Abstract |
Replacing the N,N-chelating ligand 2,2'-bipyridine (bpy) in the Ir(III) pentamethylcyclopentadienyl (Cp*) complex [(η(5)-C(5)Me(5))Ir(bpy)Cl](+) (1) with the C,N-chelating ligand 2-phenylpyridine (phpy) to give [(η(5)-C(5)Me(5))Ir(phpy)Cl] (2) switches on cytotoxicity toward A2780 human ovarian cancer cells (IC(50) values of >100 μM for 1 and 10.8 μM for 2). Ir-Cl hydrolysis is rapid for both complexes (hydrolysis equilibrium reached in <5 min at 278 K). Complex 2 forms adducts with both 9-ethylguanine (9-EtG) and 9-methyladenine (9-MeA), but preferentially with 9-EtG when in competition (ca. 85% of total Ir after 24 h). The X-ray crystal structure of [(η(5)-C(5)Me(5))Ir(phpy)(9-EtG-N7)]NO(3)·1.5CH(2)Cl(2) confirms N7 binding to guanine. Two-dimensional NMR spectra show that complex 2 binds to adenine mainly through N1, consistent with density functional theory (DFT) calculations. DFT calculations indicate an interaction between the nitrogen of the NH(2) group (9-MeA) and carbons from phpy in the adenine adduct of complex 2. Calculations show that the most stable geometry of the adduct [(η(5)-C(5)Me(5))Ir(phpy)(9-EtG-N7)](+) (3b) has the C6O of 9-EtG orientated toward the pyridine ring of phpy, and for [(η(5)-C(5)Me(5))Ir(phpy)(9-MeA-N1)](+) (4(N1)a), the NH(2) group of 9-EtA is adjacent to the phenyl ring side of phpy. Complex 2 is more hydrophobic than complex 1, with log P values of 1.57 and -0.95, respectively. The strong nucleobase binding and high hydrophobicity of complex 2 probably contribute to its promising anticancer activity.
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Authors | Zhe Liu, Luca Salassa, Abraha Habtemariam, Ana M Pizarro, Guy J Clarkson, Peter J Sadler |
Journal | Inorganic chemistry
(Inorg Chem)
Vol. 50
Issue 12
Pg. 5777-83
(Jun 20 2011)
ISSN: 1520-510X [Electronic] United States |
PMID | 21618978
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Copyright | © 2011 American Chemical Society |
Chemical References |
- Antineoplastic Agents
- Ligands
- Organometallic Compounds
- Iridium
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Topics |
- Antineoplastic Agents
(chemical synthesis, chemistry, pharmacology)
- Cell Line, Tumor
- Cell Proliferation
(drug effects)
- Crystallography, X-Ray
- Dose-Response Relationship, Drug
- Drug Screening Assays, Antitumor
- Humans
- Iridium
(chemistry)
- Ligands
- Magnetic Resonance Spectroscopy
- Models, Molecular
- Molecular Conformation
- Organometallic Compounds
(chemical synthesis, chemistry, pharmacology)
- Quantum Theory
- Stereoisomerism
- Structure-Activity Relationship
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