A family of compounds with the general formula [Fe(η⁵-C₅H₅)(CO)(PPh₃)(NCR)]⁺ has been synthesized (NCR = benzonitrile (1); 4-hydroxybenzonitrile (2); 4-hydroxymethylbenzonitrile (3); 4-aminobenzonitrile (4); 4-bromobenzonitrile (5); and, 4-chlorocinnamonitrile (6)). All of the compounds were obtained in good yields and were completely characterized by standard spectroscopic and analytical techniques. Compounds 1, 4, and 5 crystallize in the monoclinc P21/c space group and packing is determined by short contacts between the phosphane phenyl rings and cyclopentadienyl (compounds 1 and 4) or π-π lateral interactions between the benzonitrile molecules (complex 5). DFT and TD-DFT calculations were performed to help in the interpretation of the experimental UV-Vis. data and assign the electronic transitions. Cytotoxicity studies in MDA-MB-231 breast and SW480 colorectal cancer-derived cell lines showed IC₅₀ values at a low micromolar range for all of the compounds in both cell lines. The determination of the selectivity index for colorectal cells (SW480 vs. NCM460, a normal colon-derived cell line) indicates that the compounds have some inherent selectivity. Further studies on the SW480 cell line demonstrated that the compounds induce cell death by apoptosis, inhibit proliferation by inhibiting the formation of colonies, and affect the actin-cytoskeleton of the cells. These results are not observed for the hydroxylated compounds 2 and 3, where an alternative mode of action might be present. Overall, the results indicate that the substituent at the nitrile-based ligand is associated to the biological activity of the compounds.

Cyclams are macrocyclic polyamines which medical interest was fueled by the therapeutic potential of a bicyclam derivative in HIV infection, inflammatory diseases, cancer and stem-cell mobilization.[1] Taking advantage of the biocompatibility, the high metal chelation stability constants and the possibility of N-functionalization of the cyclam backbone, a variety of compounds have been explored in a wide range of medicinal applications.[2] The use of cyclams and cyclam-based complexes as antimicrobial and antitumoral agents has been described in recent years. In particular, trans-disubstituted cyclam salts revealed to be active antibacterial agents against both Gram-positive and Gram-negative bacteria.[3,4] In the field of anticancer applications, several attempts are being made, mostly with CuII complexes, envisaging their use as 64/67Cu radionuclides.[5] Recently, we found that trans-disubstituted cyclam derivatives and their CuII and FeIII complexes display relevant antitumoral activity against HeLa cancer cell lines.[6] To the best of our knowledge, this is the first report on an iron-cyclam compound tested as anticancer agent. [1] De Clercq, E., Nat. Rev. Drug Discov. 2003, 2, 581–587 [2] Liang, X.; Sadler, P. J., Chem. Soc. Rev. 2004, 33, 246-266 [3] Yu, M.; Nagalingam, G.; Ellis, S.; Martinez, E.; Sintchenko, V.; Spain, M.; Rutledge, P. J.; Todd, M. H.; Triccas, J. A., J. Med. Chem. 2016, 59, 5917–5921 [4] Alves, L. G.; Pinheiro, P. F.; Feliciano, J. R.; Dâmaso, D. P.; Leitão, J. H.; Martins, A. M., Int. J. Antimicrob. Agents 2017, 49, 646-649 [5] Cai, Z.; Anderson, C. J., J. Label. Compd. Radiopharm. 2014, 57, 224–230 [6] Pilon, A.; Lorenzo, J.; Rodriguez-Calado, S.; Adão, P.; Martins, A. M.; Valente, A.; Alves, L. G., ChemMedChem, 2019, 14, 770-778