The paullones are known as inhibitors of cyclin-dependent kinases and glycogen synthase kinase-3. However, their low aqueous solubility and bioavailability impeded their medicinal application. To overcome these problems, we developed paullone-based organic ligands and prepared organometallic complexes of the general formula [M II Cl(η 6 -p-cymene)HL]Cl (1, HL ) HL 1 ; 2, HL ) HL 2 ; a, M ) Ru; b, M ) Os). The compounds have been characterized by electrospray ionization mass spectrometry, IR, UV-vis, NMR spectroscopy, X-ray diffraction, conductivity measurements, and cyclic voltammetry. In addition, their antiproliferative activity in three human cancer cell lines has been assayed. The IC 50 values (in the submicromolar to very low micromolar concentration range) indicate their high antiproliferative activity in all three cell lines, making them potential candidates for further development as antitumor drugs. The hydrolysis behavior and reactivity of 1 and 2 toward 5′-GMP are also reported.

Paullones constitute a class of potent cyclin-dependent kinase inhibitors. To overcome the insufficient solubility and bioavailability, which hamper their potential medical application, we aim at the development of metal-based derivatives. Two types of paullone ligands, L (1) - L (3) and L (4) , with different locations of metal-binding sites, were prepared. They were found to form organometallic complexes of the general formula [M (II)Cl(eta (6)- p-cymene)L]Cl ( 1- 4, L = L (1) - L (4) ; a, M = Ru; b, M = Os). The complexes were characterized by X-ray crystallography, one- and two-dimensional NMR spectroscopy and other physical methods. Complexes 1- 3, with a coordinated amidine unit, were found to undergo E/ Z isomerization in solution. The reaction was studied by NMR spectroscopy, and activation parameters Delta H (double dagger) and Delta S (double dagger) were determined. Antiproliferative activity in the low micromolar range was observed in vitro in three human cancer cell lines by means of MTT assays. (3)H-Thymidine incorporation assays revealed the compounds to lower the rate of DNA synthesis, and flow cytometric analyses showed cell cycle arrest mainly in G 0/ G 1 phase.

Two novel paullone derivatives, namely, 6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L1) and 9-bromo-6-(alpha-picolylamino)-7,12-dihydroindolo[3,2-d][1]benzazepine (L2), have been prepared. The reaction of cis-[RuCl2(DMSO)4] (DMSO=dimethyl sulfoxide) with L1 and L2 in a 1:1 molar ratio in dry ethanol at 50 degrees C afforded the complexes trans-[RuIICl2(DMSO)2L1] (1a) and trans-[RuIICl2(DMSO)2L2] (1b) in 26 and 30% yield, respectively. The reaction carried out from the same starting compounds in a 1:2 molar ratio at 75 degrees C led to the formation of [RuIICl(DMSO)(L1)2]Cl (2a) and [RuIICl(DMSO)(L2)2]Cl (2b) in 16 and 23% yield, correspondingly. The products were characterized by elemental analysis, one- and two-dimensional NMR spectroscopy, electrospray ionization mass spectrometry, IR spectroscopy, electronic spectra, cyclic voltammetry, and X-ray crystallography (L1, L2, 1a, and 2b). Complexes 2a and 2b exhibit remarkable antiproliferative activity in three human carcinoma cell lines, A549 (non-small cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon carcinoma). The novel complexes show an intercalative mode of interaction with DNA, which may render them attractive alternatives to metal compounds with a coordinative mode of interaction.

Reaction of the antitumor complex trans-[Ru(III)Cl4(Hind)2]- (Hind = indazole) with an excess of dimethyl sulfoxide (dmso) in acetone afforded the complex trans,trans,trans-[Ru(II)Cl2(dmso)2(Hind)2] (1). Two other isomeric compounds trans,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (2) and cis,cis,cis-[Ru(II)Cl2(dmso)2(Hind)2] (3) have been obtained on refluxing cis-[Ru(II)Cl(2)(dmso)(4)] with 2 equiv. of indazole in ethanol and methanol, respectively. Isomers 1 and 2 react with acetonitrile yielding the complexes trans-[Ru(II)Cl2(dmso)(Hind){HN=C(Me)ind}].CH3CN (4.CH3CN) and trans,cis-[Ru(II)Cl2(dmso)2{HN=C(Me)ind}].H2O (5.H2O), respectively, containing a cyclic amidine ligand resulting from insertion of the acetonitrile C triple bond N group in the N1-H bond of the N2-coordinated indazole ligand in the nomenclature used for 1H-indazole. These are the first examples of the metal-assisted iminoacylation of indazole. The products isolated have been characterized by elemental analysis, IR spectroscopy, UV-vis spectroscopy, electrospray mass-spectrometry, thermogravimetry, differential scanning calorimetry, 1H NMR spectroscopy, and solid-state 13C CP MAS NMR spectroscopy. The isomeric structures of 1-3 and the presence of a chelating amidine ligand in 4 and 5 have been confirmed by X-ray crystallography. The electrochemical behavior of 1-5 and the formation of 5 have been studied by cyclic voltammetry.

In an attempt to combine the ability of indolobenzazepines (paullones) to inhibit cyclin-dependent kinases (Cdks) and that of platinum-group metal ions to interact with proteins and DNA, ruthenium(II) and osmium(II) arene complexes with paullones were prepared, expecting synergies and an increase of solubility of paullones. Complexes with the general formula [MIICl(η6-p-cymene)L]Cl, where M = Ru (1, 3) or Os (2, 4), and L = L1 (1, 2) or L2 (3, 4), L1 = N-(9-bromo-7,12-dihydroindolo[3,2-d][1]-benzazepin-6(5H)-yliden-N′-(2-hydroxybenzylidene)azine and L2 = N-(9-bromo-7,12-dihydroindolo[3,2-d][1]benzazepin-6-yl)-N′-[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl-methylene]azinium chloride (L2*HCl), were now investigated regarding cytotoxicity and accumulation in cancer cells, impact on the cell cycle, capacity of inhibiting DNA synthesis and inducing apoptosis as well as their ability to inhibit Cdk activity. The MTT (3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide) assay yielded IC50 values in the nanomolar to low micromolar range. In accordance with cytotoxicity data, the BrdU assay showed that 1 is the most and 4 the least effective of these compounds regarding inhibition of DNA synthesis. Effects on the cell cycle are minor, although concentration-dependent inhibition of Cdk2/cyclin E activity was observed in cell-free experiments. Induction of apoptosis is most pronounced for complex 1, accompanied by a low fraction of necrotic cells, as observed by annexin V–fluorescein isothiocyanate/propidium iodide staining and flow cytometric analysis.