title: Synthesis of tripeptide derivatized cyclopentadienyl complexes of technetium and rhenium as radiopharmaceutical probes.
abstract: We describe the syntheses of half-sandwich complexes of the type [(η(5)-Cp(CONH-R))M(CO)3] with M = Re or (99m)Tc. The R group represents different tri-peptides (tpe) which display high binding affinities for oligopeptide transporters PEPT2. The (99m)Tc complexes were prepared directly from [(99m)Tc(OH2)3(CO)3](+) and Diels-Alder dimerized, cyclopentadienyl derivatized peptides in water. This approach corroborates the feasibility of metal-mediated retro Diels-Alder reactions for the preparation of not only small molecules but also peptides carrying a [(η(5)-Cp)(99m)Tc(CO)3] tag. We synthesized the Diels-Alder product [(HCpCONH-tpe)2] from Thiele's acid [(η(5)-HCpCOOH)2] via double peptide coupling. The Re-complexes [(η(5)-CpCONH-tpe)Re(CO)3] were obtained by attaching [(Cp-COOH)Re(CO)3] directly to the N-terminus of peptides as received from SPPS. The authenticity of the (99m)Tc-complexes is confirmed by chromatographic comparison with the corresponding rhenium complexes, fully characterized by spectroscopic techniques.
authors.affiliation: Institute of Chemistry, University of the Punjab, Quaid-e-Azam Campus 54590, Lahore, Pakistan.
authors.forename: Qaisar
authors.initials: Q
authors.lastname: Nadeem
authors.forename: Daniel
authors.initials: D
authors.lastname: Can
authors.forename: Yunjun
authors.initials: Y
authors.lastname: Shen
authors.forename: Michael
authors.initials: M
authors.lastname: Felber
authors.forename: Zaid
authors.initials: Z
authors.lastname: Mahmood
authors.forename: Roger
authors.initials: R
authors.lastname: Alberto
mesh_terms: D003517:Cyclopentanes / Q000737:chemistry*; D008872:Microwaves; D015394:Molecular Structure; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D019275:Radiopharmaceuticals / Q000138:chemical synthesis* / Q000737:chemistry; D012211:Rhenium / Q000737:chemistry; D013667:Technetium / Q000737:chemistry
chemical_list: D003517:Cyclopentanes; D009842:Oligopeptides; D009942:Organometallic Compounds; D019275:Radiopharmaceuticals; D012211:Rhenium; D013667:Technetium