Conformational Studies of Phe-Rich Foldamers by VCD Spectroscopy and ab Initio Calculations

摘要

Employing VCD spectroscopy, we demonstratenthat the structural behavior of the oligomers Boc-(L-Phe-LOxd)nn-OBn is similar from n = 2 to n = 6; ab initio calculationsnfor the n = 1 case provide physical insight into thenconformational properties. Further information is gained bynIR, 1H NMR, and ECD spectroscopies. ECD spectra suggestnthe presence of different conformations between n = 1 on onenside and longer chain foldamers on the other side. VCD andnabsorption IR spectra in methanol solutions can be interpretednas indicative of a PPII structure. In the case of Boc-L-Phe-L-Oxd-OBn, VCD spectra in CCl4 and detailed DFT computationalnanalysis allow one to demonstrate that the most populated conformers exhibit backbone dihedral angles similar to those of a PPIIngeometry. This is a remarkable outcome, as we had previously demonstrated that the Boc-(L-Ala-D-Oxd)n-OBn series folds in a β-nband ribbon spiral that is a subtype of the 310 helix.