‘Mixed’ β‐peptides: A unique helical secondary structure in solution. Preliminary communication

Abstract

β‐Hexapeptides 1–5 and a β‐dodecapeptide 6 with sequences containing two different types of β‐amino acids (aliphatic proteinageous side chains in the 2‐ or in the 3‐position) have been prepared. CD (Fig. 1) and NMR measurements indicate that, with one exception, the secondary structures formed by these new β‐peptides differ from those of isomers studied previously. Detailed NMR analysis of the β‐hexapeptide 5 (with alternating β 2,β 3‐building blocks) and molecular‐dynamics simulations have produced a minimum energy conformation (Fig. 2,b)which might be described as a novel irregular helix containing ten‐ and twelve‐membered H‐bonded rings. This demonstrates the great structural variability of β‐peptides, since three different helical secondary structures have been discovered to date.