Ln[DO3A-N-α-(pyrenebutanamido)propionate] complexes: optimized relaxivity and NIR optical properties

Abstract

We have proposed recently that the DO3A-N-α-(amino)propionate chelator and its amide conjugates are leads to targeted, high relaxivity, safe contrast agents for magnetic resonance imaging. In this work we illustrate further the expeditious nature and robustness of the synthetic methodologies developed by preparing the DO3A-N-(α-pyrenebutanamido)propionate chelator. Its Gd³⁺ chelate retains the optimized water exchange, high stability and inertness of the parent complex. The pyrene moiety imparts concentration-dependent self-assembly properties and aggregation-sensitive fluorescence emission to the Gd³⁺ complex. The Gd³⁺ complex displays pyrene-centred fluorescence whilst the Yb³⁺ and Nd³⁺ complexes exhibit sensitized lanthanide-centred near-infrared luminescence. The aggregated form of the complex displays high relaxivity (32 mM⁻¹ s⁻¹, 20 MHz, 25 °C) thanks to simultaneous optimization of the rotational correlation time and of the water exchange rate. The relaxivity is however still limited by chelate flexibility. This report demonstrates that the DO3A-N-(α-amino)propionate chelator is a valuable platform for constructing high relaxivity CA using simple design principles and robust chemistries accessible to most chemistry labs.