CCK8 peptide derivatized with diphenylphosphine for rhenium labelling: synthesis and molecular mechanics calculations.

A novel CCK8 derivative bearing a chelating agent at its N- end and its oxo-rhenium(V) complex have been synthesized and characterized. The chelating agent N-[N-13-(diphenylphosphino)propionyl]glycyl]cysteine (PN2S) ligand, the coordination set of which is made by the phosphorus atom of phosphine, the nitrogen atoms of the two amido groups and the sulphur atom of cysteine, has been used due to its high affinity towards the oxo-rhenium(V) moiety. Molecular modelling studies indicate that the CCK8 peptide adopts the right conformation for cholecystokinin receptor binding, and that modifications on the N-terminal side of CCK8 obtained by introducing chelating agents and its metal complexes should not affect the interaction with CCK(A) receptor.