Synthesis of a cholesterol-appended Tb–DTPA complex by combined removal of tert-Butyl protecting groups and complexation of terbium(III)

The Tb(III)-complex of a cholesterol–DTPA conjugate was prepared in a one-step procedure from the tert-Butyl-protected form of the ligand through reaction with TbCl3.6H2O and NaI in refluxing acetonitrile. The acid-labile carbamate linker that connects the chelating DTPA moiety with the cholesterol unit of the ligand stays intact under these conditions. The combination of deprotection of the ligand with terbium complexation reduces the overall number of synthetic steps required and thus increases the efficiency and overall yield of the reaction sequence.