The six new copper(II) coordination compounds [Cu(HL¹)Cl₂] (1), [Cu(HL¹)Br₂] (2), [Cu(H₂O)(L¹)(CH₃COO)]·1.75H₂O (3), [Cu(HL²)Cl₂] (4), [Cu(HL²)Br₂] (5), [Cu(H₂O)(L²)(CH₃COO)] (6) were synthesized with 2-formyl- and 2-acetylpyridine N⁴,S-diallylisothiosemicarbazones (HL¹ and HL²). The new isothiosemicarbazones were characterized by NMR, FTIR spectroscopy, and X-ray crystallography ([H₂L²]I). All copper(II) coordination compounds were characterized by elemental analysis, FTIR spectroscopy, and molar conductivity of their 1mM methanol solutions. Furthermore, the crystal structure of complex 3 was determined using single-crystal X-ray diffraction analysis. The studied complexes manifest antibacterial and antifungal activities, that in many cases are close to the activity of medical drugs used in this area, and in some cases even exceed them. The complexes 4 and 5 showed the highest indexes of selectivity (280 and 154) and high antiproliferative activity against BxPC-3 cell lines that surpass the activity of Doxorubicin. The complexes 1–3 also manifest antioxidant activities against cation radicals ABTS^•+ that are close to that of trolox, the antioxidant agent used in medicine.

Cancer is a major disease worldwide. Therefore, scientists are in a constant search for new, more effective and selective substances, not damaging normal cells, for the treatment of this disease. The use of coordination compounds such as anticancer agents is based on the interaction between DNA and metal-based complexes. It is known that thiosemicarbazones, isothiosemicarbazones, and 3d metal complexes with them often exhibit high anticancer activity. In this work, the S-methyl group in the composition of 2-acetylpyridine 4-allyl-S-methylisothiosemicarbazone (HL¹) was replaced by an S-allyl group. As a result, 2-acetylpyridine 4,S-diallylisothiosemicarbazone (HL²) was obtained. Two novel copper(II) coordination compounds were synthesized with HL²: Cu(HL²)Cl₂ and Cu(HL²)Br₂. The inhibitory activity of these novel coordination compounds was tested and compared with the corresponding activities of previously described complexes with 2-acetylpyridine 4-allyl-S-methylisothiosemicarbazone. The inhibitory activity toward the normal MDCK cell line decreased. Their IC₅₀ values are in the range of 1.2–1.4 μM, while the corresponding complexes with HL¹ have IC₅₀ values of 0.35–1.0 μM. Therefore, the novel complexes have a lower impact on normal cells. At the same time, the inhibitory activity toward the human pancreatic cancer cell line (BxPC-3) increased 2.5–18 times. The IC₅₀ values of the novel complexes toward BxPC-3 cells are in the range of 5–8 nM. This means that the selectivity indexes (the ratio between IC₅₀ values of normal cells and cancer cells) of the novel complexes are in the range of 150–280, which is very promising for further study of these complexes as potent selective anticancer drugs.