Single Turn Peptide Alpha Helices with Exceptional Stability in Water

Cyclic pentapeptides are not known to exist in alpha-helical conformations. CD and NMR spectra show that specific 20-membered cyclic pentapeptides, Ac-(cyclo-1,5) KxxxD-NH(2) and Ac-(cyclo-2,6)-RKxxxD-NH(2), are highly alpha-helical structures in water and independent of concentration, TFE, denaturants, and proteases. These are the smallest alpha-helical peptides in water.