Crystal‐state 3D‐structural characterization of novel 3 10 ‐helical peptides

The crystal‐state conformations of two octapeptides, p BrBz‐( D ‐Iva) 8 ‐O t Bu ( 8I ) and Ac‐[ L ‐(αMe)Val] 8 ‐OH ( 8II ), the heptapeptide Z‐[ L ‐(αMe)Val] 7 ‐OH ( 7 ), the hexapeptide Z‐[ L ‐(αMe)Leu] 6 ‐O t Bu ( 6 ) and the tetrapeptide alkylamide Z‐(Aib) 2 ‐ L ‐Glu(OMe)‐ L ‐Ala‐ L ‐Lol ( 5 ) were assessed by x‐ray diffraction analyses. Two independent molecules are observed in the asymmetric unit of each L ‐(αMe)Val homo‐peptide. All four homo‐peptides are folded in a regular 3 10 ‐helical structure (only the C ‐terminal H‐bonded conformation of the D ‐Iva octapeptide is distorted to a type‐I β‐turn). The hydroxyl groups of the C ‐terminal carboxyl moieties of the two L ‐(αMe)Val homo‐peptides participate in an oxy‐analogue of the type‐III β‐turn conformation. While the two L ‐(αMe)Val 3 10 ‐helices are right‐handed, the D ‐Iva and L ‐(αMe)Leu helices are left‐handed. The tetrapeptide alkylamide is 3 10 ‐helical at the N ‐terminus, but it is mixed 3 10 /α‐helical at the C ‐terminus. Copyright © 2003 European Peptide Society and John Wiley & Sons, Ltd.