*Article* **Conformational Preferences and Antiproliferative Activity of Peptidomimetics Containing Methyl 1** 0 **-Aminoferrocene-1-carboxylate and Turn-Forming Homo- and Heterochiral Pro-Ala Motifs**

**Monika Kovaˇcevi´c <sup>1</sup> , Mojca Caki´c Semenˇci´c ˇ <sup>1</sup> , Kristina Radoševi´c <sup>2</sup> , Krešimir Molˇcanov <sup>3</sup> , Sunˇcica Roca <sup>4</sup> , Lucija Šimunovi´c <sup>1</sup> , Ivan Kodrin 5,\* and Lidija Bariši´c 1,\***


**Abstract:** The concept of peptidomimetics is based on structural modifications of natural peptides that aim not only to mimic their 3D shape and biological function, but also to reduce their limitations. The peptidomimetic approach is used in medicinal chemistry to develop drug-like compounds that are more active and selective than natural peptides and have fewer side effects. One of the synthetic strategies for obtaining peptidomimetics involves mimicking peptide α-helices, β-sheets or turns. Turns are usually located on the protein surface where they interact with various receptors and are therefore involved in numerous biological events. Among the various synthetic tools for turn mimetic design reported so far, our group uses an approach based on the insertion of different ferrocene templates into the peptide backbone that both induce turn formation and reduce conformational flexibility. Here, we conjugated methyl 10 -aminoferrocene-carboxylate with homo- and heterochiral Pro-Ala dipeptides to investigate the turn formation potential and antiproliferative properties of the resulting peptidomimetics **2**–**5**. Detailed spectroscopic (IR, NMR, CD), X-ray and DFT studies showed that the heterochiral conjugates **2** and **3** were more suitable for the formation of β-turns. Cell viability study, clonogenic assay and cell death analysis showed the highest biological potential of homochiral peptide **4**.

**Keywords:** antiproliferative activity; chirality; conformational analysis; density functional theory (DFT); ferrocene; hydrogen bonds; peptidomimetic; X-ray
