Group 6 photo-activable carbon monoxide-releasing molecules (PhotoCORMs) with 1’10-phenanthroline based ligand as potential anti-proliferative and anti-microbial agents

A new series of group 6 UV activable photoCORMs were synthesized by reacting the ligand (((1,10-phenanthroline-5-yl)imino)methyl)naphthalen-2-ol (1) with group 6 (Cr, Mo, and W) hexacarbonyl to form 2, 3, and 4, respectively. The structural elucidations of all compounds were conducted via IR, NMR, and CHN elemental analyses. The crystal structures of all the synthesized compounds were obtained and the half-life of the photoCORMs were determined by using the three-layered myoglobin solution assay. Results showed that the half-life of the compounds decreased down the group 6 in a concentration-dependent manner, with compound 2 displaying the shortest half-life (7.1 s) at 60 µM. In the absence of UV light, compounds 1 and 3 showed cytotoxicity and selectivity against human-derived colorectal adenocarcinoma HT-29 and carcinoma HCT 116, with ligand 1 being the most cytotoxic compound. Nonetheless, most compounds were inactive against bacteria and fungi when UV light is absent, while only 1 showed appreciable activity against B. cereus, B. subtilis, E. faecalis, and S. aureus. In the presence of UV light, the cytotoxicity and selectivity of photoCORMs 2, 3, and 4 were significantly elevated, with 2 and 4 demonstrating the most drastic improvement against HT-29 (from IC₅₀ ≥ 100 to 26.03 and 38.03 µM, respectively). The growth inhibitory activity of 2, 3, and 4 were also considerably enhanced in the presence of UV illumination when tested against B. cereus, B. subtilis, S. aureus, E. coli, K. pneumoniae, and S. flexneri, with compound 2 demonstrating the biggest leap among the three photoCORMs.