Controlling the helical screw sense of peptides with C ‐terminal L‐valine

One chiral L ‐valine ( L ‐Val) was inserted into the C ‐terminal position of achiral peptide segments constructed from α‐aminoisobutyric acid (Aib) and α,β‐dehydrophenylalanine (Δ Z Phe) residues. The IR, 1 H NMR and CD spectra indicated that the dominant conformations of the pentapeptide Boc‐Aib‐ΔPhe‐(Aib) 2 ‐ L ‐Val‐NH‐Bn (3) and the hexapeptide Boc‐Aib‐ΔPhe‐(Aib) 3 ‐ L ‐Val‐NH‐Bn (4) in solution were both right‐handed ( P ) 3 10 ‐helical structures. X‐ray crystallographic analyses of 3 and 4 revealed that only a right‐handed ( P ) 3 10 ‐helical structure was present in their crystalline states. The conformation of 4 was also studied by molecular‐mechanics calculations. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.