Carbohydrates mono- and disaccharides

Several articles within the discussed period were devoted to the synthesis of carbohydrates (mono- and disaccharides) with a fused thietane ring. Cubero et al.< 1996CAR145> synthesized a galactose thietane derivative 72 using sodium methoxide as a condensing agent (Equation 21). 

The Pd(Ph3P)4-catalyzed removal of the 0-allyl protecting group has been described for a number of systems. For example, allyl esters are efficiently cleaved to the parent acid in chemically sensitive systems such as penicillins and glycopeptides. The internucleotide phosphate linkage, protected as the allyl phos-pho(III)triester, remains intact upon deprotection under Pd(Ph3P)4 catalysis. Allyl ethers that protect the anomeric hydroxy in carbohydrates (mono- and disaccharides) are efficiently removed under Pd(Ph3P)4 catalysis in hot (80 °C) HOAc. ... 

Defaye, K. and Garcia Fernandez, J.M., Protonic and thermal activation of sucrose an the oligosaccaride composition of caramel. Carbohydrate Res., 256, Cl, 1994. Ratsimba, V. et al.. Qualitative and qnantitative evaluation of mono- and disaccharides in D-fructose, D-glucose and sucrose caramels by gas-liquid chromatography-mass spectrometry di-D-fructose dianhydrides as tracers of caramel authenticity, J. Chro-matogr. A, 844, 283, 1999. 

Carbohydrates are the most abundant, weight-wise, organic material available. Photosynthesis produces about 400 billion tons annually. The polysaccharides are generally composed of mono- and disaccharide units. 

Mukhopadhyay, B. Field, R. A., A simple one-pot method for the synthesis of partially protected mono- and disaccharide bnilding blocks nsing an orthoesterification-benzylation-orthoester rearrangement approach. Carbohydr. Res. 2003,338,2149-2152. 

Carbohydrates are diverse with respect to occurrence and size. Familiar mono and disaccharides include glucose, fructose, sucrose (table sugar), cellobiose, and mannose. Familiar polysaccharides are listed in Table 9.1 along with their source, purity, and molecular weight range. 

Even isolated mono- and disaccharides are capable of extensive hydrogen bonding, which results in extremely low vapor pressures. Attempts at vaporization of these materials results in decomposition. Volatile derivatives must be prepared and the approaches are similar to those described for amino acids. The most common derivatives are methyl or trimethylsilyl ethers and acetyl or trifluoroacetyl esters. A highly detailed review of applications of GLC to carbohydrates including over 1000 references concerning derivatization and types of columns used has been written by Dutton (69,70). 

Acetonitrile precipitation has been the subject of some papers dealing with the analysis of mono- and disaccharides in milk and dairy products, oligosaccharides in soybeans, and general methods for sugars in foods (23). Aqueous ethanol has also been frequently utilized in the extraction of lipids as undesirable components along with the carbohydrates. A further treatment with chloroform will free the hydroalcoholic extract from the lipids. 

In spite of the fact that this chromatographic technique is not generally associated with carbohydrate analysis, some applications are found in the literature where silica gel has been employed either directly or indirectly (after modification of the phase or the analytes). The use of silica gel for this purpose involves a polar eluent such as ethylformate/EtOH/H20 (6 2 1, v/v/v) and has been applied to the chromatographic separation of some mono- and disaccharides. 

Jerusalem artichokes temporarily store assimilates in several locations within the plant that are in excess to the amount needed for structural and maintenance purposes. Most of these reserves are reallocated to the tubers during bulking. While a cross section of assimilates is found in these sites, carbohydrates predominate, of which inulin is the primary storage form. In addition to mono- and disaccharides and small amounts of starch, a number of nutrients are found, many of which are phloem mobile and reallocated to the tubers during the latter part of the growing season. 

Methyl Ethers of Mono- and Disaccharides, E. L. Hirst and Elizabeth Percival, Methods Carbohydr. Chem., 2, 145 (1963). 

Interest in the rise in plasma glucose levels following consumption of different starchy foods arose because of health concerns for diabetes. Certain diabetics require a specific schedule of energy intake throughout the day. These patients require a constant supply of carbohydrate but must avoid drastic increases or fluctuations in the concentration of plasma glucose. Consequently, their nutritional treatment includes instructions to avoid rapidly absorbed sugars (mono-and disaccharides) and to consume the more slowly absorbed starches. 

Acetylation. Rapid peracetylation of carbohydrates can be effected in the presence of iodine. With more iodine and longer reaction times the selective acetolysis of primary benzyl ethers is achieved. Perbenzyl ethers of mono- and disaccharides undergo group exchange (OBn —> OAc) at the primary carbon atoms on treatment with ACjO-HOAc-ZnClj. 

With few exceptions, enzymatic processes in carbohydrates cause degradation. Enzymes are used in the form of pure or semipure preparations or together with their producers, i.e., microorganisms. Currently, semisynthetic enzymes are also in use. Alcoholic fermentation is the most common method of utilization of monosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acid fermentation is another important enzymatic process. Lactic acid bacteria metabolize mono- and disaccharides into lactic acid. This acid has a chiral center thus either D(-), L(+), or racemic products can be formed. In the human organism, only the L(+) enantiomer is metabolized, whereas the D(-) enantiomer is concentrated in blood and excreted with urine. Among lactic acid bacteria, only Streptococcus shows specificity in the formation of particular enantiomers, and only the L(+) enantiomer is produced. 

The principal nutrients of the body are of the same type as those that it uses as stores, namely, complex carbohydrates, triacylglycerol, and protein. These are hydrolyzed within the intestinal tract to produce primarily mono- and disaccharides, amino acids and small peptides, glycerol, and free fatty acids (Chapter 12). 

DIBAL (150 eq.), PhCH, 50°C, 2 h, 82% yield, perbenzylated cyclodextrin as substrate. The method is also applicable to the monodebenzylation of perbenzylated mono and disaccharides.DIBAL in combination with triiso-butylaluminum has also been used successfully to cleave benzyl groups from carbohydrates. ... 

Titanium-based catalysts, would seem particularly attractive candidates, but the pore size of e.g. TS-1, is much too small to admit even a monosaccharide. Recently a number of synthetic approaches towards mesoporous titanium containing catalysts of the MCM-41 type have appeared in the literature . In the present paper we will deseribe the use of Ti-MCM-41 materials in the oxidation of the model mono- and disaccharides methyl a-D-glucopyranoside, sucrose and a,a-trehalose, and we will discuss the effect of the zeolite synthesis on the effectiveness in these reactions. Several preparative approaches of Ti-MCM-41 have been compared in the oxidation of these model carbohydrates. 

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