Hydroxyl groups in sugars

Protection, for diequatorial vicinal diols, 77, 218 of trans-hydroxyl groups in sugars, 75, 173 table, 75, 174... 

Fig. 20.1. Chemical structure of RNA with sequence. .. pApOpUpCp... or, in short, AOUC. All hydrogen atoms are drawn in adenosine, and only functional hydrogen atoms are given in the other nucleotide units. In DNA, hydroxyl groups in sugar 2 -position are replaced by hydrogen atoms, and uridine is methylated in 5-position and called thymidine [522]...

EDC is also used to couple cattle serum albumin with a synthetic glycopeptide. DCC is used to activate hydroxyl groups in sugars. The coupling of nitroxide spin labeled species to monosaccharides is also accomplished using DCC. ... 

Benzyl ethers are commonly used to protect hydroxyl groups in sugars. Benzyl halides are easily introduced because they are highly reactive in ivi2 reactions. Sodium or potassium hydride is typically used as the base in an aptotic solvent such as DMF or DMSO. The benzyl groups can later be easily removed by hydrogenolysis using a palladium catalyst. 

Silyl ethers, including tert-butyldimethylsilyl (TBS) ethers (Section 11.HE) and phenyl-substituted ethers, are also used as protecting groups in carbohydrate synthesis. tert-Butyldiphenylsilyl (TBDPS) ethers show excellent regioselectivity for primary hydroxyl groups in sugars, such as at C6 in a hexopyranose. 

Since an acetal is produced by the reaction of a carbonyl with a diol, an acetal can serve as a protective group for either functional group. Deprotection is accomplished as usual by treatment with acid and water hydrolysis of the acetal regenerates both the carbonyl and the diol. Both 1,2- and 1,3-Diols can be protected by reaction with acetone and acid. The resulting cyclic acetal (called an acetonide) is widely used in carbohydrate chemistry to selectively mask pairs of hydroxyl groups in sugars. 

The close correspondence of many of the hydroxyl groups in sugars with oxygen positions in the ice lattice probably correlates best with water at certain temperatures (that is, an ice lattice with slightly expanded dimensions to fit water oxygen distances at biological temperatures). 

Various new partial and regioselective acylations and deacylations by chemical or by enzymic means have been reported. Selective formylation of primary hydroxyl groups in sugars has been achieved by use of 99% formic acid at ambient temperature. The 6-0-formyl products, e.g., 6-0-formyl-D-glucopyranose, 6-0-formyl-D-fructofuranose, and 1,6-di-... 

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