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

A series of N,N-disubstituted salicylaldehyde semicarbazones (SSCs), HOC6H4CH=N-NHCONR2, and their rhenium(I) tricarbonyl complexes, [ReBr(CO)(3)(SSC)], have been synthesised and characterised by IR and H-1 NMR spectroscopy. Crystallographic analysis of the complex [ReBr(CO)(3)(H2Bu2)] (H2Bu2 = SSC where R=Bu-o) 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 (IC50=1-24 mu M, cf. 18 mu M 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 (CD3)(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. (C) 2012 Elsevier Inc. All rights reserved.