Handedness Preferences of Heterochiral Helical Peptides Containing Homochiral Peptide Segments

A homochiral L ‐Leu‐ L ‐Leu‐Aib segment was incorporated into the N‐ or C‐termini of left‐handed ( M ) helical peptides ( D ‐Leu‐ L ‐Leu‐Aib) n . We then investigated the preferred conformations of two sets of three peptides; i.e., Boc‐ L ‐Leu‐ L ‐Leu‐Aib‐( D ‐Leu‐ L ‐Leu‐Aib) n ‐OMe ( n = 1: 1 ; 2: 2 ; 3: 3 ) and Boc‐( D ‐Leu‐ L ‐Leu‐Aib) n ‐ L ‐Leu‐ L ‐Leu‐Aib‐OMe ( n = 1: 4 ; 2: 5 ; 3: 6 ), in solution and in the crystalline state. Nonapeptide 2 and dodecapeptide 3 , each containing an N‐terminal L ‐Leu‐ L ‐Leu‐Aib segment, formed left‐handed ( M ) helices as the preferred secondary structures in solution. In the crystalline state, nonapeptide 2 folded into an ( M ) α‐helical structure. Peptides 4 – 6 , each containing a C‐terminal L ‐Leu‐ L ‐Leu‐Aib segment, formed roughly equivalent amounts of right‐handed ( P ) and ( M ) helices.