E.A. Popova, T.V. Serebryanskaya, S.I. Selivanov, M. Haukka, T.L. Panikorovsky, V.V. Gurzhiy, I. Ott, R.E. Trifonov, V.Yu. Kukushkin
“Water soluble platinum(II) complexes featuring 2-alkyl-2H-tetrazol-5-ylacetic acids: synthetic, X-ray diffraction, and solution NMR studies”
Eur. J. Inorg. Chem., 2016, 28, 4659-4667
DOI:10.1002/ejic.201600626
2-R-2H-Tetrazol-5-ylacetic acids (abbreviated as 2-R-taa; R = Me, iPr, tBu) react with K2[PtCl4] in 1 m HCl in H2O at r.t. furnishing trans-platinum(II) complexes trans-[PtCl2(2-R-taa)2] (1–3), whereas cis-isomeric species cis-[PtCl2(2-R-taa)2] (R = iPr, 4; tBu, 5) are isolated at lower temperature (4–6 °C). In the presence of EtOH in the reaction mixture, esterification of the tetrazol-5-ylacetoxy group of 2-tBu-taa leads to trans-[PtCl2(ethyl 2-tert-butyl-2H-tetrazol-5-ylacetate)2] (6). Complexes 1–6 were characterized by elemental analyses (CHN), HRESI+-MS, 1H, 13C{1H}, 195Pt{1H} NMR and IR spectroscopy, differential scanning calorimetry/thermogravimetry (DSC/TG), and X-ray diffraction (for 1·H2O, 2, 3·2H2O, 4, 5·2H2O, and 6). The generation of the tetrazole-based complexes in solution (1 m DCl in D2O, 25 °C) was studied by 1H NMR spectroscopy and HPLC-MS. The obtained data indicate the initial formation of anionic [PtCl3(2-R-taa)]– complexes that are subsequently converted into disubstituted isomeric platinum(II) species cis- and trans-[PtCl2(2-R-taa)2]. By contrast to cis- and trans-[PtCl2(2-R-taa)2] that were inactive in two human cancer models in vitro (IC50 > 100 µm), complex 6 demonstrated noticeable antiproliferative effects in HT-29 colon and MCF-7 breast carcinoma cell lines with IC50 values of 14.2 ± 1.1 and 5.8 ± 1.2 µm, respectively.