De-O-acylation

Hollingsworth, R.I., Lill-Elghanian, D.A. Isolation and characterization of the unusual lipopolysaccharide component, 2-amino-2-deoxy-2-JV-(27-hydroxyoctacosanoyl)-3-0-(3-hydroxy-tetradecanoyl)-gluco-hexuronic acid, and its de-O-acylation product from the free lipid A of Rhizobium trifolii ANU843. J Biol Chem 264 (1989) 14039-14042. 

Less surprising is de-O-acylation in the presence of lipases. This can also be selective in polyacylated derivatives,... 

In the methanolysis procedure, as used for the standard quantitative monosaccharide GLC analysis of glycoconjugates [240,241], 1 M methanolic HCl (24 h, 85 C) is applied. However, under these conditions released sialic acids are completely de-Af,0-acylated, which makes this approach unsuitable for the characterization of different types of sialic acid. It is, however, a reliable approach for the determination of the total amount of a mixture of (0-acetylated) A-acylneuraminic acids. When using a milder methanolysis procedure (0.05 M methanolic HCl, 1 h, 80 C) the de-iV-acylation but not the de-O-acylation is strongly reduced [242]. 

Free as well as glycosidically bound sialic acid give rise to highly characteristic H NMR parameters. The H NMR spectra are generally recorded in D2O, and because of the pH dependency of the proton chemical shifts, the spectral data are standardized at pD 6-7. The choice of the pH is also of importance in view of the earlier discussed de-O-acylation, 0-acyl migration, and autohydrolysis. 

To prepare the a anomer (60) of the aminonucleoside [ namely, 9-(3-amino-3-deoxy-)8-D-ribofuranosyl)-iV , lV -dimethyladenine], 9-(3-ac-etamido-3-deoxy-a-D-arabinofuranosyl) -JV , iV -dimethyl-2- (methylthio) -adenine (59) was prepared by condensation of the titanium chloride complex of 3-acetamido-l-0-acetyl-2,5-di-0-benzoyl-3-deoxy-arabinofuranose with iV ,iV -dimethyl-2-(methylthio)adenine, followed by desulfurization and de-O-acylation. The inversion of the hydroxyl group on C-2 by way of its methylsulfonyl ester then gave the desired a anomer (60) of the aminonucleoside, isolated as its vanillylidene derivative. " The A-acetyl... 

The reaction of 3,4,6-tri-0-acetyl-2-deoxy-2-phthalimido-D-glucopy-ranosyl chloride with the chloromercuri derivative of Ar ,iV -dimethyl-2-(methylthio)adenine, followed by desulfurization and de-O-acylation gave 9-(2-acetamido-2-deoxy-/3-D-glucosyl)-iV ,i -dimethyladenine (69)This... 

When 0-acylated substances are alkylated with diazoalkanes in the presence of lower alcohols, the product should not be left for long in the solution containing the excess of the reagent, since de-O-acylation may occur [56]. 

The presence of 0-acyl substituents in the C-7 to C-9 side chain of sialic acid will influence the periodate oxidation and thus the chromogen formation in the assay. The low molar extinction coefficients relative to NeuSAc (Table 1) indicate that such sialic acids are not de-O-acylated completely in the assay (Beau and Schauer 1980). The presence of 0-acetyl groups in the side chain prevents periodate oxidation (Haverkamp et al 1975) and precludes the formation of compound I (Fig. 1). This effect is complete with 0-substitution at C-7 or C-8, while C-9 substitution leads to partial blocking of oxidation. An analysis of total sialic acid... 

---