Carbohydrates hydroxyl groups

Acequinocyl, 14 349 Acesulfame-K, 12 41-42 24 233-234 Acesulfame-K-aspartame blends, 24 233 Acetalation, carbohydrate hydroxyl groups, 4 712... 

Isomerization, 12.T63, 404 of n-butane, 13 697 butylenes, 4 409-410, 410t carbohydrate hydroxyl groups, 4 712 carboxylic acids, 5 44 catalytic aerogels for, J 763t of cyclohexane, 13 706 facilitation of, 20 100 maleic, 20 99-100 maleic anhydride 492, 15 493 paraffin, 16 844... 

Besides acetyl, benzoyl, and benzyl protecting groups for the carbohydrate hydroxyl groups, silyl, isopropylidene, and p-methoxybcnzyl groups have also been employed in solid-phase glycopeptide synthesis. The synthesis of a glycopeptide... 

In the crystalline complex, solvent molecules can be bonded not only to the cation, but also to the anion and the carbohydrate. A detailed x-ray study has snown that, in sucrose NaBr 2 HjO, each Br ion has bonds to one water molecule, one Na ion, and four carbohydrate hydroxyl groups.00 The ability of a complex to possess solvent of crystallization, even when the free individual components themselves are incapable of doing so under the same conditions of temperature, is exemplified by the formation of sucrose Nad 2 H2O at room temperature. Sucrose and sodium chloride crystallize from their aqueous solutions in the nonhydrated form. 

Configurational relationships and neighboring-group effects are undoubtedly of primary importance in modifying the behavior of carbohydrates. In this connection certain types of reactions, which are reasonably well established, are described in this section because they are of importance for the explanation of the selective reactions of carbohydrate hydroxyl groups. 

Methods now available for the partial protection of carbohydrate hydroxyl groups by alkylation are critically evaluated. Of the numerous alkyl protecting groups known, only those widely used in synthetic chemistry of saccharides are discussed. Benzyl, allyl, triphenylmethyl and other arylalkyl ethers, trimethylsilyl, rer/-butyidimethylsilyi, and rm-butyldiphenylsilyl ethers are the main topics of the article. 

OH — X. Pi. carbohydrate hydroxyl group can be replaced by halogen (bromine, chlorine, iodine) by treatment in DMF with 2 eq. each of triphenylphosphine and an N-halosuccinimidc. The by-products are succinimide and triphenylphosphine oxide. Yields are generally high. Primary hydroxyl groups can be selectively replaced in the presence of secondary hydroxyl groups. 

P.D.J. Grootenhuis and C.A.G. Haasnoot, A charmm based force-field for carbohydrates using the cheat approach -carbohydrate hydroxyl-groups represented by extended atoms Mol. Simul., 10 (1993)75. 

Carbohydrate hydroxyl groups are alkylated in three contexts analysis of polysaccharide sequences, dealt with in Section 4.2.1 protection of OH groups during synthetic transformations, which requires the alkyl residues to be removable and the modification of cheap polysaccharides, such as starch and cellulose, for more desirable properties. 

P. D. J. Grootenhuis and C. A. G. Haasnoot, Mol. Simulation, 10, 75 (1993). A CHARMm Based Force Field for Carbohydrates Using the CHEAT Approach Carbohydrates Hydroxyl Groups Represented by Extended Atoms. 

Other reactions of carbohydrates include those of alcohols, carboxylic acids, and their derivatives. Alkylation of carbohydrate hydroxyl groups leads to ethers. Acylation of their hydroxyl groups produces esters. Alkylation and acylation reactions are sometimes used to protect carbohydrate hydroxyl groups from reaction while a transformation occurs elsewhere. Hydrolysis reactions are involved in converting ester and lactone derivatives of carbohydrates back to their polyhydroxy form. Enolization of aldehydes and ketones leads to epimerization and interconversion of aldoses and ketoses. Addition reactions of aldehydes and ketones are useful, too, such as the addition of ammonia derivatives in osazone formation, and of cyanide in the Kiliani-Fischer synthesis. Hydrolysis of nitriles from the Kiliani-Fischer synthesis leads to carboxylic acids. 

Alkylation Carbohydrate hydroxyl groups react with alkyl halides, especially methyl and benzyl halides, to give ethers. 

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