Mn(II)-based MRI contrast agent candidate for vascular imaging.

Toxicity concerns related to Gd(III)-based magnetic resonance imaging (MRI) agents prompted an intensive research toward their replacement by complexes of essential metal ions, like Mn(II). Here, we report a macrocyclic chelate, [Mn(PC2A-BP)], which possesses high thermodynamic stability (log K-MnL = 14.86 and pMn=8.35) and kinetic inertness (t(1/2)(pH=7.4) = 286.2 h) as well as as remarkable relaxivity (r(1p) = 23.5 mM(-1) s(-1), 0.49 T, 37 degrees C) in the presence of human serum albumin, allowing a significant MRI signal intensity increase in the vasculature even at low dose (25 mu mol/kg) of the complex.