MIXED BETA-PEPTIDES - A UNIQUE HELICAL SECONDARY STRUCTURE IN SOLUTION

beta-Hexapeptides 1-5 and a beta-dodecapeptide 6 with sequences contai ning two different types of beta-amino acids (aliphatic proteinageous side chains in the 2- or in the 3-position) have been prepared. CD (Fi g. 1) and NMR measurements indicate that, with one exception, the seco ndary structures formed by these new beta-peptides differ from those o f isomers studied previously. Detailed NMR analysis of the beta-hexape ptide 5 (with alternating beta(2),beta(3)-building blocks) and molecul ar-dynamics simulations have produced a minimum energy conformation (F ig. 2, b) which might be described as a novel irregular helix containi ng ten- and twelve-membered H-bonded rings. This demonstrates the grea t structural variability of beta-peptides, since three different helic al secondary structures have been discovered to date.