Cyclized Dipeptide Model for a β -Bend

A cyclic dipeptide in which L-Ala-Gly was cyclized with ε -aminocaproic acid has been synthesized as a model for a β -bend. Its conformational properties have been examined by means of conformational energy calculations and nuclear magnetic resonance, infrared, Raman, and circular dichroism spectroscopy in various solvents. These calculations and experiments suggest that a type II β -bend exists in the Ala-Gly moiety, with an [Note: See the image of page 2512 for this formatted text] NH⋯ O==C hydrogen bond in the ε -aminocaproic acid portion of the molecule, and that the molecule adopts a unique conformation in solution. In contrast, an open-chain analog of this compound exists in solution as an ensemble of conformations but with a significant amount of a type II β -bend structure in the ensemble.