Osones structure

XXII, for which they proposed the alternative name 1-phenyl-D-fructo-sone reaction with o-phenylenediamine produced a crystalline compound to which they assigned the structure XXIV, that is, 2-(D-orobwo-tetrahy-droxybutyl)-3-pheuylquinoxaline, the substituted osone reacting in the open-chain form XXIII. Compound XXIV, on treatment with phenylhy-drazine, yielded crystalline 2-formyl-3-phenylquinoxaline phenylhydrazone... 

XXV). No evidence was presented by Ohle and his colleagues to support the formulation of these derivatives with a free carbonyl group, and further investigation of their structure and properties is desirable before relating them to the free osones. 

D-Galactosido-D-glucosone and D-glucosido-D-galactosone were prepared by Fischer and Armstrong203 by the action of benzaldehyde on the osazones of synthetic disaccharides. Both osones were hydrolyzed by emulsin. There is some doubt as to the precise structure of the parent sugars.206... 

The two chief structural types which have to be considered are (a) those with a single lactol ring and a free or hydrated carbonyl group and (b) those in which two lactol rings are present. There is at present no conclusive evidence that either type of structure is the main component of D-glucosone in solution. Glycoside formation does not proceed normally in the osones,... 

In the previous paragraph, the products of the mild hydrolysis of dichlorides prepared from the 2-hydroxyglycals were termed osone hydrates. The osone hydrate structure VI is that expected on the basis of structure V for the dichloride. The correctness of the assigned structure seems to be established beyond question by the analyses, properties, and reactions of the members of this family of compounds. Efforts to obtain the unacyl-ated parent substances have resulted only in yellow sirupy materials. 

Natural sialic acids (Schauer 1982 1991) are derivatives of 5-amino-3,5-dideoxy- D-glycero-D-galacto-nonu osonic acid 12.1. This awkward name has been replaced by neuraminic acid . The most common derivative is N-acetyl-neuraminic acid 12.2 whose configuration is easy to memorize because, in the Fischer representation, 12.3, it is presented as an aldolic condensation product of N-acetylmannosamine (2-acetamido-2-deoxy-D-mannose) and pyruvic acid. When the expression sialic acid is used without any other precision, it is in reference to derivative 12.2. It exists in the free state or glycosidated in the d-conformation, which allows an equatorial disposition of the three-carbon side chain. Structure 12.2 represents the stable /3-anomer of the free sugar with an axial anomeric hydroxyl group and all-equatorial non-anomeric substituents. An X-ray spectrum of this crystallized /3- anomer confirms this conformation and reveals, moreover, that the side chain has the zig-zag conformation with two... 

Osazones, phenyl-, of sugars, 139 mutarotation of, 144 structure of, 129 Osones, deoxy-, 73, 74, 76 Oxidation,... 

Compounds of this class are characterized by their instability in acidic solutions, in which hydrolysis of the enolic ether grouping is followed by an elimination, to give unsaturated, osone derivatives, namely, 3,4-dideoxy-D-j(lj/cero-hex-3-enos-2-ulose (85, R = H) and its 6-methyl ether (85, R = Me), which are unstable, undergo ring contraction, and lose the elements of water to give, ultimately, 5-(hydroxymethyl)- and 5-(raethoxy-methyl)-2-furaldehyde (86, R = H or Me). For the monomethyl ether (84, R = H), this decomposition is complicated by a side reaction probably involving the formation of 3,6-anhydro structures. 

Lactose forms a phenylhydrazone, osazone, and osone. The composition of these substances indicates that lactose contains one free carbonyl group. It is an anhydride of dextrose and galactose, in which one carbonyl group is involved in the union of the molecules, and one is free. The structure of the products formed on oxidizing lactose indicates that the free carbonyl group is in that part of the molecule which yields dextrose on hydrolysis. 

A method of considerable historical interest is the transformation of the aldoses to the ketoses through the osazohes and osones (247). In his classical work which led to the synthesis of the isomeric sugars, Fischer utilized this procedure. Although better preparative methods are now available, the method still is important for demonstrating structural relationships. The... 

Formula 4.59 shows examples of products obtained on the decomposition of 3-deoxy-osones. The best known compounds are 5-hydroxymethylfurfural from hexoses (HMF, II in Formula 4.59) and furfural from pentoses (I in Formula 4.59). Taking the furanoid structures of 3-deoxyosone as a basis (Formula 4.55), 3,4-dideoxyosone is obtained after ring opening, enolization, and water elimination (Formula 4.60). Water elimination from the hemiacetal form of 3,4-dideoxyosone directly yields HMF. Taking into account the water elimination required to form 3-deoxyosone (cf. Formula 4.55), 5-hydroxymethylfurfural is formed from hexose by the stoichiometric elimination of 3 mols of water. 

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