Synthesis of DTPA analogues derived from piperidine and azepane: Potential, contrast enhancement agents for magnetic resonance imaging

Two DTPA derivatives (PIP-DTPA and AZEP-DTPA) as potential contrast enhance ment agents in MRI are synthesized. The T1 and T2 relaxivities of their cor responding Gd(III) complexes are reported. At clinically relevant field str engths, the relaxivities of the complexes are comparable to that of the con trast agent, Gd(DTPA) which is in clinical use. The serum stability of the Gd-153-labeled complexes is assessed by measuring the release of Gd-153 fro m the ligands. The radiolabeled Gd chelates are found to be kinetically sta ble in human serum for up to at least 14 days without any measurable loss o f radioactivity.