Sugars hydroxyl group

The chemical transformations of dialkyl dithioacetals have been reviewed in detail [47] and offer routes to a variety of useful carbohydrate derivatives. Dialkyl dithioacetal derivatives of sugars continue to play an important role in modem synthetic carbohydrate chemistry through reactions of die dithioacetal function and manipulation of the sugar hydroxyl groups. Dithioacetals also provide a convenient method for temporary protection of sugar carbonyl groups in the synthesis of noncarbohydrate natural products. 

Finally, the sugar hydroxyl groups of nucleosides are weakly acidic only, with pATa values usually >15 (20). An exception is the ribose with its 2, 3 -diol groups, which undergoes deprotonation with p> 12.5 due to a favorable stabilization of the deprotonated group via hydrogen-bond formation. 

Chemical synthesis, limited by complex synthetic approaches using protection of the sugar hydroxyl groups in order to achieve regioselectivity, and more so stereoselective reactions... 

Different authors tried to perform directly the hydrosilylation of unprotected sugars. It would avoid time-consuming protection-deprotection steps. It would avoid also the risk of equilibration of the silicone backbone occuring under the acid or basic deprotection conditions. Usually the sugar hydroxyl groups react with hydrosilanes to form silylethers, namely Si-O-C bonds in the presence of a hydrosilylation catalyst. This dehydrocondensation side reaction has to be controlled in order to avoid cross-linking, by using selected solvents and catalysts. 

DCC is also used in nucleotide chemistry to esterify a sugar hydroxyl group with a phosphate group in another nucleotide or oligonucleotide unit. Also p-styrene based polymers with a pyridyl-2-ethanol end group are reacted in pyridine with 3 -0-acetyl-desoxythimidine-5 -phosphate in the presence of DCC." The reaction of mono esters of phosphoric acid with alcohols or phenols, in the presence of DCC, affords phosphoric acid diesters in high yield." This reaction is widely used in nucleic acid chemistry. 

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