Model peptides containing the 3-sulfanyl-norbornene amino acid, a conformationally constrained cysteine analogue effective inducer of 310-helix secondary structures

The properties of the constrained tetrasubstituted 3-sulfanylnorbornene amino acid (NRB), when inserted in Ala-Aib model peptides, were extensively studied. The conformational behaviour of these models was evaluated by theoretical calculations, spectroscopic analyses and by X-ray crystallography. Taken together, our data confirm that both (R,R,R,S)- and (S,S,S,R)-NRB enantiomers possess a strong helicogenic effect when inserted in short Ala-Aib sequences, suggesting that the rigid norbornane core has a positive effect on the ability to stabilize helical secondary structures. This information will be essential for future applications in the rational design of conformationally stable peptides targeted on protein-protein interaction (PPI) surfaces