Rhenium(I) tricarbonyl complexes of salicylaldehyde semicarbazones: synthesis, crystal structures and cytotoxicity.

Abstract A series of N , N -disubstituted salicylaldehyde semicarbazones (SSCs), HOC 6 H 4 CH N-NHCONR 2 , and their rhenium(I) tricarbonyl complexes, [ReBr(CO) 3 (SSC)], have been synthesised and characterised by IR and 1 H NMR spectroscopy. Crystallographic analysis of the complex [ReBr(CO) 3 (H 2 Bu 2 )] (H 2 Bu 2  = SSC where R = Bu n ) showed that the SSC acts as a bidentate ligand via its imino nitrogen and carbonyl oxygen atoms. The [ReBr(CO) 3 (SSC)] complexes exhibit moderate to high cytotoxicities towards MOLT-4 cells (IC 50  = 1–24 μM, cf. 18 μM for cisplatin), and the majority of them are virtually non-toxic against non-cancerous human fibroblasts. Apoptotic assays of [ReBr(CO) 3 (H 2 Bnz 2 )] (Bnz = benzyl) revealed that it mediates cytotoxicity in MOLT-4 cells via apoptosis. The complex [ReBr(CO) 3 (H 2 Bnz 2 )] reacts with guanosine by proton transfer from the phenolic OH group to N(7) of guanosine. In (CD 3 ) 2 SO, [ReBr(CO) 3 (H 2 Bnz 2 )] undergoes facile conversion to the dimeric complex, [Re(CO) 3 (HBnz 2 )] 2 , via bromide dissociation.