α-Substitution Effects on the Ease of S→ N-Acyl Transfer in Aminothioesters

In S-acylcysteines and homocysteines, the efficacy and rate of SN-acyl transfer (5 and 6 cyclic TSs) vary with the size of S-acyl group. Conformational and quantum chemical calculations indicate that the spatial distance, b(N-C), between the terminal amine and the thioester carbon is shortened by -C(O)X (X=OH, OMe, NH2) substituents.