Deoxy Glycosides

8 Selective Glycosidation Reactions and Their Use in Medicinal Chemistry 

2-Iodo-glycosides can be a valuable alternative to the above-mentioned 2-bromo derivatives. Easily prepared via addition reactions to glycals of NIS or I(coIl)2C104 and alcohols [30,157], these donors were successfully used in the synthesis of aureolic acid oligosaccharides [155,156,158]. 

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Scheme 5.56 Routes to 2-amino-2-deoxy-glycosides from glycals.

A reaction which is analogous to the orthoester synthesis but which utilises glycosyl oxazolines affords means of synthesising, 2-trans-2 amino-2-deoxy-glycoside derivatives. Treatment of the gluco compomd (17) with phenol in the presence of toluene- -sulphonic acid thus gave the glycoside (18), and it was also utilised in a nucleoside synthesis 48). 

Nonstereoselective reductive samariations on 2-deoxy glycosides, though of limited synthetic value, are nevertheless of mechanistic interest. However, this type of process does have utility in the preparation of C(2)-oxygenated or C (2)-aminated C-glycosides which is described in Sect. 2.2.3. 

In recent studies, acceptable yields of (3-configurated 2-deoxy glycosides by application of the NIS reaction to uronic ester glycals like 38 have been reported [19]. By NMR studies the equilibrium conformation of the glycal 38 is shown to be shifted towards the inverted half-chair or half-boat conformation [5H4(D)]. 

Deoxy-glycosides have been prepared on solid support by employing a sulfonate-based linker that can be cleaved by nucleophilic attack.59... 

Nicolaou KC, Mitchell HJ, Flyaktakidou KC, Suzuki H, Rodriguez RM, 1,2-Seleno migrations in carbohydrate chemistry Solution and solid-phase synthesis of 2-deoxy glycosides, orthoesters, and allyl orthoesters, Angew. Chem. Int. Ed., 39 1089-1093, 2000. 

Scheme 33. Br as the stereodirecting group in the preparation of 2-deoxy- -glycosides...

Scheme 34. Routes to 2-deoxy- -glycosides from glycals...

Although not all of the listed promoters have been applied to the synthesis of 2-deoxy glycosides it is reasonable to assume that they can also be used for this purpose... 

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