O-acyl cleavage

CHXOO Na + (R)-HOCH(CHj)CHjCH,. The alcohol is 2 we find O—acyl cleavage and no change in configuration of alcohol. RCOO Na forms in basic solution. 

CH,COOH + (R)-HOCH(CH,)CH,CH,. Again O—acyl cleavage occurs. 

Wells, M. A. (1971) Evidence for O-acyl cleavage during hydrolysis of 1,2 diacyl-.vw-glycero 3-phosphocholine by the phospholipase A2 of Crotalus adamantus, Bio-... 

O-acyl cleavage would lead to the formation of the following structure, not detected... 

Once structure IV is formed rapid O-acyl cleavage ensues. However, once the O-alkyl linkage is broken no more exchange is possible and ring-opening proceeds as in I. Thus, the proportion of structures like III doubles with each propagation step under the con-... 

The P-substitution stabilizes cation II and increases the proportion of the O-acyl cleavage. Lando et al.19 Z0) have found that the optical activity of poly (D- + -P-methyl-P-propiolactone) is lower than that of the monomer, indicating a simultaneous inversion (route I) and retention (II) at the P-C-4 atom. 

Hydrolysis of L-lactide gives lactic acid with the same optical purity as hydrolysis of the polymer of L-lactide. This indicates that cationic polymerization of L-lactide proceeds with retention of configuration on both C atoms, i.e. by O-acyl cleavage 21,22) ... 

Thus, the direction of the ring-opening may change by the nature of the monomer For strained 4- and 7-membered unsubstituted lactones it proceeds via O-alkyl cleavage whereas for substituted lactones O-acyl cleavage becomes important. 

Enzymatic resolution of racemates by selective A- or O-acyl cleavage (described above) requires completely acylated material. Since chemical acylation is often incomplete (even a significant excess of trifluoroacetic anhydride does not completely convert tyrosine into its... 

Rearrangement involving cleavage of the C—O bond is also observed with the phenyl isocyanate adduct (59). In place of an O-acylated nitrone its product (60) of acyl migration is isolated (67JPR(36)86). 

Fig. 1.3 The currently accepted chemical mechanism of protein splicing. 1 N-S(O) acyl shift, 2 transesterification, 3 cleavage by succinimide formation, 4 S(0)-N acyl shift.

The term acid catalysis is often taken to mean proton catalysis ( specific acid catalysis ) in contrast to general acid catalysis. In this sense, acid-catalyzed hydrolysis begins with protonation of the carbonyl O-atom, which renders the carbonyl C-atom more susceptible to nucleophilic attack. The reaction continues as depicted in Fig. 7. l.a (Pathway a) with hydration of the car-bonium ion to form a tetrahedral intermediate. This is followed by acyl cleavage (heterolytic cleavage of the acyl-0 bond). Pathway b presents an mechanism that can be observed in the presence of concentrated inorganic acids, but which appears irrelevant to hydrolysis under physiological conditions. The same is true for another mechanism of alkyl cleavage not shown in Fig. 7.Fa. All mechanisms of proton-catalyzed ester hydrolysis are reversible. 

Hydrolyses of esters of most 2° and 1° alcohols occur by cleavage of the O—acyl bond,... 

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