Glucose selective esterification

Selective esterification of 2-acetamido-2-deoxy-D-glucose in pyridine and of benzyl 2-acetamido-/i,6-0-benzylidene-2-deoxy-oC-D-glucopyranoside with long-chain fatty acid chlorides gave the 6-0-acyl and 3-0-acyl derivatives respectively. The products were used as surfactants (after removal of the benzylidene acetal from the... 

Selective esterification of a given HO-group is also possible. For example, glucose can be selectively acetylated in position 3 by reacting 1,2,5,6-di-O-isopropylidene-a-D-glucofuranose with acetic acid anhydride, followed by hydrolysis of the diketal ... 

Use of acetyl chloride in dichloromethane in the presence of 2,4,6-collidine or some other bulky base allowed selective esterification at primary sites the 5-(9-acetate 11, for example, was obtained in 91% yield from the 3,5-diol 10. Bis(2-oxo-oxazolidin-3-yl)phosphinic chloride (BOP-Cl), a new reagent for condensing alcohols and acids, has been employed in the preparation of primary esters 12. Treatment of unprotected methyl a-D-glucopyranoside, 2-acetamido-2-deoxy-D-glucose, and maltose with triphenylphosphine, DEAD, and an equimolar amount of a carboxylic acid (e.g.benzoic, methacrylic or adamantoic acid) allowed regioselective 6-0-esterifrcation (0-6 for... 

Sorbitol. Sorbitol is the sugar alcohol obtained by reduction of glucose and it can be dehydrated to either isosorbide or to 1,4- and 2,5-sorbitan in acid or base catalyzed processes, respectively. Using sulfonic acid functionalized MCM-41 type materials lauric acid esters of isosorbide can be achieved quite selectively starting from sorbitol (>95% selectivity towards isosorbide dilaurate at 33% lauric acid conversion) in a dehydration-esterification... 

Fatty acids of sugars are potentially useful and fully green nonionic surfactants, but the lipase-mediated esterification of carbohydrates is hampered by the low solubility of carbohydrates in reaction media that support lipase catalysis in general. Because the monoacylated product (Figure 10.8) is more soluble in traditional solvents than is the starting compound, the former tends to undergo further acylation into a diester. In contrast, the CaLB-catalyzed esterification of glucose with vinyl acetate in the ionic liquid [EMIm][BF4] was completely selective. The reaction became much faster and somewhat less selective when conducted in... 

The synthesis of long-chain fatty acid esters of carbohydrates is inherently more demanding. It was found that glucose did not react with vinyl laurate in a pure ionic liquid medium, but in biphasic tert-butyl alcohol/[BMIm][PF6], glucose could be acylated by the vinyl esters of O, 2-Cu, fatty acids. The best results were obtained with CaLB, which was twice as active as TIL, and the selectivity for acylation at C-6 was high [114]. The esterification of glucose with palmitic acid, which is, in an industrial context, to be preferred over transesterification, has recently been demonstrated in tert-butyl alcohol/[BMIm][PF6] medium [115]. 

The incorporation of cyclic carbohydrates into Gemini surfactants was developed by Castro et al. (Rg. 7.27) [56]. These sugar geminis have been synthesized from AGs which can be easily prepared via a Rsher-type glycosylation reaction of free glucose by w-butanol. Convenient protection of the sugar moiety, followed by selective deprotection of the primary alcohol, permits the formation of gemini 12 by a double esterification with propanedicarboxylic acid. 

Further examples of selective acylations and deacylations by means of enzymes, especially lipases, have been reported. Acetylation at the primary centre of H acetylneuraminic acid was performed by acyl transfer from 2,2,2-trichloroethyl acetate under catalysis porcine pancreatic lipase in pyridine, and use of an immobilised microbial lipase in a solvent-free process allowed selective 6-0-esterification of ethyl a-D-glucopyranoside with long-chain fatty adds. Under the same conditions methyl a-D-glucopyranoside and D-glucose reacted similarly but at much slower rates. ... 

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