Novel synthetic strategies and methods have been developed for the synthesis of magnetic resonance imaging (MRI) contrasts.DTPA ligand

DOTA ligand and peptide dendrimer-based MRI probes with controllable structure were prepared.The third generation L-lysine dendrimers were synthesized by solution-phase synthesis method and convergent approach

and the primary amine groups on the surface of the dendrimers were protected by different groups.The ratio between Boc group and Cbz groups was 18 ∶ 6.The peptide dendrimers were selectively deprotected and reacted with DTPA or DOTA derivates in the presence of succinic anhydride to yield controllable ‘peripheral’functional dendrimer-based MRI contrast agents.The new compounds were confirmed by NMR

ESI-TOF MS and so on.The peptide dendrimer-based MRI probes possessing highly controlled structures and single molecular weight were tested at 1.5 T magnetic field in a clinical MRI scanner

and a 3-fold increase in T1 relaxivity to 12.53 Gd mmol.L-1.s-1 was noticed comparing to that of the clinical agent Gd-DTPA.The successful approach to synthesize the controllable dendrimer-based agent and the high T1 relaxivity of the agent opened an opportunity for the design of multifunctional dendritic contrasts for MRI.