Mechanism, of acylations

The mechanism of acylation with acyl halides is usually regarded as involving the acyl cation (acyl carbonium or acylium ion) ... 

FIGURE 24.12 The mechanism of acyl-CoA dehydrogenase. Removal of a proton from the u-C is followed by hydride transfer from the /3-carbon to FAD. 

Figure 1.9 The mechanism of acylation proceeds through the attack of a nucleophile, generating a tetrahedral intermediate, which then goes on to form the product.

J. Lamotte-Brasseur, G. Dive, O. Dideberg, P. Charlier, J. M. Frere, J. M. Ghuysen, Mechanism of Acyl Transfer by the Class A Serine /3-Lactamase of Streptomyces albus G , Biochem. J. 1991, 279, 213-221. 

Reactivity tests were carried out by directly feeding phenylbenzoate, in order to confirm the hypothesis formulated about the reaction network between phenol and benzoic acid. Surprisingly, phenylbenzoate yielded benzoylphenylbenzoate and phenol as the only primary products of reaction, indicating the exclusive presence of the intermolecular mechanism of acylation. Therefore, when a high concentration of phenylbenzoate is adsorbed on the catalyst, the bimolecular mechanism is quicker that the intramolecular one. 

The protonation studies are of interest in another connection. If protonation of metallocenes can be considered to be a simple form of electrophilic attack, it is possible that other types of electrophilic substitution reactions may proceed through initial coordination of the electrophile with the central metal atom (14, 93). The mechanism of acylation of metallocenes may therefore be more complex than might be expected by analogy to similar reactions of benzenoid compounds. Clearly more studies are needed along these lines, better to define specific metal effects on the properties and reactions of these remarkable compounds. 

The kinetic and structural data may be combined to give the following qualitative description of the mechanism of acylation of chymotrypsin by a good polypeptide substrate.116... 

The mechanism of acylation of lithium phenylacetylide with a Weinreb amide has been investigated (Scheme 10).71 Dimeric lithium acetylide has reacted via a mono-solvated monomer-based transition structure. The robust tetrahedral intermediate (12) forms sequentially a C(l) 2 2 mixed tetramer with the excess lithium acetylide and a 1 3 (alkoxide-rich) mixed tetramer. The stabilities of the mixed tetramers are consistent with a pronounced autoinhibition. 

Acylation of 3-amino-5-methylamino-l,2,4-thiadiazole (28) with benzoyl chloride (or arenesulfonyl chlorides) introduces one acyl group when one equivalent is employed, and three when a large excess is used to produce (29) and (30), respectively (Scheme 16). With acetic anhydride, however, acylation terminates with the formation of the 3-monoacyl derivative (65AHC(5)ll9). For the mechanism of acylation, see Scheme 3. In the case of 3,5-diarylamino-l,2,4-thiadiazoles, no triacyl derivative is obtained even when excess of acylating agent is employed. Acetyl and benzoyl chlorides give monoacyl derivatives and p-toluenesulfonyl chloride forms 3,5-di(p-toIuenesulfonyl) derivatives (65AHC(5)119). 

Section IV,FI An elimination-addition mechanism of acyl group transfer has been proposed for the decomposition of l-(JV-methylcarbamoyl)... 

H. Al-Rawi and A. Williams, Elimination-Addition Mechanisms of Acyl Group Transfer the Hydrolysis and Synthesis of Carbamates J. Am. Chem. Soc., 1977, 99, 2671. 

Tlie mechanism of acylation is very similar to that of alkylation. 

Williams, A. (1989) Goncerted mechanisms of acyl group transfer reactions. Acc. 

The mechanism of acylation may be related to that of esterification of hydroxyl groups. 

Direct electrophilic acylations of the first of these tyf>es are the most common mode of acylation (I). The mechanism of acylation, particularly of alcoholic groups, is of course essentially the same as that for esterification, so for further consideration the relevant section of Chapter... 

Lipoic acid presumably functions only when acyl generation and transfer occur and not in decarboxylation or aceton formation. The mechanism of acyl generation suggested in reaction 2, Fig. 4, is the carbanion cleavage of the disulfide bond to form the free thioester wuth CoA and the free sulfhydryl of lipoic acid. 

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