Acetylation of hydroxyl groups

Acetylation of hydroxyl groups and esterification of carboxyl groups have been observed ia a limited number of cases but, ia geaeral, have ao preparative advantage over chemical methods. By comparison, phosphorylation has been useful ia the preparatioa of modified purine and pyrimidine mononucleotides from their corresponding nucleosides, eg, 6-thioguanosiae [85-31-4] (51) (97). 

Another technique which has much potential in analysis, but which to date has had only limited use, is the formation of radioactive derivatives of non-radioactive compounds for quantitation by radiocounting. A radiolabeled reagent is used to form the derivative. This approach has been of use in combination with chromatography. The advantage of this technique is that it avoids problems of sample background which are often associated with spectrophotometric methods. The 14C-methylation of carboxylic acids and the 14 C-acetylation of hydroxyl groups have been studied [39,40]. These methods are quantitative and the sensitivity is dependent on the activity of the radioactive group added to the molecules. The radioactive derivatization of lipids has been reviewed [41]. 

The MMA homopolymer and the unreacted PVA are removed from the reaction product by the selective extraction method. The grafted branch PMMA is separated from the backbone by oxidative cleavage of all 1,2-glycols of PVA (about 2 mole%)29 Molar masses of the isolated graft copolymers and the separated branches are osmo-metrically determined, after acetylation of hydroxyl groups in benzene. The chemical composition of the graft copolymers is determined from the saponification value of the acetylated sample. 

In a subsequent study, the Co coordinated assembly was grafted onto a cross-linked poly(glycidoxypropylmethacrylate) (GMA)-ethylene glycol dimethacrylate (EDMA) support surface. The template and Co ions were then leached out from the matrix. This surface grafted polymer exhibited turnover, Michaelis-Menten kinetics and mechanisms such as inhibition by tosyl phenyl alanyl chloromethyl ketone and inhibition on acetylation of hydroxyl group of 2-hydroxyethylmethacry-late (HEMA), similar to native chymotrypsin. 

Bacterial resistance to chloramphenicol occurs from plasmid-mediated bacterial production of acetylase enzymes. Acetylation of hydroxyl groups prevents the drug binding to the 505 ribosomal subunit. There is less bacterial resistance to florfenicol because of the substitution of a fluorine molecule for one of the hydroxyl groups. 

Lastly, based on ab initio calculations that revealed that methyl acetate exhibits a favorable two-point interaction with CO2, Raveendran et al. suggested that acetylation of hydroxyl groups might be a possible method to solubilize hydroxylated compounds into CO2 (49). In theory, a hydrogen atom attached to the carbonyl carbon (a carbon) forms a weak yet cooperative C O hydrogen bond between the hydrogen and one of the oxygen... 

Acetylation s. 3,171 Differential acetylation of hydroxyl groups in hydroxyamino acids s. 1,183 OH -> OAc... 

Hydrolysis of hindered esters. Aranda and Fetizon observed hydrolysis of a hindered ester group accompanying deacetylation with boiling quinoline. They then found that some hindered esters are hydrolyzed when refluxed in quinoline and acetic acid. This reaction can be accompanied by acetylation of hydroxyl groups, if present. Thus methyl 18a-glycyrrhetate is converted by this procedure into the acid (43% yield), the 3 3-acetate (26% yield), and the 3a-acetate (29% yield). 

Minor changes in structure, such as methylation or acetylation of hydroxyl groups may for instance be studied in a series of alkaloids related to morphine. 

The acetylation of hydroxyl groups reduces their hydrophilicity, causes bulking of the cell wall and renders the material less susceptible to biological decay. The acetylated fibers show lower ECM, less weight loss and reduced erosion rate compared with non-acetylated fibers. 

Structure-activity studies in the rifamycin group deal with the detrimental effect of the carboxyl function,and the beneficial effect of acetylation of hydroxyl groups in the aliphatic connecting chain. 

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