Publisher Summary This chapter provides an overview of the 13 Carbon-nuclear magnetic resonance ( 13 C-NMR) spectroscopy of monosaccharides. The 13 C-NMR spectroscopy has become increasingly important as a tool for the characterization and structural elucidation of sugars and their derivatives. Although 13 C-NMR is closely related to 1 H-NMR spectroscopy, especially when both types of spectra are recorded with Fourier-transform instruments, the two techniques are sufficiently different to be valuable complements to each other. In many cases, in particular when dealing with complex molecules such as polysaccharides, the amount of information obtainable from 1 H-NMR spectra is limited as compared to that revealed by 13 C- NMR spectra. This chapter provides an almost complete collection of 13 C- NMR chemical shifts of monosaccharides, their methyl glycosides, and acetates, along with the examples of shift data for as many different types of monosaccharide derivative as possible. It also provides details on sampling techniques and assignment techniques, and discusses the identity of monosaccharides, their structure determination, and conformational analysis .

Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Monosaccharides

Glycoproteins, glycolipids, and glycophospholipids (glycoconjugates) are components of membranes. The oligosaccharide residue is responsible for intercellular recognition and interaction; it acts as a receptor for proteins, hormones, and viruses and governs immune reactions. These significant activities have stimulated interest in oligosaccharides and glycoconjugates. With their help it should be possible to clarify the molecular basis of these phenomena and to derive new principles of physiological activity. Major advances in the synthesis of oligosaccharides have been made by the use of the Koenigs-Knorr method, in which glycosyl halides in the presence of heavy-metal salts are employed to transfer the glycosyl group to nucleophiles. The disadvantages of this procedure have led to an intensive search for new methods. Such methods will be discussed in this article. Emphasis is placed on glycoside and saccharide formation by 1-O-alkylation, on the trichloroacetimidate method, and on activation through the formation of glycosylsulfonium salts and glycosyl fluorides.

New Methods for the Synthesis of Glycosides and Oligosaccharides—Are There Alternatives to the Koenigs‐Knorr Method? [New Synthetic Methods (56)]

Xanthan gum: production, recovery, and properties.

Of late, the most bountiful natural biopolymer chitin and chitosan have become cynosure of all party because of an unusual combination of biological activities plus mechanical and physical properties. However applications of chitin are limited due to its inherent insoluble and intractable nature. Chitosan, alkaline hydrolytic derivative of chitin has better solubility profile, less crystallinity and is amenable to chemical modifications due to presence of functional groups as hydroxyl, acetamido, and amine. The chemical modification of chitosan is of interest because the modification would not change the fundamental skeleton of chitosan, would keep the original physicochemical and biochemical properties and finally would bring new or improved properties. In view of rapidly growing interest in chitosan its chemical aspects and chemical modification studies is reviewed. The several chemical modifications such as oligomerization, alkylation, acylation, quternization, hydroxyalkylation, carboxyalkylation, thiolation, sulfation, phosphorylation, enzymatic modifications and graft copolymerization along with many assorted modifications have been carried out. The chemical modification affords a wide range of derivatives with modified properties for specific end use applications in diversified areas mainly of pharmaceutical, biomedical and biotechnological fields. Assorted modifications including chitosan hybrids with sugars, cyclodextrin, dendrimers, and crown ethers have also emerged as interesting multifunctional macromolecules. The versatility in possible modifications and applications of chitosan derivatives presents a great challenge to scientific community and to industry. The successful acceptance of this challenge will change the role of chitosan from being a molecule in waiting to a lead player.

Chitosan-modifications and applications: Opportunities galore

In the reactions used to break heparin down to mono- and oligosaccharides, androsugars are formed at two stages. The first of these is the well-known cleavage of heparin with nitrous acid to convert the N-sulfated D-glucosamines to anhydro-D-mannose residues; this reaction has been studied in detail. It is demonstrated here that only low pH (less than 2.5) reaction conditions favor the deamination of N-sulfated D-glucosamine residues; the reaction proceeds very slowly at pH 3.5 or above. On the other hand, N-unsubstituted amino sugars are deaminated at a maximum rate at pH 4 with markedly reduced rates at pH2 or pH6. At room temperature solutions of nitrous acid lose one-fourth to one-third of their capacity to deaminate amino sugars in 1 h at all pHs. A low pH nitrous acid reagent which will convert heparin quantitatively to its deamination products in 10 min at room temperature is described, and a comparison of the effectiveness of this reagent with other commonly used nitrous acid reagents is presented. It is also shown that conditions used for acid hydrolysis of heparin convert approximately one-fourth of the L-iduronosyluronic acid 2-sulfate residues to a 2,5-anhydrouronic acid. This product is an artifact of the reaction conditions, and its formation represents one of several pathways followed in the acid-catalyzed cleavage of the glycosidic bond of the sulfated L-idosyluronic acid residues.

Formation of anhydrosugars in the chemical depolymerization of heparin.

A preparative synthesis of 3-amino-2,3,6-trideoxy-L-lyxo-hexose (daunosamine) hydrochloride from D-mannose.

Large-scale preparation of D-allose: observations on the stereoselectivity of the reduction of 1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranos-3-ulose hydrate

The nitrous acid deamination of glycosides and acetates of 2-amino-2-deoxy-D-glucose

This article surveys methods for the enzymatic conversion of starch, involving hydrolases and nonhydrolyzing enzymes, as well as the role of microorganisms producing such enzymes. The sources of the most common enzymes are listed. These starch conversions are also presented in relation to their applications in the food, pharmaceutical, pulp, textile, and other branches of industry. Some sections are devoted to the fermentation of starch to ethanol and other products, and to the production of cyclodextrins, along with the properties of these products. Light is also shed on the enzymes involved in the digestion of starch in human and animal organisms. Enzymatic processes acting on starch are useful in structural studies of the substrates and in understanding the characteristics of digesting enzymes. One section presents the application of enzymes to these problems. The information that is included covers the period from the early 19th century up to 2009.

Derek Horton

Papers

A preparative synthesis of 3-amino-2,3,6-trideoxy-L-lyxo-hexose (daunosamine) hydrochloride from D-mannose.

Large-scale preparation of D-allose: observations on the stereoselectivity of the reduction of 1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranos-3-ulose hydrate

The nitrous acid deamination of glycosides and acetates of 2-amino-2-deoxy-D-glucose

Enzymatic conversions of starch.

1,2:3,4-di-O-isopropylidene-α-D-galacto-hexodialdo-1,5-pyranose and its 6-aldehydrol