Helicity of N,N′-diaryl-trans-1,2-diaminocyclohexane derivatives.: Implications for molecular helicity manipulations

Derivatives of trans-1,2-diaminocyclohexane (DACH), useful as chiral ligands, scaffolds and building blocks, differ in their conformation. The conformation of N,N'-diaryl-DACH derivatives was studied by the semiempirical and DFT computational methods and by exciton-coupled circular dichroism. It was found that, contrary to M-helical N,A -diimine, N,N'-diimide and N,N'-diamide derivatives, the aromatic residues in N,M-diphenyl derivatives are oriented to form a P-helix for the (R,R)-DACH absolute configuration. The helicity of the bis-aryl system is modified in the case of I-naphthyl or 2-naphthyl derivatives. Further switching of helicity has been demonstrated by either protonation or mono-N-acetylation of N,N'-diaryl DACH derivatives. (C) 2003 Published by Elsevier Ltd.