A unique double ligand-transfer reaction is described for the preparation of substituted cyclopentadienyltricarbonylrhenium complexes. In the reaction, potassium perrhenate(VII) is reduced and carbonylated by treatment with chromium trichloride and chromium hexacarbonyl to provide a proposed alkoxy carbonyl rhenium(I) intermediate. It is believed that this intermediate then undergoes a Cp ligand-transfer reaction with an acyl-substituted ferrocene to provide the corresponding (acyl-cyclopentadienyl)tricarbonylrhenium complex. A strongly coordinating solvent such as methanol is necessary to promote the reduction of perrhenate, and a carbonyl substituent conjugated to the Cp ring is necessary to activate it for transfer from iron to rhenium. This method has potential value for the synthesis of rhenium and technetium organometallic radiopharmaceuticals.
A method for labeling proteins and peptides with (methoxycarbonyl cyclopentadienyl)tricarbonyl rhenium and technetium is described. The precursors used for this labeling are conveniently produced from perrhenate and pertechnetate, respectively, using a double ligand transfer reaction. For labeling the lysine residues of the model protein bovine serum albumin, the technetium methyl ester was saponified and then transformed into its N-hydroxysuccinimidyl ester. For the labeling of the model peptides leucine enkephalin, substance P, oxytocin, and the tumor imaging/therapy candidate octreotide, the rhenium methyl ester was saponified and activated using either 1-hydoxybenzotriazole or 1-hydroxy-7-azabenzotriazole. The activation and peptide-coupling reactions were followed using reversed-phase (C18) HPLC and yields averaged approximately 70%.
Ligands for the Estrogen Receptor, Containing Cyclopentadienyltricarbonylrhenium Units.-The preparation and determination of estrogen receptor binding affinity of a series of nonsteroidal and steroidal estrogens substituted with a CpRe(CO) 3 unit is described. While this organometallic moiety interferes with estrogen receptor binding when it is tethered close to the ligand, cf. (V), those analogues in which it is attached through a 17α-ethynyl link, cf. (III), show high estrogen receptor affinity.
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