Poly(ethylene glycol) modified Mn2+ complexes as contrast agents with a prolonged observation window in rat MRA

A novel rigid Mn2+ complex (MnL) with pyridine and pyrrolidine rings was designed and synthesized. The complex was further modified with alkyne, and conjugated to azide-terminated PEG by click chemistry. PEGylated MnL shows considerably higher relaxivity (MnL-PEG2k-MnL: r1 = 6.38 mmol−1 s−1; MnL-PEG4.6k-MnL: r1 = 5.63 mmol−1 s−1) and much longer blood circulation time than free Mn2+ complexes (MnL: r1 = 3.73 mmol−1 s−1), providing a prolonged time window to acquire longitudinal images for rat contrast enhanced magnetic resonance angiography.