β‐Turn structure and intramolecular interaction of tetrapeptides containing Asp and Lys

Nmr and CD studies of terminally protected tetrapeptides were carried out in aqueous and DMSO solutions to investigate the formation and stabilization of the β‐turn structure. Boc‐Gly‐Lys‐Asp‐Gly‐OMe and Boc‐Asp‐Lys‐Asp‐Gly‐OMe appear to have a tendency to adopt a β‐turn structure in aqueous solution from the CD spectra and temperature‐dependence studies of the amide proton chemical shifts. The side‐chain conformation of the Asp residue depends greatly on its ionization state but was not affected by the deprotonation of the neighboring Lys side chain. There is evidence for an intramolecular interaction between the Asp and Lys side chains of Boc‐Gly‐Lys‐Asp‐Gly‐OMe. Such an interaction can contribute to the stabilization of the β‐turn structure.