Metallostar Assemblies Based on Dithiocarbamates for Use as MRI Contrast Agents.

Abstract

Two different octadentate gadolinium chelates based on DO3A and DOTAGA chelates (hydration number q = 1) have been used to prepare a series of bi-, tri-, and tetrametallic d–f mixed-metal complexes. The piperazine-based dithiocarbamate linker ensures that rotation of the gadolinium chelates is restricted, leading to enhanced relaxivity (r1) values, which increase with the overall mass and number of gadolinium units. The r1 value (at 10 MHz, 25 °C) per gadolinium unit rises from 5.0 mM–1 s–1 for the Gd-DO3A-NH2 monogadolinium chelate to 9.2 mM–1 s–1 in a trigadolinium complex with a ruthenium(III) core. Using a 1.5 T clinical scanner operating at 63.87 MHz (25 °C), an 86% increase in the relaxivity per gadolinium unit is observed for this multimetallic compound compared to clinically approved Dotarem. The gadolinium complexes based on the DOTAGA chelate also performed well at 63.87 MHz, with a relaxivity value of 9.5 mM–1 s–1 per gadolinium unit being observed for the trigadolinium d–f mixed-metal complex with a ruthenium(III) core. The versatility of dithiocarbamate coordination chemistry thus provides access to a wide range of d–f hybrids with potential for use as high-performance MRI contrast agents.