Showing papers in "Advances in carbohydrate chemistry in 1955"

The Amadori Rearrangement

Abstract: Publisher Summary This chapter discusses the reaction that is the isomerization of an aldosylamine to a 1-amino-1-deoxy-2-ketose. This rearrangement was named after Amadori by Kuhn and Weygand, for Amadori was the first to demonstrate that condensation of D-glucose with an aromatic amine ( p -phenetidine, p -anisidine, or p -toluidine) would yield, according to experimental conditions, two structurally different isomers, which are not members of an α, β anomeric pair. Amadori did not realize that an isomerization (“rearrangement”) from an aldose to a ketose configuration had occurred. However, he did discern (by change of optical rotation in acid solution) that one isomer is much more labile than the other toward hydrolysis and more susceptible to decomposition on standing in the solid state in air. He recognized correctly that the labile isomer is the N -substituted glucosylamine, but he mistakenly thought that the stable isomer was a compound of the Schiff-base type. Authentic crystalline products of the Amadori rearrangement have so far been obtained only from D-glucose, D-mannose, and 5- O -trityl-D-xylose as the sugar components. Occurrence of the rearrangement (or at least 1, 2-enolization of the N -substituted glycosylamine) was demonstrated indirectly, however, by isolation and characterization of crystalline epimeric hydrogenation products derived from D- and L-arabinose and also from D-xylose.

The stereochemistry of cyclic derivatives of carbohydrates.

Abstract: Publisher Summary This chapter presents a comparison between carbohydrates and analogous alicyclic compounds, with emphasis on the stereochemistry of the ring systems involved. Carbohydrate chemistry is especially rich in examples of ring structures formed by reversible reactions, such as glycosides and cyclic acetals, and provides a more convenient field for examining the factors governing the stability of rings than does alicyclic chemistry, in which ring closures are usually irreversible. The prominent reversible reactions of carbohydrates are nearly all catalyzed by acids, whereas the equilibria most studied in alicyclic chemistry, such as epimerization of secondary hydroxyl group and of ring junctions, are base-catalyzed. Epimerizations at α positions in aldonic acids and 2,4:3,5-di- O -methylenehexaric acids are well established, but base-catalyzed epimerization of secondary hydroxyl groups in the rings of glycosides and anhydro derivatives does not seem to have been investigated.

The glycosyl halides and their derivatives.

Abstract: Publisher Summary This chapter discusses that the glycosyl halides are compounds in which the hydroxyl group at the reducing carbon atom of a sugar is replaced by halogen. As such, the glycosyl halides are rare, only a few fluorides being well authenticated. However, the fully acylated glycosyl halides, particularly the acetylated compounds, sometimes referred to as “acetohalogeno sugars” or “acetohalogenoses”, are very well known. The most familiar of these is 2,3,4,6-tetra-O-acetyl-α-D-glucosyl bromide (“acetobromo-α-D-glucose”). The poly-O-acyl derivatives of the glycosyl halides are among the most important intermediates for synthesis in carbohydrate chemistry; moreover, their chemistry has considerable intrinsic interest. Most of the methods for the preparation of glycosyl halide derivatives depend on the replacement by halogen of an acyloxyl (nearly always acetoxyl) group a t the reducing carbon atom. Hence, the methods for the synthesis of a large number of the glycosyl halide derivatives can be exemplified by description of those used for converting fully acetylated sugars into O-acetylglycosyl halides. As might be expected, treatment for prolonged periods often results in replacement of a second acetoxyl group. Other methods available for the synthesis of glycosyl halide derivatives involve the replacement of hydroxyl and alkoxyl by halogen, the opening of anhydro rings with hydrogen halides or equivalent reagents, and the addition of halogen or hydrogen halide to certain unsaturated sugar derivatives. Glycosyl iodide derivatives are usually prepared from the corresponding bromides by reaction with sodium iodide.

The chemistry of heparin.

Abstract: Publisher Summary This chapter presents an account of the more recent developments in the chemistry of heparin together with the significant features of the earlier work. Heparin, the blood anticoagulant present in circulatory tissue is now recognized to be an important and chemically unique polysaccharide of considerable biological significance. To ascertain the origin of its blood-coagulating properties, crude cephalin was submitted to a careful fractionation. Fractions were obtained which unexpectedly inhibited the coagulation of oxalated, dog serum. This was a significant discovery because no anticoagulant had previously been found in mammalian tissue. Because of its abundance in liver, the anticoagulant material was named “heparin.” In addition to its role in the blood-coagulation process, heparin shows other types of biological activity, such as its action in clearing fat globules from the blood stream (alimentary lipemia) and its use in the treatment of frost-bite. Heparin also possesses activity toward certain strains of bacteria; for example, in a protein-free medium, heparin was found to be bacteriostatic toward Micrococcus pyogenes at 100 p.p.m.

Column chromatography of sugars and their derivatives.

Abstract: Publisher Summary This chapter discusses the column chromatography of sugars and their derivatives. Column Chromatography is a specialized manipulation of the general technique of selective adsorption with powdered materials. These adsorbents are molded vertically in the shape of cylindrical columns. Three techniques are usually employed in the formation of such chromatographic columns: dusting dry powder into an empty dry tube, slowly adding dry adsorbent to a tube containing liquid, and pouring thin slurry of adsorbent and developer into an empty tube. The sensitivity and flexibility of the chromatographic method are improved markedly by allowing the sugars and developers to pass, under pressure, down through the adsorbent into a very small cuvette, which is connected to a fraction collector outside the temperature-controlled bath. The cuvette is aligned with a sensitive interferometer, which permitted rapid recognition of composition changes in the effluent. The effluent turnover was quick in this small cell; thus, the opportunity for the intermixing of zones was greatly reduced. The combination of this excellent method together with an established scale of certain sugars in the order of their increasing affinity to carbon provided a powerful tool for the resolution of sugar mixtures.

Polysaccharides Associated with Wood Cellulose

Abstract: Publisher Summary This chapter discusses the polysaccharides associated with wood cellulose Preparations of wood cellulose generally have a higher carboxyl-group content than has linters cellulose, and some of these carboxyl groups are believed to be present either as polyuronides or as occasional uronic anhydride moieties ill the cellulose chain or in associated polysaccharides In certain preparations of cellulose, minor amounts of araban and galactan have been detected Neither in wood nor in any wood cellulose preparation has it been established that the polysaccharides are homogeneous The polysaccharides associated with cellulose in wood, or wood pulps, are often referred to as “polyoses” Physicochemical methods of analysis that yield information concerning degree of polymerization (DP), chain-length distribution, and accessibility of wood cellulose have been brought to a high degree of precision and have proved their value Chromatographic methods are now yielding detailed information regarding the organic chemistry of wood cellulose It is anticipated that a combination of these methods will eventually provide important data on the molecular weight and distribution of the associated polysarcharides, as well as on the nature of the associative forces

The methyl ethers of the aldopentoses and of rhamnose and fucose.

Abstract: Publisher Summary This chapter presents a set of tables of the physical characteristics of the methyl ethers of the aldopentoses and rhamnose and fucose (and their derivatives) replaces those of R. A. Laidlaw and E. G. V. Percival, Advances in Carbohydrate Chem.

The methyl ethers of D-galactose.

Abstract: Publisher Summary This chapter presents a set of tables of the physical characteristics of the methyl ethers of D-galactose and their derivatives, replaces those of D. J. Bell, Advances in Carbohydrate Chem.