FULL PAPER Synthesis, structure, characterization and biological evaluation of 3-substituted 1-pyridin-2-ylimidazo[1,5-a] pyridine-based copper(I)–phosphine complexes for anticancer drug screening Larica Pathaw 1 | Themmila Khamrang 2 | Balasubramaniam Selvakumaran 3 | Mariappan Murali 3 | Pitchan Arul Prakash 4 | Mohamed Sultan Mohamed Jaabir 4 | Marappan Velusamy 1 1 Department of Chemistry, North-Eastern Hill University, Shillong, India 2 Department of Chemistry, C. I. College, Bishnupur, Manipur, India 3 Coordination and Bioinorganic Chemistry Research Laboratory, Department of Chemistry, National College (Autonomous), Tiruchirappalli, India 4 Department of Biotechnology and Microbiology, National College (Autonomous), Tiruchirappalli, India Correspondence Mariappan Murali, Coordination and Bioinorganic Chemistry Research Laboratory, Department of Chemistry, National College (Autonomous), Tiruchirappalli, Tamil Nadu 620001, India. Email: murali@nct.ac.in; ma66mu@gmail.com Marappan Velusamy, Department of Chemistry, North-Eastern Hill University, Shillong 793022, India. Email: mvelusamy@nehu.ac.in; mvelusamy@gmail.com Funding information Science and Engineering Research Board, Grant/Award Number: EMR/2016/007955 Copper(I) complexes of the types [Cu(N–N)(PPh 3 ) 2 ]NO 3 (LC41–LC44) and [Cu(N–N)(PPh 3 )(NO 3 )] (LC45) carrying 3-substituted 1-pyridine- 2-ylimidazo[1,5-a]pyridine (N–N) derivatives and triphenylphosphine (PPh 3 ) ligands have been prepared. The synthesized copper(I)–phosphine complexes were fully characterized by NMR, IR, ESI-MS and UV–visible spectroscopy as well as by cyclic voltammetry. Selected structures such as LC42, LC43 and LC45 were additionally analysed by single-crystal X-ray method, which show that copper(I) centre adopts a highly distorted tetrahedral geometry. The 1 H and 13 C NMR spectral data of the complexes throw light on the nature of metal–ligand bonding. They display dπ–π* metal-to-ligand charge transfer (MLCT) transition and show quasireversible Cu I /Cu II metal oxidation. Among the copper(I)–phosphine complexes, LC41–LC44 exhibit moderate cytotoxicity (IC 50 : 24 h, 67–74 μM; 48 h, 58–70 μM) against human lung epithelial adeno- carcinoma A549 cells, whereas LC45 displays the best activity (IC 50 : 24 h, 42 μM; 48 h, 34 μM) for A549 cancer cell line, which is better than that of the commercial antitumor drug cisplatin. All the complexes also displayed excel- lent selectivity by being relatively inactive against the human lung epithelial L132 normal cell line with selectivity index (SI) values ranging from 3.4 to 7.4. The complexes block cell cycle progression of A549 cells in G 0 /G 1 phase. FACSVerse analyses are suggestive of reactive oxygen species (ROS) generation and apoptotic cell death induced by the LC41, LC43 and LC45. The induction of apoptosis in A549 cells was shown by Annexin V with propidium iodide (PI) and 4 0 ,6-diamidino-2-phenylindole (DAPI) staining methods and established the ability of LC41, LC43 and LC45 to accumulate in the cell nuclei. Larica Pathaw and Themmila Khamrang contributed equally to this work. Received: 19 June 2020 Revised: 31 August 2020 Accepted: 4 September 2020 DOI: 10.1002/aoc.6025 Appl Organomet Chem. 2020;e6025. wileyonlinelibrary.com/journal/aoc © 2020 John Wiley & Sons, Ltd. 1 of 19 https://doi.org/10.1002/aoc.6025