Preparation and biological evaluation of cyclopentadienyl-based 99mTc-complexes [(Cp-R)99mTc(CO)3] mimicking benzamides for malignant melanoma targeting

The biological evaluation of half-sandwich 99mTc-complexes that surrogate iodobenzamide with a high affinity for melanin tumor tissue is described. We have synthesized via retro Diels–Alder reaction two models of 99mTc complexes which possess the piano stool [Cp99mTc(CO)3] motif instead of a phenyl ring as in the original iodobenzamide 123I-N-(N-benzylpiperidin-4-yl)-2-iodobenzamide (2-IBP) and N-(2-diethylaminoethyl)-4-iodobenzamide (BZA). Diels–Alder products 2a–b (HCp-CONHR)2 (2a, R=2-diethylaminoethyl; 2b, R=benzylpiperidin-4-yl) were prepared and reacted with fac-[99mTc(H2O)3(CO)3)]+1 in water to produce the corresponding 99mTc complexes [(