Some Cyclic Oligopeptide with S2n Symmetry

Some cyclic oligopeptides formed by an equal number of alternating D‐ and L‐amino‐acid residues have been synthesized by using the hydrochloride of the open‐chain peptide acid as precursor and the mixed‐anhydride condensation method. The cyclic oligopeptides (tetra‐, hexa‐, and octavaline, hexaleucine, and hexaphenylalanine) form very stable H‐bonded structures (IR‐amide band at 3270–3290 cm−1) which are insoluble in common organic solvents. In CF3COOH/CDCI3 (25°), they yield 1H‐NMR spectra snowing the expected equivalency of the various amino‐acid residues.