Coumarin‐Tagged Dinuclear Trithiolato‐Bridged Ruthenium(II)⋅Arene Complexes: Photophysical Properties and Antiparasitic Activity

The synthesis, characterization, photophysical and biological properties of 13 new conjugate coumarin‐diruthenium(II)⋅arene complexes against Toxoplasma gondii are presented. For all conjugate organometallic unit/coumarins, an almost complete loss of fluorescence efficacy was observed. However, the nature of the fluorophore, the type of bonding, the presence and length of a linker between the coumarin dye and the ruthenium(II) moiety, and the number of dye units influenced their biological properties. The in vitro activity against a transgenic T. gondii strain grown in human foreskin fibroblasts (HFF) leads to IC(50) values for T. gondii β‐gal from 105 to 735 nM. Of note is that nine compounds displayed lower IC(50) than the standard drug pyrimethamine. One compound applied at its IC(50) did not affect B‐cell proliferation but had an impact on T‐cell proliferation in murine splenocyte cultures. Transmission electron microscopy of T. gondii β‐gal‐infected HFF showed that treatment predominantly affected the parasites’ mitochondrion.