Study of Chemical Ligation Via 17-, 18- and 19-Membered Cyclic Transition States

Unprotected S-acylated cysteine isopeptides containing alpha-, beta- or gamma-amino acid units have been synthesized, and their conversion to native hexapeptides by S- to the N-terminus ligations involving 17-, 18- and 19-membered cyclic transition states have been demonstrated both experimentally and computationally to be more favorable than intermolecular cross-ligations.