and related compounds. 

It should be noted that the members of the chelated pair have never been separated in the case of saccharide osazones, but this has been achieved with noncarbohydrate bis(phenylhydrazones). In at least one case they were found to be interconvertible, either by irradiation with light (pho-tochromism) or by treatment with acids or bases (see Fig. 2)316... 

Saccharide osazones (183) are relatively stable in cold concentrated alkalies. but degrade progressively with time. The degradation starts at the... 

Formation of Pyrazoles from Bis(hydrazones).—Mesoxaldehyde bis(phenylhydrazone) (193), obtained by periodate oxidation of saccharide osazones (192) is readily cyclized in the presence of acids to give l-phenyl-4-phenylazo-pyrazole (195).162 365 Hexulose phenylosazones (192) are also disproportionaled in the presence of acidic salts of carbonyl reagents, such as hydroxylamine hydrochloride, to give l-phenyl-4-phenylazo-pyrazolin-5-one (196). The reaction probably proceeds via mesoxalic acid 1,2-bis(phenylhydrazone) (194).365 The hydroxalkyl derivatives of 196 are produced from dehydroascorbic acid bis(phenylhydrazone) by treatment with base to open the lactone ring and permit the conversion of 197 to 199.351,366 Another type of pyrazole that is formed by dehydrating osazones with acetic anhydride is discussed later under anhydroosazones (see Schemes 45,53). 

The saccharide derivatives best suited for cyclization to pyrazolines and pyrazoles are the hydrazones and osazones, which possess the two adjacent nitrogen atoms required. 

The chemistry of carba sugars is quite similar to that of cyclitols both groups lack the latent carbonyl groups of their saccharide counterparts, and therefore fail to exhibit many of the characteristic properties of monosaccharides. Thus carba sugars and cyclitols do not form hydrazones or osazones, nor do they mutarotate, or reduce heavy-metal salts in base, in contrast to their oxidation products, the inososes. 

Fischer s formulation of phenylosazones in the acyclic structure, such as (43), was based on the fact that the same osazone is produced from two epimeric aldoses and the corresponding 2-ketose, as well as from their phenylhydrazones, indicating that, in the osazone, the phenyl-hydrazine residues are attached at C-1 and C-2 of the saccharide chain. As the asymmetry at C-2 is destroyed during the reaction, it is found that, for a given substituted hydrazine, there are eight isomeric hexose osazones (four D and four l isomers) and four pentose osazones (two d and two l). 

The Fiesers suggested, on theoretical grounds, that osazones exist in tautomeric, chelated forms which stabilize these unsaturated compounds and prevent the reaction of hydrazines with saccharides from proceeding... 

The reactions discussed in this Section are those involving the removal of the elements of water from osazones, and not merely the preparation of osazones from anhydro saccharides. There are, at present, three tjT>es of anhydro-osazone and, in all three types, the elements of water are eliminated from the hydroxyl group at C-3 and another group of the osazone, accompanied in some cases by inversion of configuration at C-3. 

Because of the chelated structure of sugar osazones, the osazone formazan 181, obtained by coupling diazotized [14C]aniline to a saccharide phenylosazone (180) loses 42%) of the label (as aniline) upon conversion to an osolriazole (182), whereas the formazan of an unchelated osazone, such as pyruvaldehyde osazone loses exactly half of the radioactivity as aniline during osolriazole formation (Scheme 40).168... 

Another important value of the osazone-based approach is its utility in preparation of other ketosamines. Phenylosazones of many mono- and di-saccharides are readily prepared in high yields as pure crystalline materials from both aldoses and ketoses, and such kctosamincs as 1-amino-1-deoxy-L-sorbose, for example, can be synthesized most rationally from commercially available L-sorbose. ... 

When osazones are used as derivatives for identification it should be borne in mind that saccharides differing in configurations only at the last two carbon atoms afford identical osazones (for example, D-glucose, D-mannose, D-fructose). 

---