An improved synthesis of [125I]N-(diethylaminoethyl)-4-iodobenzamide: a potential ligand for imaging malignant melanoma.

To improve the radiolabeling yield and the specific activity of [125I]N-(2-diethylaminoethyl)-4-iodobenzamide (DAB), the aryltributyltin precursor was synthesized from the N-(2-diethylaminoethyl)-4-bromobenzamide derivative by palladium catalyzed stannylation using bis(tributyltin). The radiolabeled product, [125I]DAB, was obtained by an iododestannylation reaction in high radiochemical yields (85-94%, radiochemical purity, > 98%) using chloramine-T as an oxidizing agent. The specific activity was greater than 1600 Ci/mmol. The biodistribution studies in nude mice implanted with human malignant melanoma xenograft showed a good tumor uptake (6.14% ID/g at 1 h, 2.81% ID/g at 6 h and 0.42% ID/g at 24 h) of [125I]DAB. Unfortunately, a high uptake in the non-target organs, such as liver and lung, was found. At 1 h post-injection the activity level in liver and lung was 11.76 and 7.58% ID/g, respectively. A slow clearance of activity from liver and lung was observed at 6 h (3.43 and 0.49% ID/g). These results demonstrate that iodinated IDAB is a potential radiopharmaceutical for the management of patients with malignant melanoma.