Abstract
The reactions of N-succinimidyl benzoates (1) with various amino acids (2) to give the corresponding N- (arylcarbonyl) amino acids (3) were studied kinetically at 25°C and pH=pKa. The formation of (3) was competitive with the decomposition of (1) in aqueous solution; i.e., the rate may be expressed as V= (k1, d+k2 [2]) [1], where k1, d is the first order rate constant for the N-arylcarbonylation of (2) by (1).
The second order rate constant, k2, at pH= pKa, correlated with the nucleophilicity (pKa) of (2), giving slopes of 0.78 0.86 for log k2 vs. pKa plots. The plot of log k2 vs. σ for metasubstituted (1) showed a linear relationship with ρ=0.651.28. The rate of ortho-substituted (1) was smaller than that of meta-substituted (1), because of the steric hindrance of ortho-substituent in (1). The ratios, 10-3k2/k1, d exceeded unity. The above observations demonstrate N-arylcarbonylation involving a nucleonphilic attack of a free amino group on the ester carbonyl carbon in (1) and the possibility of (1) as an N-arylcarbonyl reagent of proteins.
