A convenient synthesis of novel bifunctional prochelators for coupling to bioactive peptides for radiometal labelling

New DOTA-based bifunctional prochelators, e.g., 1-(1-carboxy-3-carbotertbutoxypropyl)-4,7,10-(carbotertbutoxymethyl)-1,4,7,10-tetraazacyclodode-cane (DOTAGA(tBu)4), (6d) for a broad application in the modification of biomolecules with metal ions were prepared. The five-step synthesis of 6d has an overall yield of about 20%. The coupling of 6d to a bioactive peptide on solid-phase was exemplified with use of a CCK-B (cholecystokinin) analogue.