52g/55Mn-Labelled CDTA-based trimeric complexes as novel bimodal PET/MR probes with high relaxivity.

trans-1,2-Diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA) labelled with a mixture of paramagnetic 55Mn(ii) and β+-emitting 52gMn(ii) offers access to bimodal Positron Emission Tomography/Magnetic Resonance (PET/MR) tracers. To enhance the number of NMR-active nuclei and simultaneously improve the longitudinal relaxivity r1, a complex composed of three CDTA units was designed. Accordingly, a functionalised tris-CDTA-1,3,5-tris-triazolobenzene was prepared and labelled with c.a. and n.c.a. 52gMn. Relaxivity measurements of the 55Mn-complex showed an enhancement of r1 of 144% in comparison to the Mn-CDTA monomer. Moreover, the trimer was equipped with an additional linker functionality suitable for conjugation with biomolecules, enabling interaction with specific molecular targets.