Carbohydrates protection

TIPDSCI2, DMF, imidazole. This reagent is primarily used in carbohydrate protection, but occasionally it proves valuable in other circumstance s." ... 

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. 

Sola-Penna, M., A. Ferreira-Pereira, A.P. Lemos, and J.R. Meyer-Femandes. 1997. Carbohydrate protection of enzyme structure and function against guanidinium chloride treatment depends on the nature of carbohydrate and enzyme. Eur J Biochem 248 24—29. 

Keywords Carbohydrate Chemistry, Carbohydrate Protection, Epimerization, Inversion, Dynamic, Regioselective Control, Neighboring Group Participation... 

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. 

C.-C. Huang, C.-T. Chen, Y.-C. Shiang, Z.-H. Lin, and H.-T. Chang, Synthesis of fluorescent carbohydrate-protected An nanodots for detection of concanavalin A and Escherichia coli, Anal. Chem., 81 (2009) 875-882. 

To overcome these problems, 1,1,2,2-tetramethoxycyclohexane (TMC) 2 was developed as an alternative to bis-DHP for carbohydrate protection (Scheme 2) [28]. Initially, TMC 2 was easily prepared from inexpensive cyclohexane-1,2-dione although it is currently commercially available. TMC 2 allows the use of more polar solvents, such as methanol, and cyclohexane-1,2-diacetals (CDA) are obtained in higher yields than the corresponding dispiroketals. 

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. 

Protection of Carbohydrates. Protected carbohydrates (4 and 5), having one free hydroxyl and a phenylseleno group on the adjacent carbon, were obtained by treatment of commercially available tetra-O-acetyl- -D-ribofuranose with PhSeH/BFs Et20, followed by hydrolysis and silylation with TIPDSCI2 in pyridine (reported yields are 77-80%). As expected, the silyl chloride reacts much faster with primary than secondary alcohols, regiospecifically affording the desired protection. 

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