Synthesis, spectral study and cytotoxicity of platinum(II) complexes with 2,9-disubstituted-6-benzylaminopurines

A series of platinum(II) complexes with 2,9-disubstituted-6-benzylaminopurines has been prepared. The complexes have the following composition: cis-[Pt(Boh)2Cl2] (1), cis-[Pt(Oc)2Cl2] (2), cis-[Pt(Ros)2Cl2] (3), cis-[Pt(i-PrOc)2Cl2] (4), cis-[Pt(BohH+)2Cl2]Cl2 (5), cis-[Pt(OcH+)2Cl2]Cl2 (6), cis-[Pt(RosH+)2Cl2]Cl2 (7) and cis-[Pt(i-PrOcH+)2Cl2]Cl2 (8), where Boh = 2-(3-hydroxypropylamino)-6-benzylamino-9-isopropylpurine, Oc = 2-(2-hydroxyethylamino)-6-benzylamino-9-methylpurine, Ros = 2-(R)-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine and i-PrOc = 2-(2-hydroxyethylamino)-6-benzylamino-9-isopropylpurine. The complexes have been characterized by elemental analyses, conductivity measurements and their infrared, ES + mass (electrospray mass spectra in the positive ion mode) and NMR (1H, 13C, 15N and 195Pt) spectra. The results obtained from the physical studies, particularly from multinuclear NMR spectroscopy, show that in all the investigated complexes (1–8), two molecules of purine derivative are coordinated to platinum via the N(7) atom of the imidazole ring in a cis-configuration. The prepared compounds have been screened for their in vitro cytotoxicity against G-361 (human malignant melanoma), HOS (human osteogenic sarcoma), K-562 (human chronic myelogenous leukemia) and MCF-7 (human breast adenocarcinoma) cell lines. All complexes are significantly more active than the initial 2,9-disubstituted-6-benzylaminopurine derivatives. In the case of some tumour cell lines, IC50 values for the complexes (1, 3, 4, 5, 8) are significantly lower than those obtained for cisplatin and oxaliplatin. The best cytotoxicity was achieved for the complex (3) for which IC50 values range from 1 to 2 μM.