Functionalized rhenium(V) organoimido complexes as potential radiopharmaceuticals. 2. Synthesis, structural characterization, and reactivity of N-succinimidyl ester derivatives with amines

Organoimidorhenium(V) complexes were synthesized as potential labeling agen ts for biologically relevant organic amines using the preconjugate approach . The bistriphenylphosphine organoimidorhenium N-succinimidyl ester complex Cl-3(PPh3)(2)Re=N-C6H4CO2N-(COCH2)(2) (2) was synthesized and characterize d by single-crystal X-ray analysis. Complex 2 was coupled in aqueous dimeth ylformamide solvent with a series of primary and secondary amines, aminoaci ds, and a biotin-ethylenediamine derivative to give the corresponding amide complexes in good yields. These results demonstrate that the organoimido l inkage is resistant toward hydrolysis and stable in the presence of more ba sic alkylamines. An unusual oxygen atom transfer reaction was observed betw een the byproduct N-hydroxysuccinimide and triphenylphosphine ligands when dichloromethane was used as solvent. The dithiocarbamate complexes Cl[Et2NC S2](2)Re=N-C6H4CO2N(COCH2)(2) (3) and O[(Et2NCS2)(2)Re=N-C6H4-CO2N(COCH2)(2 )](2) (4) were also synthesized from 2. These complexes were unaffected by N-hydroxysuccinimide, but were not suitable for labeling due to hydrolysis of the organoimido groups under the reaction conditions.