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The Ru(ii) complex fac-[RuCl(dmso-S)3(dmso-O)2][PF6] (P2) was found to be an excellent precursor for the facile preparation in high yield of half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)3(N)2][PF6] (e.g.(N)2= 1,2-diaminoethane (en, 4), trans-1,2-diaminocyclohexane (dach, 5), or 2 NH3(6)). Neutral half sandwich-type compounds of the general formula fac-[RuCl(dmso-S)3(N–O)] where N–Ois an anionic chelating ligand (e.g. N–O= picolinate (pic, 7)) are best prepared from the universal Ru(ii)-dmso precursor cis-[RuCl2(dmso)4] (P1). These complexes, that were fully characterized in solution and in the solid state, are structurally similar to the anticancer organometallic compounds [Ru(η6-arene)(chel)Cl][PF6]nbut, in place of a face-capping arene, have the fac-Ru(dmso-S)3fragment. In contrast to what observed for the corresponding arene compounds, that rapidly hydrolyze the Cl ligand upon dissolution in water, compounds 4–6are very stable and inert in aqueous solution. Probably their inertness is the reason why they showed no significant cytotoxicity against the MDA-MB-231 cancer cell line. [ABSTRACT FROM AUTHOR]

With the aim of expanding the structure-activity relationship investigation, the series of Ru(II) half sandwich coordination compounds of the type [Ru([9]aneS3)(chel)(L)](n+) previously described by us (where [9]aneS3 is the neutral face-capping ligand 1,4,7-trithiacyclononane, chel is a neutral or anonic chelating ligand, L = Cl(-) or dmso-S, n = 0-2) was extended to 1,4,7-triazacyclononane ([9]aneN3). In addition, new neutral N-N, and anionic N-O and O-O chelating ligands, i.e. dach (trans-1,2-diaminocyclohexane), pic(-) (picolinate), and acac(-) (acetylacetonate), were investigated in combination with both [9]aneS3 and [9]aneN3. Overall, ten new half-sandwich complexes were prepared and fully characterized and their chemical behaviour in aqueous solution was established. The single-crystal X-ray structures of eight of them, including the versatile precursor [Ru([9]aneN3)(dmso-S)(2)Cl]Cl (9), were also determined. The results of in vitro antiproliferative tests performed on selected compounds against MDA-MB-231 human mammary carcinoma cells confirmed that, in this series, only compounds that hydrolyse the monodentate ligand at a reasonable rate show moderate activity, provided that the chelate ligand is a hydrogen bond donor.

The conjugation of porphyrins to metal fragments is a strategy for making new compounds that are expected to combine the phototoxicity and the tumour-localization properties of the porphyrin chromophore with the cytotoxicity of the metal fragment for additive antitumour effect. We report here the preparation of new classes of porphyrin-ruthenium conjugates with potential bio-medical applications. Ruthenium was chosen because several Ru compounds have shown promising anticancer activity. The conjugation with the porphyrin moiety was accomplished either through peripheral pyridyl rings (e.g.meso-4'-tetrapyridylporphyrin, 4'TPyP) or through bpy units (e.g.meso-(p-bpy-phenyl)porphyrins, bpy(n)-PPs, n = 1-4). The number of Ru fragments attached to the porphyrins ranges from 1 to 4 and the total charge of the conjugates from -4 to +8. Different types of peripheral fragments, both Ru(III) and Ru(II), have been used: in some cases they are structurally similar to established anticancer compounds. Examples are [Na](4)[4'TPyP{trans-RuCl(4)(dmso-S)}(4)] (2), that bears four NAMI-type Ru(III) fragments, or [4'TPyP{Ru([9]aneS3)(en)}(4)][CF(3)SO(3)](8) (3) and [bpy(4)-PP{Ru([9]aneS3)(dmso-S)}(4)][CF(3)SO(3)](8) (9) (en = ethane-1,2-diamine, [9]aneS3 = 1,4,7-trithiacyclononane) that have four half-sandwich Ru(II) compounds. The Ru fragments may either contain one or more labile ligands, such as in 2 or in 9, or be coordinatively saturated and substitutionally inert, such as in 3 or in [bpy(4)-PP{Ru([12]aneS4)}(4)][CF(3)SO(3)](8) (11) ([12]aneS4 = 1,4,7,10-tetrathiacyclododecane). Most of the ruthenium-porphyrin conjugates described in this work are soluble--at least moderately--in aqueous solution and are thus suitable for biological investigations, in particular for cytotoxicity and photo-cytotoxicity tests.

The development of new metal anticancer compounds is a challenge for inorganic chemists. We have to face the fact that four decades of research in this field have only produced a small number of clinically used compounds, most often developed through serendipity rather than through rational chemical design. Nevertheless, by virtue of the wealth of knowledge acquired in these years, medicinal inorganic chemistry is probably mature for making significant steps forward and there are great expectations for future developments. With the aim of contributing to the rationalization of this field, we suggest here a categorization of metal anticancer compounds into five classes based on their mode of action: (i) the metal has a functional role, i.e. it must bind to the biological target; (ii) the metal has a structural role, i.e. it is instrumental in determining the shape of the compound and binding to the biological target occurs through non-covalent interactions; (iii) the metal is a carrier for active ligands that are delivered in vivo; (iv) the metal compound is a catalyst; and (v) the metal compound is photoactive and behaves as a photo-sensitizer. Selected examples for each category are given. The few metal anticancer drugs that are in clinical use are all believed to be functional compounds. Our classification, that is clearly focused on the metal compound and is independent from the nature of its bio-target(s)-most often still unknown-has the purpose of providing an intellectual tool that might be helpful in the rational development of new drugs.