pH-Dependent Conformational Switching of Amide Bonds─from Full trans to Full cis and Vice Versa.

Strategies enabling the pH-dependent conformational switching of amide bonds from trans to cis , and vice versa, are yet limited in the sense that, in a suitable pH range, one rotamer may be stabilized to a large extent while the complementary pH range only leads to a mixture of isomers. By exploiting the effects of steric demand and the interaction of the amide carbonyl with a positive charge, we herein present the first examples for reversible pH-dependent switching from full trans to full cis .