Unprotected carbohydrates

TMSIH Does not react with Mino groups. Can be used to form TMS derivatives of carbohydrates in aqueous solution. Does not promote enol-ether formation with unprotected ketone groups. Most generally useful reagent, preferred for most applications. Exceptions are the formation of N-TMS derivatives and the separation of low molecular weight TMS derivatives... 

N. Jayaraman and J. F. Stoddart, Synthesis of carbohydrate-containing dendrimers. 5. Preparation of dendrimers using unprotected carbohydrates, Tetrahedron Lett., 38 (1997) 6767-6770. 

Hall, L.D., and Yalpani, M. (1980) Synthesis of luminescent probe-sugar conjugates of either protected or unprotected sugars. Carbohydr. Res. 78, C4. 

In carbohydrate chemistry, the preparation of ethers that are stable in the presence of acids, bases, and aqueous alkali is an important analytical and synthetic tool. The methods used for the etherification of hydroxyl groups51 generally employ reactions of unprotected sugars and glycosides with methyl, allyl, benzyl, triphenylmethyl, and alkylsilyl halides in the presence of a variety of aqueous and nonaqueous bases. 

Synthesis of a Polymer Possessing Unprotected Carbohydrate Residues... 

Irradiation of unprotected carbohydrates was the subject of greatest photochemical interest to the early carbohydrate photochemists.1 The investigations of these early workers were concerned primarily with the effect of reaction conditions upon the photochemical process, rather than with the identity of the reaction products. Between 1960 and 1969, a comprehensive series of papers was published on the photochemical reactions of D-glucose and D-glucitol.95-99 These studies contributed greatly to understanding of the photochemistry of unprotected carbohydrates, as not only was the result of variation in the reaction conditions studied but also the structures of the products were determined. 

Compounds 100 and 101, unprotected carbohydrates containing a phosphate group, exhibit in photochemical reactivity a marked similarity to other unprotected, carbohydrate systems188-191 (see Scheme... 

By treating Nafion (NR-50), a perfluorinated acidic ion exchanger based on sulfonic acid groups, with scandium(III) chloride hexahydrate Kobayashi et al. generated a solid scandium-derived catalyst (29) (Nafion-Sc) that proved to be effective in al-lylation reactions of carbonyl compounds with tetraallyltin (Scheme 4.15). Since the catalyst is stable in both organic solvents and water, even unprotected carbohydrates could be transformed directly in aqueous solvents. The resulting homo-allylic alcohols were separated by simple filtration [97]. 

Table 3 Reaction conditions and results for the condensation of unprotected carbohydrates with...

Acetals of o-GlcpNAc 28a (Z=NHAc) [99] and o-Glcp 28b [55] were prepared by condensation of the appropriate aldehyde or aldehyde dimethyl acetal with the unprotected carbohydrate. An improvement of the classical methods of acetalation (microwave irradiation of montmorillonite) made it possible to synthesize various 5,6-0- -alkylacetals of L-galactono-1,4-lactone [100]. 

Asymmetric C-C bond formation is the most important and most challenging problem in synthetic organic chemistry. In Nature, such reactions are facilitated by lyases, which catalyze the addition of carbonucleophiles to C=0 double bonds in a manner that is classified mechanistically as an aldol addition [1]. Most enzymes that have been investigated lately for synthetic applications include aldolases from carbohydrate, amino acid, or sialic acid metabolism [1, 2]. Because enzymes are active on unprotected substrates under very mild conditions and with high chemo-, regio-, and stereoselectivity, aldolases and related enzymes hold particularly high potential for the synthesis of polyfunctionalized products that are otherwise difficult to prepare and to handle by conventional chemical methods. 

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