N^αacyl‐aminoacid amides as O‐acylating reagents of serine

Intramolecular reaction of specific substrate as a step in α‐chymotrypsin catalyzed hydrolysis

“…The spectrophotometric pattern of the enzymatic reaction, the absence of tile hydrolysis product of the substrate (FA-Try) at the time corresponding to the maximum absorbance as well as analogous phenomena reported to occur with FA-Tyr-O-Me [12] and FA-Tyr-OEt [11] lead to the conclusion that the formation of the oxazolinone occurs between the Michaelis complex and the acylenzyme. This is in agreement with the rapid reaction of oxazolinone with t~-chymotrypsin to form the acylenzyme [13,14] while no formation of oxazolinone has been observed during the deacylation of acylenzyme [15]. In other words the oxazolinone can be proposed as a highly reactive intermediate in the acylation step of a-chymotrypsin by Na-acylated amino acid derivatives at acidic pH.…”

“…Oxazolinones (III) can also be obtained from _Na-acylated amino acid amides (I) through an intramolecular nucleophilic displacement catalyzed by an anhydrous acid solvent [16] In this case the electrophilicity of the ultimate carbonyl carbon is enhanced by the solvent protonation. It is noteworthy that in anhydrous acidic medium an A macyl amino acid amide (I) easily reacts with serine through the oxazolinone (III) intermediate [8] to yield an Na-acyl amino acyl-O-serine (V) which can be considered as a chemical equivalent of the acylenzyme:…”

“…By this procedure only the oxazolinone derivatives give a positive test: for the ester derivatives longer incubation with NH2OH at higher temperature is necessary. In a parallel experiment the residue was allowed to react with serine in anhydrous TFA 10 min at room temperature, as previously described [8], as an additional test for the presence of the oxazolinone derivative. The reaction product was chromatographied on Whatman no.…”