Monosaccharides, unprotected

The activation of an anomeric hydroxyl group from partially protected or unprotected monosaccharides can be achieved via 1,2-cyclic sulfite formation. A subsequent trans-ring opening with azide N3 affords one anomeric derivative exclusively 133... 

Aldonolactones are commercially available at low cost, when compared to most of the common monosaccharides. They are typically synthesized by selective anomeric oxidation of unprotected aldoses with bromine [6]. Usually the thermodynamically more stable five-membered lactone (y-lactone) predominates over the six-membered form, with the exception of o-gluconolactone, which crystallizes as the 1,5-pyranolactone (5-lactone) [7] (Scheme 1). Another method for the preparation of sugar lactones is the dehydrogenation of unprotected or partially... 

An efficient method for preparing aldono-1,4-lactones (y-aldonolactones) as the single products from oxidation of unprotected or partially protected monosaccharides was reported [9]. It consisted in treatment of the latter by catalytic amounts of [RuH2(PPh3)4], in the presence of an excess of benzalacetone (frans-4-phenylbut-3-en-2-one) as the hydrogen acceptor, in DMF. The corresponding y-lactones were... 

Abstract The telomerization of butadiene with alcohols is an elegant way to synthesize ethers with minimal environmental impact since this reaction is 100% atom efficient. Besides telomerization of butadiene with methanol and water that is industrially developed, the modification of polyols is still under development. Recently, a series of new substrates has been involved in this reaction, including diols, pure or crude glycerol, protected or unprotected monosaccharides, as well as polysaccharides. This opens up the formation of new products having specific physicochemical properties. We will describe recent advances in this field, focusing on the reaction of renewable products and more specifically on saccharides. The efficient catalytic systems as well as the optimized reaction conditions will be described and some physicochemical properties of the products will be reported. 

Examples of this reaction are found in patents [4]. It has also been used by Wagner et al. [8], Stadler et al. [29]. According to Stadler et al., with unprotected monosaccharides lactones, the reaction proceeded easily. However, when larger saccharides were used, such as an oligosaccharide terminated by an aldonolactone, the miscibility problem could not be solved. In this case, the reaction could not be... 

Although ring-chain equilibration permits the formation of many products in fully unprotected monosaccharides, the regiocontrol in the per-O-benzylation towards uniform glycoside bond formation is generally very high [379,380] (O Scheme 65). 

In this chapter, methods for oxidation, reduction, and deoxygenation of carbohydrates are presented. In most cases, the reactions have been used on aldoses and their derivatives including glycosides, uronic acids, glycals, and other unsaturated monosaccharides. A number of reactions have also been applied to aldonolactones. The methods include both chemical and enzymatic procedures and some of these can be applied for regioselective transformation of unprotected or partially protected carbohydrates. 

L-Arcanose and L-olimycose have been prepared in enantiomerically pure forms and with high stereoselectivity by Lewis-acid promoted addition of (5)-2-benzyloxypropanal to 1-tri-methylsilyl-2,3-butadiene. Depending on the nature of the Lewis acid either the syn (with TiCl4) or the anti adduct (with BF3 Et20) can be obtained. Epoxidation with lateral control by the allylic alcohol moieties and standard reactions lead to the unprotected monosaccharides [334]. Total syntheses of 2,3-dideoxy-3-C-methyl-D-maw o-heptose and of 2,3-dideoxy-2,3-di-C-methyl-D-gfycero-D-ga(acto-heptose have been realized by addition of 2-(trimethylsiloxy)furan to 2,3-0-isopropylidene-D-glyceraldehyde ((R)-37) [335]. 

For free monosaccharides, a mixture of three components was employed to obtain unprotected azides. Based on such a concept and literature data, French... 

In some cases, simple monosaccharides such as D-glucose-6-phosphate can be prepared by direct phosphorylation of the unprotected sugar. In general, however, the sugar-OH groups have to be protected while phosphorylation can be carried out at the desired position, and the protective groups afterwards removed. 

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