C 11 /C 9 Helical Folding in αβ Hybrid Peptides Containing 1-Amino-cyclohexane acetic acid (β 3, 3 -Ac 6 c).

The present study describes the solid-state conformation of ab hybrid peptides, Boc-Leu-beta(3,3)-Ac(6)c-OH, P1; Boc-Leu-beta(3,3)-Ac(6)c-Leu-beta(3,3)-Ac(6)c-OMe, P2; and Boc-Leu-beta(3,3)-Ac(6)c-Leu-beta(3,3)-Ac(6)c-Leu-OMe, P3. The dipeptide P1 adopts extended conformations, whereas tetrapeptide P2 and pentapeptide P3 favor a helical conformation stabilized by mixed types of C-11/C-9 intramolecular hydrogen bonds. In peptide P3, the amino group of beta(3,3)-Ac(6)c(2) and beta(3,3)-Ac(6)c(4) residues occupies axial orientation, whereas in P2 it occupies axial and equatorial orientations for residues beta(3,3)-Ac(6)c(2) and beta(3,3)-Ac(6)c(4), respectively. The self-assembly of P3 forms channels filled with solvent molecules that present interesting patterns.