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How to obtain Pt(IV) complexes suitable for conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]+

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Abstract

Oxidation of [Pt(II)Cl(terpy)]+ (terpy = 2,2′:6′,2′′-terpyridine) has been attempted with several oxidizing agents and under different experimental conditions in order to obtain a Pt(IV) complex suitable for the conjugation to nanovectors to be used in drug delivery targeting for anticancer therapy. The best compromise in terms of yield and purity of the final complex was obtained by microwave-assisted reaction at 70 °C in 50% aqueous H2O2 for 2 h. Under these conditions the quantitative formation of [Pt(IV)Cl(OH)2(terpy)]+ was observed. The subsequent synthetic steps were, (i) functionalization of [Pt(IV)Cl(OH)2(terpy)]+ in the axial position with succinic anhydride to obtain [Pt(IV)Cl(OH)(succinato)(terpy)]+ and (ii) reaction of the latter with nonporous silica nanoparticles (SNPs) with an external shell containing primary amino groups to obtain a nanovector able to transport the Pt(IV) antitumor prodrug in the form of a conjugate Pt-SNP. Finally, the antiproliferative activity and cell accumulation of [Pt(II)Cl(terpy)]+, [Pt(IV)Cl(OH)2(terpy)]+, and the Pt-SNP conjugate were measured on three cancer cell lines. Despite highly effective accumulation of Pt-SNP in cells, a modest increase in activity was observed with respect to the molecular species. Further experiments showed that the Pt-SNP conjugate can release [Pt(II)Cl(terpy)]+ upon reduction, but this metabolite may undergo hydrolysis, and the resulting aquo complex could coordinate once again the free amino groups of the SNPs. In the resulting tetraamine form, the Pt(II) complex conjugated to the SNPs cannot completely perform its antiproliferative activity.

Graphical abstract: How to obtain Pt(iv) complexes suitable for conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]+

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Publication details

The article was received on 10 May 2017, accepted on 11 Jul 2017 and first published on 12 Jul 2017


Article type: Paper
DOI: 10.1039/C7DT01706E
Citation: Dalton Trans., 2017, Advance Article
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    How to obtain Pt(IV) complexes suitable for conjugation to nanovectors from the oxidation of [PtCl(terpyridine)]+

    E. Gabano, E. Perin, C. Fielden, J. A. Platts, A. Gallina, B. Rangone and M. Ravera, Dalton Trans., 2017, Advance Article , DOI: 10.1039/C7DT01706E

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