Synthesis and conformational characterization in the solid state of peptides consisting of L ‐phenylalanyl‐ L ‐phenylalanylglycyl and L ‐phenylalanyl‐ L ‐leucylglycyl residues

Two series of peptides containing L‐phenylalanine, Nps‐(L‐Phe‐L‐Phe‐Gly)n‐OEt (n = 1–6) and Nps‐(L‐Phe‐L‐Leu‐Gly)n‐OEt (n = 1–7), were prepared by the fragment‐condensation method using the tripeptide N‐hydroxysuccinimide esters. Conformational characterization of these peptides in the solid state was performed by ir spectroscopy and x‐ray powder diffraction measurement. The peptides Nps‐(L‐Phe‐L‐Phe‐Gly)n‐OEt take the β‐structure, but the pentadecapeptide and higher peptides of Nps‐(L‐Phe‐L‐Leu‐Gly)n‐OEt form the α‐helix, although the lower homologs take the β‐structure.