Twisted structure of a cyclic hexapeptide containing a combination of alternating L-Leu-D-Leu-Aib segments.

We designed and synthesized a C(2)-symmetric cyclic hexapeptide, cyclo(L-Leu-D-Leu-Aib)(2) (2), which contains L- and D-amino acids and achiral Aib residues. The conformation of 2 was analyzed in the crystalline state and in solution, which was a unique figure-eight-shaped conformation.