Nicotinamide‐substituted complexes as redox markers

For developing a dihydropyridine/pyridinium salt redox delivery system that could be useful for SPECT investigations by 99m Tc compounds the synthesis of a mixed-ligand complex of the long-lived isotope 99 Tc is described. The new compound bearing a pyridinium salt moiety was characterised by NMR-spectrometry and X-ray structure analysis. By reduction with sodium dithionite the corresponding 1,4-dihydropyridine complex was prepared and the stability in buffer, tissue homogenates, blood plasma and cerebrospinal fluid was investigated by UV-VIS spectrometry.