Carbohydrates aldehydes

A reaction of practical importance is the oxidation of a carbohydrate aldehyde group to a carboxyl group. This is the basis for a process converting glucose to calcium gluconate, a substance of pharmaceutical interest. The oxidation reaction occurs at graphite electrodes in the presence of the Brj/Br" redox system. Calcium salt is added to the solution to prevent further oxidation of free gluconic acid. 

With these results in hand, examination of the generality of the method as well as its application to the condensation of unstabilized carbohydrate ylides with carbohydrate aldehydes was undertaken. At... 

Condensation of the ylide derived from X with carbohydrate aldehyde X proceeded smoothly to afford only the Z-isomer XIII. Proof of the olefinic configuration was garnered by photochemical isomeri-... 

Aldehyde Amine carbohydrates Aldehyde-amine Schiff base or glycosylamine... 

In the case of a carbohydrate-aldehyde source, an isomeric mixture of products is to be expected, consisting mainly of the F-isomcr and some of the Z-form of the open-form sugar alkoxime and only minor amounts of the two anomeric pyranosyl oximes (Fig. 26) [179],... 

Fig. 26 An isomeric mixture is expected when preparing sugar alkoximes from a carbohydrate-aldehyde source...

Reduction of a-oxy carbonyl compounds. The reductive cleavage of the C-0 bond may lead to more extensive structural changes, such as those that occur in the case of a carbohydrate aldehyde. The dialdehyde is labile, forming a cyclopentane derivative as a ring-contraction product. 

On the biodegradable material, in the case of the carbohydrates aldehyde or hydroxyl groups in the case of proteins and urea amine groups, and... 

In addition to sugars and their degradation products and the degradation products of amino acids (amines, ammonia and aldehydes), these reactions also include carbonyl compounds already present in foods as primary substances (e.g. aldehydes and ketones occurring in essential oils), ascorbic acid and carbonyl compounds formed in foods from precursors other than carbohydrates (aldehydes resulting from fat oxidation), thereby the reactions become even more complex. 

X = SnMe3 (19) X = SnMe2l reaction with a carbohydrate aldehyde. ... 

Another reductive coupling technique has been applied to unsaturated carbohydrate aldehydes, giving cyclopentanes with high stereoselectivity following samarium diiodide reduction, as exemplified in Scheme 12. ... 

Treatment of hexopyranosid-2-ulose derivatives with DAST pioduced the gem-difluorides only if both neighbouring groups were either axial or equatorial. The stereoselective aldol coupling of 2-deoxy-hexopyranosid-3-uloses with various carbohydrate aldehydes is covered in Chapter 14. The chemoselective reduction of enones in the presence of allyl ethers by the conjugate addition of thiophenol followed by radical desulfurization with BujSnH has been achieved. ... 

Knoevenagel reactions have been carried out on 2,3 4,5-di-O-isopropylidene-aIdehydo-D-xylose with methyl acetoacetate and pentane-2,4-dione and products such as (48) have been obtained. Reactions of Wittig reagents with carbohydrate aldehydes have been used to obtain access to cyclopentanes (Chapter 18) and an isomer of Compound (47) (Chapter 24). 

Furthermore, the installation of 53w-configuration during the C—C bond formation is a consequence of a //A e-approach (/ c-side attack of acetoacetic ester to the f c-side of carbohydrate aldehyde or 5/-side attack of acetoacetic ester 19 to the 5i-side of carbohydrate aldehyde). 

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