Inorganic Chemistry Chart 1. Compounds 1c−5c with Atom Numbering Schemes for NMR Spectroscopic Assignment Article the antiproliferative activity, bioavailability, etc., of the resulting complexes. The promising effects, e.g., increased solubility in physiologically relevant media and synergistic effects from metal and ligand leading to highly cytotoxic species, warrant further efforts in this area. Herein, we describe the synthesis and characterization of a series of new ruthenium arene complexes of the general formula [RuCl(η6-arene)(L)]Cl (Chart 1), with a modified arene ligand, 4-formylphenoxyacetyl-η6-benzylamide, that may be tethered to rHSA and L = 3-(1H-benzimidazol-2-yl)-1H- pyrazolo[3,4-b]pyridines (L1−L3) and indolo[3,2-d]- benzazepines (L4 and L5), which are potential Cdk inhibitors. In order to achieve targeted drug delivery and potentiate the pharmacological effects of the compounds, conjugation of the ruthenium moiety to modified rHSA was realized via hydrazone bond formation according to reported procedure.10 Interest- ingly, cleavage of the hydrazone bond under acidic conditions has been exploited for drug release in cancer cells.26,27 The complexes and their rHSA conjugates have been screened for antiproliferative activity on different human cancer cell lines, and the observed effect on the antitumor activity of tethering these organometallic compounds to rHSA has been discussed. ■ EXPERIMENTAL SECTION General Details. 3-(1H-Benzimidazol-2-yl)-1H-pyrazolo[3,4-b]- pyridine (L1),25 3-(1H-benzimidazol-2-yl)-5-bromo-1H-pyrazolo[3,4- b]pyridine (L2),25 5-bromo-3-(4-methoxymethyl-1H-benzimidazol-2- yl)-1H-pyrazolo[3,4-b]pyridine (L3),25 9-(pyridin-2-ylmethylidene)- amino-7,12-dihydroindolo[3,2-d][1]benzazepin-6(5H)-one (L4),21 9- bromo-6-(α-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L5),22 and [RuCl(μ-Cl)(η6-arene)]2 (where arene = 4-formylphenox- yacetyl-η6-benzylamide)11 were prepared according to published protocols (Schemes S1−S3 in the Supporting Informtion). Solvents (ethanol and diethyl ether) were dried using standard procedures. Syntheses of complexes were performed under an argon atmosphere using Schlenk techniques. Elemental analysis (C, H, N, Cl, Br, and S) was performed by the Microanalytical Service of the Institute of Physical Chemistry of the University of Vienna. Electrospray ionization mass spectrometry (ESI-MS) spectra were recorded on a Bruker Esquire 3000 instrument (Bruker Daltonics, Bremen, Germany) using methanolic solutions of the complexes. Values of m/z are quoted for the species with the highest natural abundance. UV−vis spectra were recorded on a Perkin-Elmer Lambda 20 UV−vis spectrophotometer with samples dissolved in methanol (1c−5c) and water (4c and 5c) over 24 h. 1H, 13C, and 15N NMR and 15N,1H HSQC, 13C,1H HSQC, 13C,1H HMBC, 1H,1H COSY, 1H,1H TOCSY, and 1H,1H ROESY NMR spectra were measured on a Bruker DPX500 (Ultrashield Magnet) in DMSO-d6 ([RuCl(μ-Cl)(η6-arene)]2, [RuCl2(η6-arene)(DMSO)], 1c−5c, and 2c−HCl), D2O (for 4c only 1H NMR), and MeOH-d4 (for 5c only 1H and 1H,1H ROESY NMR) using standard pulse programs at 500.32 (1H), 125.81 (13C), and 50.70 (15N) MHz. 1H and 13C shifts are referenced relative to the solvent signals. 2D NMR spectra for 5c were registered at an equilibrium of E/ Z isomers (for a 2-day-old DMSO-d6 solution). Synthesis of [RuCl2(η6-arene)(DMSO)]. Red crystals of [RuCl2(η6-arene)(DMSO)]·0.5H2O suitable for X-ray diffraction study have been obtained from a 1% DMSO/H2O solution of [RuCl(μ-Cl)(η6-arene)]2 upon standing at room temperature for 1 month. An upscaled synthesis of [RuCl2(η6-arene)(DMSO)] along with analytical data is given in the Supporting Information. Synthesis of [RuCl(η6-arene)(L1)]Cl (1c). [RuCl(μ-Cl)(η6-are- ne)]2·0.5H2O (149.7 mg, 0.17 mmol) and L1 (123 mg, 0.52 mmol) were heated in ethanol (25 mL) at 85 °C for 1.5 h. The solvent was evaporated to half of the initial volume, forming a brick-red precipitate that was removed by filtration and dried in vacuo at 50 °C. Yield: 172.8 mg, 75%. Anal. Calcd for C29H24Cl2N6O3Ru·0.75H2O (1c·0.75H2O) (Mr = 690.03 g mol−1): C, 50.48; H, 3.72; N, 12.18; Cl, 10.28. Found: C, 50.57; H, 3.52; N, 12.01; Cl, 10.20. ESI-MS in MeOH (positive): m/z 605 [1c − HCl − Cl]+, 641 [1c − Cl]+, 663 [1c − HCl + Na]+. ESI-MS in MeOH (negative): m/z 639 [1c − HCl − H]−. UV−vis [MeOH; λmax, nm (ε, M−1 cm−1)]: 269 (28 807), 283 (31 573), 289 (32 451), sh 333 (17 493). 1H NMR (500.32 MHz, DMSO-d6): δ 14.82 (br s, 1H, H1b), 9.88 (s, 1H, H17d), 9.12 (d, 1H, J = 6.22 Hz, H4a), 8.81 (tr, 1H, J = 6.26 Hz, H8d), 8.78 (d, 1H, J = 5.19 Hz, H6a), 8.10 (dd, 1H, J = 1.84 and 6.82 Hz, H4b), 7.84 (d, 2H, J = 8.83 Hz, H13d + H15d), 7.81 (dd, 1H, J = 1.94 and 6.10 Hz, H7b), 7.57 (dd, 1H, J = 4.62 and 8.21 Hz, H5a), 7.55−7.51 (m, 2H, H5b + H6b), 7.06 (d, 2H, J = 8.72 Hz, H12d + H16d), 6.52 (tr, 1H, J = 5.83 Hz, H2d or H4d), 6.46 (m, 2H, H2d or H4d + H1d or H5d), 6.33 (br s, 1H, H1d or 12670 dx.doi.org/10.1021/ic201801e | Inorg. Chem. 2011, 50, 12669−12679