Helical secondary structures of peptides composed of diastereomeric six-membered ring amino acids

Abstract

Two diastereoisomeric six-membered ring amino acids (1R,3R)-Ac₆c^M and (1S,3R)-Ac₆c^M were synthesized starting from (R)-3-methylcyclohexanone. Use of Bucherer-Bergs reaction stereoselectively gave (1R,3R)- Ac₆c^M, and that of Strecker reaction exclusively afforded (1S,3R)-Ac₆c^M. Homo-chiral homopeptides, up to hexapeptides, composed of (1R,3R)-Ac₆c^M or (1S,3R)-Ac₆c^M were prepared by solution-phase methods. Preferred secondary structures of two series of homo-chiral homopeptides were studied both in solution and in the crystal state.