Aldose reaction with

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

From Acylated Aldoses by Reaction with a Thiol in the Presence of Lewis Acid. 181... 

A new synthetic route for functionalized polyhydroxyalkyl-pyrimidines starting from unprotected aldoses and based on montmorillonite K-10 catalysis and solvent-free microwave irradiation conditions, has been reported by Yadav et al,m Thus, reaction of D-glucose and D-xylose with semicarbazide or thiosemicarbazide (186) in the presence of montmorillonite K-10, under microwave irradiation, proceeded via domino cycloisomerization, dehydrazination, and dehydration of the intermediate semi- or thiosemicarbazones (187) to afford l,3-oxazin-2-ones or l,3-oxazine-2-thiones (188) in one single step and in yields between 79% and 85% (Scheme 34). Other mineral catalysts tested, such as silica gel and basic alumina, were far less effective for this transformation and only silica gel was active at all, giving low yields (15-28%) of compounds 188a-d. The l,3-oxazin-2-ones(thiones) thus synthesized were subsequently converted into the target pyrimidines by reaction with aromatic... 

Reducing sugars can be detected by reaction with phenylhydrazine to yield a hydrazone product, except the result of the reaction is not what one might imagine giving the structure of aldoses and ketoses. Glucose, for example, can react with phenylhydrazine to yield the anticipated... 

The reaction with ethyl acetoacetate has been extended to glycolaldehyde, and to carbohydrates other than n-glucose, by employing different experimental conditions it is probably applicable to aldoses in general. With d-fructose, yields are lower, but two molar proportions of water are liberated and a crystalline product results. This has a constitution similar to that of II but with the D-omhfno-tetrahydroxybutyl chain at the /3-position on the furan ring. The reaction has been applied successfully to other ketoses and... 

The reactivity of carbohydrates is dominated by the reactivity of the aldehyde group and the hydroxyl on its next-neighbor (/ ) carbon. As illustrated by the middle row of Fig. 2.3, the aldehyde can be isomerized to the corresponding enol or be converted into its hydrate (or hemiketal) form upon reaction with water (or with an hydroxyl-group). These two reactions are responsible for the easy cycliza-tion of sugars in five- and six-membered rings (furanose and pyranose) and their isomerization between various enantiomeric forms and between aldehyde- and ketone-type sugars (aldose and ketose). 

The reaction with aldoses and ketoses is different and the procedure may be used to distinguish between them. Free monosaccharides and glycosides do not react in an identical manner with periodic acid and this reveals information about the structure, sequence and linkage of monosaccharides or their derivatives in a polysaccharide. 

Aldoses generally undergo benzilic acid-type rearrangements to produce saccharinic acids, as well as reverse aldol (retro-aldol) reactions with j3-elimination, to afford a-dicarbonyl compounds. The products of these reactions are in considerable evidence at elevated temperatures. The conversions of ketoses and alduronic acids, however, are also of definite interest and will be emphasized as well. Furthermore, aldoses undergo anomerization and aldose-ketose isomerization (the Lobry de Bruyn-Alberda van Ekenstein transformation ) in aqueous base. However, both of these isomerizations are more appropriately studied at room temperature, and will be considered only in the context of other mechanisms. 

Transaldolase, which catalyzes reactions with d-erythrose 4-phosphate and D-fructose 6-phosphate as substrates. As in the case of fructose-1,6-bisphosphate aldolase, this enzyme uses a e-amino side-chain to form a Schiff base intermediate. In this case, however, the triose phosphate moiety is not released but is transferred to the other aldose (in this case, the aldotetrose). 

Wohl prepared the acylated nitriles of the aldonic acids by heating the aldose oximes with a mixture of sodium acetate and acetic anhydride. With careful control of the reaction, this method may be used for preparative work with fairly good results. 

A quinazolodione provides the nucleus for yet another eompound that inhibits aldose reductase. The sequence for the preparation of this agent starts with the isatoate acid (90-1) from 4-chloroantharanilic acid. Heating the compound with the substituted benzylamine (90-2) results in the formation of the ring-opened amide (90-3) with a loss of carbon dioxide. The ring is then reclosed, this time by reaction with carbonyl diimidazole, to afford the quinolodione (90-4). The anion from the reaction of this last intermediate with sodium hydride is then alkylated with ethyl bromoacetate. Saponification of the ester completes the preparation of zenarestat (90-5) [100]. 

Reaction with Fehling s (and Benedict s) reagent, aldehydes and ketones (i.e. with sugars - aldoses and ketoses) can reduce Fehling s (and Benedict s) reagents, and they themselves are oxidized. 

According to the study on Thd already mentioned above (Dizdaroglu et al. 1976), the release of Thy is connected with the formation of 2,4-dideoxypentodi-aldose [reactions (262) and (263)]. 

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