Saccharide acids

The synthesis of 4 and 5 provided an opportunity to evaluate the scope of a new C-glycosidation methodology that was used for 3 (28-34). Accordingly, esterification (step A) of the glycone component, l-thio-l,2-0-isopropylidene acetal (TIA) 16 and one or the other aglycone segments, C-branched saccharide acids 14 or 15, furnishes ester 12 or 13, respectively (Scheme 1). Tebbe methylenation (step B) of the latter provides enol ethers 10 or 11. Thiol... 

Saccharide acids, formed by partial oxidation of sugars. 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

Com symps [8029-43 ] (glucose symp, starch symp) are concentrated solutions of partially hydrolyzed starch containing dextrose, maltose, and higher molecular weight saccharides. In the United States, com symps are produced from com starch by acid and enzyme processes. Other starch sources such as wheat, rice, potato, and tapioca are used elsewhere depending on avadabiHty. Symps are generally sold in the form of viscous Hquid products and vary in physical properties, eg, viscosity, humectancy, hygroscopicity, sweetness, and fermentabiHty. 

Derivatization is useful for detection of compounds such as amino acids and amines that lack easily detectable groups. For similar reasons, saccharides, as a class of compound, ehcit much interest. Two derivatization schemes have been reported using benzamide (61) and FMOC—hydrazine (62) to produce fluorescent products. 

Oligo- and higher saccharides are produced extensively by acid-and/or enzyme-catalyzed hydrolysis of starch, generally in the form of symps of mixtures (12). These products are classified by thek dextrose equivalency (DE), which is an indication of thek molecular size and is a measure of thek reducing power with the DE value of anhydrous D-glucose defined as 100. 

By far the majority of carbohydrate material in nature occurs in the form of polysaccharides. By our definition, polysaccharides include not only those substances composed only of glycosidically linked sugar residues but also molecules that contain polymeric saccharide structures linked via covalent bonds to amino acids, peptides, proteins, lipids, and other structures. 

Porphyrin-based diboronic acids as artificial receptors for saccharides 98YGK831. 

With remarkable accuracy, Democritus in the fifth century B.C. set the stage for modem chemistry. His atomic theory of matter, which he formulated without experimental verification, still stands, more or less intact, and encapsulates the profound truth that nature s stunning wealth boils down to atoms and molecules. As science uncovers the mysteries of the world around us, we stand ever more in awe of nature s ingenious molecular designs and biological systems nucleic acids, saccharides, proteins, and secondary metabolites are four classes of wondrous molecules that nature synthesizes with remarkable ease, and uses with admirable precision in the assembly and function of living systems. 

Preparation of the acetate derivative Concentrate the aqueous mixture of saccharides to approximately 0.5 ml in a 20-50 ml container. Reduce the saccharides by adding 20 mg of sodium borohydride that has been dissolved carefully into 0.5 ml of water and let the reducing mixture stand at room temperature for at least 1 hour. Destroy the excess sodium borohydride by adding acetic acid until the gas evolution stops. Evaporate the solution to dryness with clean nitrogen. Add 10 ml of methanol and evaporate the solution to dryness. Acetylate with 0.5 ml (three parts acetic anhydride and two parts pyridine) overnight. Evaporate to a syrupy residue and add 1 ml of water. Evaporate again to dryness to remove the excess acetic anhydride. Dissolve the residue in 250 /d methylene chloride. 

These results indicate that, during thermolyses of fructose-containing saccharides, di-D-fructose dianhydrides are formed readily, but subsequent isomerization is extremely slow—even in the presence of added acid. However, under these conditions, the protonating power of any acid is moot. At the high temperatures used, residual water would be driven off rapidly, unless the reaction vessel is pressurized therefore, reaction occurs in the anhydrous melt. It is presumably protonation of one of the ring oxygen atoms in the dianhydrides that constitutes the first step in isomerization, followed by scission of a C-O bond to yield one of the oxocarbenium ion intermediates postulated in Refs. 31 and 80. Such ions have also been postulated as intermediates in the isomerization of spiroketals to a more-stable product. This latter isomerization can be extremely facile 104 dilute aqueous acid,120 or non-aqueous Lewis-acid conditions121 have been used to effect such transformations. 

Finally, a huge number of different boronic and diboronic acids has been designed with the aim to use them as molecular receptors for saccharide... 

Fig. 42. A series of boronic acids 159-166 with chromophoric groups has been evaluated with respect to its capacity to selectively bind d-glucose or other saccharides...

Scheme 1. Formation of a macrocyclic complex between a diboronic acid and a saccharide...

Fig. 43. Compounds 167-171 form a series of diboronic acids for the complexation of saccharides with functional groups that permit analysis by circular dichroism measurements...

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