Question

Propose a mechanism for stereoisomers formed when N-acetyl-L-phenylalanine is reacted with DMF, triethyl amine, L-alanine methyl ester hydrochloride and TBTU

Answer 1

In the first step triethyl amine abstracts acidic proton from N-acetyl-L-pherylalanine to form carboxylate ion which act as a nucleophile and attacks on electrophilic center of TBTU. Further kind of trans esterification gives urea as a side product and makes carboxylic acid carbonyl carbon as a good electrophilic center. Further amino group of L-alanine methyl ester attacks on the carbonyl carbon to give peptide bond formation.

In the first step triethyl amine abstracts acidic proton from N-acetyl-L-pherylalanine to form carboxylate ion which act as a nucleophile and attacks on electrophilic center of TBTU. Further kind of trans esterification gives urea as a side product and makes carboxylic acid carbonyl carbon as a good electrophilic center. Further amino group of L-alanine methyl ester attacks on the carbonyl carbon to give peptide bond formation.