Carbohydrates selective protection

Some of the original work in the carbohydrate area in particular reveals extensive protection of carbonyl and hydroxyl groups. For example, a cyclic diacetonide of glucose was selectively cleaved to the monoacetonide. A summary describes the selective protection of primary and secondary hydroxyl groups in a synthesis of gentiobiose, carried out in the 1870s, as triphenylmethyl ethers. 

The selectivity here relies on the fact that the j3-benzoate is the thermodynamically more stable ester. A mixture of esters is formed upon hydrolysis of the ortho ester and is then equilibrated with DBU. Carbohydrates are selectively protected with this methodology. " ... 

As they are available from natural sources in enantiomerically pure form, carbohydrates are useful starting materials for syntheses of enantiomerically pure compounds. However, the multiple hydroxy groups require versatile methods for selective protection, reaction, and deprotection. Show how appropriate manipulation of protecting groups and/or selective reagents could be used to effect the following transformations. 

Kerekgyarto, J. Vanderven, J. G. M. Kamerhng, J. P. Liptak, A. Vliegenthart, J. F. G., Synthesis of a Selectively Protected Trisaccharide Building Block That Is Part of Xylose-Containing Carbohydrate Chains from N-Glycoproteins. Carbohydr. Res. 

The selective protection of hydroxyl groups is obviously most frequent in carbohydrate synthesis and, in fact, photosensitive protecting groups have been used to this effect in oligosaccharide synthesis, nucleotide synthesis, and saccharide modification. Here, as well as in other Sections, special attention will be devoted to 2-nitrobenzyl derivatives, whose re-... 

Cyclic acetals permit the simultaneous protection of pairs of hydroxyl groups, as such, they represent an extremely efficient protecting group. Furthermore, either 1,2 or 1,3 diols may be selectively protected rendering the use of cyclic acetals of even greater value to organic chemists in general, and to carbohydrate chemists in particular. The versatility of iodine is demonstrated in that it has been reported to be effective in both the removal and installation of cyclic acetals. 

Benzylidene and isopropylidene acetals are often used for the selective protection 1,2-cis or 1,3-cisjtrans diols of sugar derivatives. They are stable to strong basic conditions but quite fragile towards acid. Recently, dispirodiketal and cyclohexane-1,2-diacetal groups have been introduced to protect selectively 1,2-trans diols of carbohydrates. 

Amino-type groups are also present in carbohydrate molecules although the number is usually much fewer than that of the hydroxy groups. Selective protections among the amino groups are therefore less frequent. Because of their stronger nucleophilicity,... 

Thermodynamic control is important in other ways in carbohydrate chemistry, because control over ring size allows selective protection of the hydroxyl groups of sugars. Compare these two reactions. Both of them give acetals from the same starting material, mannitol. 

Based on our organocatalytic C3+C concept for the direct synthesis of carbohydrates, we envisaged the successful development of a diastereo- and enantioselective Mannich variant that paves the way to selectively protected amino sugars and their derivatives. These amino sugars are a class of carbohydrates in which one or more hydroxyl func-... 

Selective protection of primary alcohols. Selective protection of primary hydroxyl groups of carbohydrates is possible by reaction of this chlorosilane and polyvinylpyridine in CH2CI, or THF in the presence of HMPT. Amberlite A-26 in the F form is recommended for desilylation. 

As modified oligonucleotides have become a major field of investigation for chemists, methods for the suitable protection/deprotection applied to the synthesis of nucleoside monomers have become equally important. Selective protection of a multifunctional compound is a challenging problem in organic synthesis. In nucleoside chemistry, selective manipulation of the hydroxyl groups on the carbohydrate moiety over amino groups of the bases is synthetically challenging and... 

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