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Issue 17, 2009
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Gd(iii) complex of a monophosphinate-bis(phosphonate) DOTA analogue with a high relaxivity; Lanthanide(iii) complexes for imaging and radiotherapy of calcified tissues

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Abstract

A new phosphinic-acid DOTA-like ligand, DO3APBP, containing a geminal bis(phosphonic acid) moiety as a highly effective bone-seeking group, was synthesized in high yield. Its crystal structure was determined by X-ray analysis. Complexation with lanthanide(III) ions occurs under mild conditions (pH = 8–9, 25 °C, 2–3 h). 1H, 31P, and 17O NMR spectroscopy show that DO3APBP forms nine-coordinated lanthanide(III) complexes with one water molecule in the first coordination sphere except for Ln = Er–Lu, which have in addition a species without lanthanide(III)-bound water. Selective formation of only two diastereomers (out of four possible) suggests that the coordinated phosphinate phosphorus atom occurs exclusively in one of the enantiomeric forms. The ratio of the twisted square antiprism (TSA) and square antiprism (SA) diastereomers changes along the lanthanide series; the gadolinium(III) complex has about 35% of the TSA species. The bis(phosphonate) moiety remains free for anchoring to osseous tissue. The 1H longitudinal relaxivity of the Gd-DO3APBP complex (r1 = 7.4 s−1mM−1, 20 MHz, 25 °C, pH = 7.5) is unexpectedly high compared to that of other monohydrated chelates of similar size thanks to a significant contribution from the second hydration sphere. The water residence time τM298 is 198 ns. Further increase in the relaxivity was observed in the presence of Zn(II), Mg(II) or Ca(II) ions, due to formation of coordination polymers. Slowing down of the tumbling rate of the Gd-DO3APBP complex upon adsorption on hydroxyapatite also leads to an increase of the relaxivity (r1 = 17 s−1mM−1, 20 MHz, 25 °C, pH = 7.5).

Graphical abstract: Gd(iii) complex of a monophosphinate-bis(phosphonate) DOTA analogue with a high relaxivity; Lanthanide(iii) complexes for imaging and radiotherapy of calcified tissues

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Supplementary files

Article information


Submitted
19 Nov 2008
Accepted
25 Feb 2009
First published
20 Mar 2009

Dalton Trans., 2009, 3204-3214
Article type
Paper

Gd(III) complex of a monophosphinate-bis(phosphonate) DOTA analogue with a high relaxivity; Lanthanide(III) complexes for imaging and radiotherapy of calcified tissues

T. Vitha, V. Kubíček, J. Kotek, P. Hermann, L. Vander Elst, R. N. Muller, I. Lukeš and J. A. Peters, Dalton Trans., 2009, 3204
DOI: 10.1039/B820705D

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