Protein secondary structures such as α-helices, β-sheets, and β-turns are important in inducing the three-dimensional structure and biological activity of proteins. Designing secondary structure mimics composed of short peptides has attracted much attention not only to gain fundamental insight into the factors affecting protein folding but also to develop pharmacologically useful compounds, artificial receptors, asymmetric catalysts, and new materials. In this tutorial review, we focus on molecular scaffolds employed to induce β-sheet-like structure in attached peptide chains, thereby creating highly ordered molecular structures, and discuss the versatility of these molecular scaffolds to regulate the attached peptide strands in the appropriate dimensions.

The ferrocene bearing the podand dipeptide chains, Ala-Pro-OEt, which are aligned parallel in solution by the two rigid intramolecular hydrogen bonds, manifests a novel helically ordered arrangement with one turn of 14.70 Å pitch height in the crystal packing possibly due to the intramolecular hydrogen bonds (the N–H···OC distance is 2.06 Å) and the hydrophobic interaction of the podand dipeptide chains (the distance between the nearest ferrocene units is 4.54 Å).