10-Helical conformations in oxetane β-amino acid hexamers

The first structural investigations were undertaken on a P-hexapeptide 7 in which the peptide backbone is constrained by cis-substituted oxetane rings. Detailed NMR studies in CDCl3 and C6D6 together with molecular mechanics conformational analysis identify a well-defined left-handed helical structure stabilised by 10-membered hydrogen-bonded rings. Comparison with two related hexapeptides 8 and 9 suggests a similar structural preference for these systems. (C) 2001 Elsevier Science Ltd. All rights reserved.