Carbohydrate-protecting groups

The detachment of the glycopeptide from the resin and deprotection of the amino acid side chains as well as the removal of the acid-labile carbohydrate protecting groups were simultaneously carried out using TFA/H20/thioanisole/ethanedithiol (87.5 5 5 2.5). This treatment proceeded without affecting the glycosidic bonds and furnished the target molecule 38. 

Because of the polyfunctional nature of carbohydrates, protective-group strategy plays an important role in synthetic methodology involving this class of compounds. In the present Chapter, results are described from a study of the utility of N-trimethylsilyl- and N-tert-butyldimethylsilyl-phthalimide for the selective silylation of primary hydroxyl groups in carbohydrates. Also described, is a new, facile method for cleavage of acetals and dithioacetals in carbohydrate derivatives the method involves treatment of the derivatives with a dilute solution of iodine in methanol. 

Because nuclear magnetic resonance (NMR) is particularly advantageous for carbohydrates, protecting group routes may often be shortened by the use of partial substitution reactions [4-6], followed by chromatographic separations and characterization by means of NMR. 

Stadler et al. has synthesized several sugar-grafted polysiloxanes obtained by multistep procedures, including the preparation of the protected allyl-functionalized-sugars, the hydrosilylation with a statistical poly(dimethyl-co-hydrogenomethyl)-siloxane and finally the removal of the carbohydrate protective groups. 

A number of special oxidation methods have also been applied to partially protected aldoses. The Dess-Martin periodinane, l,l,l-triacetoxy-l,l-dihydro-l,2-benziodoxol-3(l//)-one [31], is a mild and efficient oxidant compatible with carbohydrate protecting groups [25]. However, it is also quite expensive and should only be used if the other procedures fail. The hydrogen transfer reactions catalyzed by 5% of RhH(PPh3)4 can also be applied to partially protected aldoses [8]. 

H. Yu, D. L. Williams, and H. A. Ensley, 4-Acetoxy-2,2-dimethylbutanoate A useful carbohydrate protecting group for the selective formation of fi-( 1 3)-D-glucans, Tetrahedron Lett., 46 (2005)... 

S. Bhattacharyya, B. G. Magnusson, U. Wellmar, and U. J. Nilsson, The p-methoxybenzyl ether as an in situ -removable carbohydrate-protecting group a simple one-pot synthesis of the globotetraose tetrasaccharide, J. Chem. Soc. Perkin Trans. 1, 8 (2001) 886-890. 

As fluorous Cbz-type hnkers are known to be partially deprotected in acidic medium, a base-labile amine-protecting group (19, Scheme 8.4) was developed as an orthogonal alternative. The peptide products were purified by both fluorous HPLC and FSPE [41]. The deprotection of the fluorous tag was carried out using 2% aqueous ammonia, a reagent that would raise concerns in the presence of common carbohydrate-protecting groups such as acetates. 

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