Labeling of the neuropeptide enkephalin with functionalized tris(pyrazolyl)borate complexes: solid-phase synthesis and characterization of p-[Enk-OH]COC6H4TpPtMe3 and p-[Enk-OH]COC6H4TpMeRe(CO)3.

Bioconjugates of the neuropeptide Enkephalin (Enk = -Tyr-Gly-Gly-Phe-Leu-) labeled with organotransition metal tris-pyrazolylborate (Tp) complexes are reported. p-[Enk-OH]COC6H4TpPtMe3 and p-[Enk-OH]COC6H4Tp(Me)Re(CO)3 have been synthesized by solid-phase peptide synthesis (SPPS), purified by RP-HPLC, and characterized by ESI-mass spectrometry and 1H NMR and IR spectroscopies. p-[Enk-OH]COC6H4TpPtMe3 and p-[Enk-OH]COC6H4Tp(Me)Re(CO)3 constitute the first examples of Tp complexes employed in SPPS.