Structural investigation of "cis" and "trans" vinylogous peptides: cis-vinylog turn in folded cis-vinylogous peptides, an excellent mimic of the natural β-turn

Abstract

Various sequences of modified peptides including those containing a cis- or trans-vinylogous residue have been studied using X-ray diffraction in the solid state and 1H NMR and IR spectroscopy in solution. A cis-vinylogous residue promotes an NH to CO intramolecular H-bond, closing a nine-membered pseudocycle that stabilizes a folded moiety that we proposed to name the cis-vinylogous turn. A trans-vinylogous residue involves an extended conformation. Two consecutive vinylogous residues retain their own structural propensity: "Xaatr"-"Xaacis" or "Xaacis"-"Xaatr" sequence is singly folded, whereas "Xaacis"-"Xaacis" sequence is doubly folded. Oligo vinylogs with all-trans or all-cis or alternating cis-trans motifs could constitute new classes of foldamers. © 2005 American Chemical Society.