The first structural investigations were undertaken on a β-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. © 2001 Elsevier Science Ltd.
