Peptide foldamers composed of six-membered ring α,α-disubstituted α-amino acids with two changeable chiral acetal moieties

Abstract Chiral cyclic α,α-disubstituted α-amino acids with four chiral centers at their acetal moieties were synthesized. An X-ray crystallographic analysis of homo-chiral tripeptide with (2 R ,3 R )-butane-2,3-diol acetal moieties revealed that the tripeptide formed both ( P ) and ( M ) helical structures, and all peptide main-chain N( i )–H were intramolecularly hydrogen-bonded with the side-chain acetal –O– of the same amino acid residues ( i ). The effect of the four chiral centers in the amino acid residue on the peptide backbone helical-screw control was very weak.