Structural Characterization of a Trinuclear Complex of Platinum(II) Containing Bridging 1-Methylcytosine Ligands. A Combined X-ray and Multinuclear NMR Study

Abstract

The dinuclear complexes cis-[(PMe3)2Pt(1-MeCy(-H))]2X2 (X = NO3- (1A), ClO4- (1B)), containing NH2-deprotonated 1-methylcytosine (1-MeCy(-H)) ligands, in aqueous or DMSO solution, at 80-degrees-C convert quantitatively into the corresponding trinuclear derivatives cis-[(PMe3)2Pt(1-MeCy(-H))]3X3(2A,B) which have been characterized in the solid state by single-crystal X-ray analysis and in solution by multinuclear (H-1, P-31, Pt-195, C-13, and N-15) NMR spectroscopy. The nitrate salt (2A) crystallizes from ethanol in the triclinic system, space group Pl. The crystals, stable only in the presence of the solvent, have the following cell dimensions: a = 13.542(5) angstrom, b = 17.352(5) angstrom, c = 20.721(6) angstrom, alpha = 113.13(2)degrees, beta = 104.30(3)degrees, gamma = 95.77(3)degrees, Z = 2. The structure, formulated as cis-[(PMe3)2Pt(1-MeCy(-H))]3(NO3)3.EtOH.H2O, was refined to R = 6.3 and R(w) = 6.3. Better structural data were obtained with the perchlorate derivative (2B), cis-[(PMe3)2Pt(1-MeCy(-H))]3(ClO4)3.2H2O, whose structure was refined to R = 4.4 and R(w) =4.9. The colorless prisms formed from aqueous solutions have the following crystallographic data: triclinic system, space group P1BAR, a = 14.634(7) angstrom, b = 14.791(9) angstrom, c = 14.980(9) angstrom, alpha = 101.93(5)degrees, beta = 103.46(5)degrees, gamma = 90.50(4)degrees, Z = 2. In both salts, the molecular structure of the cationic complex contains three cis-(PMe3)2Pt units linked to three 1-methylcytosine anions through the N(3) and N(4) atoms. The resulting 12-membered ring contains the pyrimidinic rings almost perpendicular to the plane defined by the metal atoms. Each platinum has a square-planar coordination with a Pt...Pt distance of 5.2A. The H-1, P-31, and C-13 NMR spectra indicate that the approximate S3 symmetry of the cation is maintained in solution. The compounds 1A and 2A were also characterized by N-15 NMR spectroscopy, at natural abundance. The spectroscopic data, obtained in DMSO-d6 solution, are compared with those of the derivative cis-[(PMe3)2Pt(1-MeCY)2](NO3)2 containing as ligands the neutral N(3)-bonded nucleobase. The dinuclear and trinuclear complexes exhibit very similar N-15 chemical shifts and 2J(PN) coupling constants but remarkably different from those of the mononuclear complex

Synthesis, characterization and cytotoxic properties of platinum(II) complexes containing the nucleosides adenosine and cytidine

“…At 70°C, in a few days, it converts quantitatively into the trinuclear species 1 characterized by two AB multiplets, having relative intensities of 2:1, at δ −27.01 ( 1 J PPt = 3126 Hz), 28.31 (3234 Hz) at δ −27.14 ( 1 J PPt = 3126 Hz), 28.58 (3234 Hz, with 2 J PP =24.8 Hz) ppm, respectively. The 31 P NMR parameters of the isolated complex, in DMSO-d 6 , collected in Table 1, are very similar to those of the nucleobase analogous, structurally characterized [18]. The presence of two sets of signals for the nucleoside is in line with the existence of two conformers resulting in the relative orientation, syn and anti, of the ribose groups with respect to the pyrimidinic ring.…”

“…In this field we have shown that the neutral ligands in the cisplatin analogs cis-Pt (PR 3 ) 2 Cl 2 (PR 3 = phosphines and diphosphines) play an important role in the nuclearity and reactivity of the platinum-nucleobase adducts. As an example, the reaction of the hydroxo complex cis-[L 2 Pt(μ-OH)] 2 (NO 3 ) 2 with 1-methylcytosine (1-MeCy) causes the deprotonation of the nucleobase leading to cis-[L 2 Pt{μ-1-MeCy(−H),N 3 ,N 4 }] 3 (NO 3 ) 3 when L is PMe 3 [18] and to the mononuclear complex cis-[L 2 Pt{1-MeCy(−H),N 4 } (1-MeCy,N 3 )]NO 3 with L = PPh 3 [19]. In addition, the trinuclear species is stable in solution of nitriles (MeCN, PhCN), whereas the mononuclear species reacts with the solvent to give the amidine derivatives cis-[(PPh 3 ) 2 PtNH=C(R){1-MeCy(−2H)}]NO 3 (R=Me, Ph) [20,21].…”

Cyclic Tetranuclear and Hexanuclear Palladium(II) Complexes and Their Host−guest Chemistry

“…However, the crystal structures of several other cyclic nucleobase-containing Pt(II) complexes have been obtained, for example [Pt(en)(uracilate)] 4 (NO 3 ) 4 , which has been shown to weakly bind anions as guests in aqueous solution 13,20 and Pt(II) trimers containing bridging 1-methylcytosine 21,22 or 9-methyladenine. 23 The structure of the cyclic hexamer [(PMe 3 ) 2 Pt(9-methylguanine)] 6 (NO 3 ) 6 · 18H 2 O has been found to have S 3 symmetry with the 9-methylguanines located alternately above and below the plane of the six Pt(II).…”

Pentanuclear Platinum(II) Macrocycles with Nucleobases

“…Applying them with cisconfigured platinum(ii) and palladium(ii) complexes as metal building blocks this approach leads to multinuclear complex compounds. [6,7] The metals' square-planar coordination spheres are completed by ligands, such as ethylenediamine or cis-arranged phosphanes. In the known platinum and palladium macrocycles, aromatic amine ligands are utilized very rarely.…”