Intramolecular acid-catalyzed amide isomerization in aqueous solution.

[reaction: see text] We report for the first time that stoichiometric and even catalytic quantities of weak acids in aqueous solution can very efficiently catalyze amide isomerization in a carefully designed system in which a proton donor is situated so that intramolecular hydrogen bonding to the amide nitrogen is highly favored. Our results provide the first experimental verification that hydrogen bond donation to the amide nitrogen by charged proton donors may play a very significant role in the enzymatic catalysis of amide isomerization.