Acylation with anhydrides

Protein functional groups able to react with anhydrides include the oc-amines at the N-terminals, the s-amine of lysine side chains, cysteine sulfhydryl groups, the phenolate ion of tyrosine residues, and the imidazolyl ring of histidines. However, acylation of cysteine, tyrosine, and histidine side chains forms unstable complexes that are easily reversible to regenerate the original group. Only amine functionalities of proteins are stable to acylation with anhydride reagents (Fraenkel-Conrat, 1959 Smyth, 1967). 

PEG contains no carboxylate groups in its native state, but can be modified to possess them by reaction with anhydride compounds. Either PEG or mPEG may be acylated with anhydrides... 

A similar approach uses the potassium enolate and achieves acylation with anhydrides or acylimidazoles in addition to acid chlorides (80TL2773). 

These derivatives for the analysis of amino acids have been widely investigated and various combinations of acyl and alkyl groups have been tested in order to find the properties most suitable from the viewpoint of chromatography, the reaction yields and the reaction time for the whole group of amino acids. Their preparation is based on the first, i.e., esterification step, when common esterification reactions are applied with minor modifications, and the second step, when amino and other functional groups are acylated with anhydrides, chlorides or other acylating agents. 

The more reactive aromatic ethers are acylated with anhydrides over clayzic or clayfen. 2-MN selectively gives 1-acetyl derivative 28 in 71% yield at 80°C in nitrobenzene, whereas at 140°C the yield increases until 82% but a drop in selectivity is observed, small amounts of thermodynamically favored 6-acylated product 29 ( 7%) accompanied by the 8-acylated product 30 ( 2%) being obtained via protiodeacylation (Scheme 4.20). 

Table 4.19 Anisole acylation with anhydrides in the presence of SZ...

It is now evident that acylation with anhydrides (such as acetic and succinic anhydrides) and with lactones (such as -propiolactone) is being proposed (< ) for improving the solubility of soy protein isolates at acidic pH, particularly for the preparation of coffee whiteners. Moreover, this chemical modification has been evaluated for altering the food-use properties of several milk proteins (40), egg protein (41), wheat protein (42), fish protein (43), and single-cell protein (44). 

Friedel-Crafts acylation. The catalyst combined with TfOH in MeCN is an effective promoter of arene acylation with anhydrides at room temperature (14 examples, 61-98%). 

Acylation with anhydrides, catalysed by phosphoric acid, is an efficient method reaction with acetyl p-toluenesulfonate, in the absence of any catalyst, produces 2-acetylthiophene in high yield. " Vilsmeier formylation leads efficiently to 2-formylthiophene. ... 

Another important derivatization method of hydroxy compounds is their acylation with anhydrides of acetic, trifluoroacetic, heptafluorobutyric, etc. The latter enable very sensitive quantification to be performed using the electron-capture detector. 

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