Synthesis and structural identification of fluorine-18 labeled parathyroid hormone.

Parathyroid hormone (PTH) is an 84 amino acid peptide hormone that plays a key role in bone and mineral metabolism. The biological actions of PTH are mediated via the N-terminal PTH(1-34) fragment, serving as the PTH receptor-binding sequence, and which is therefore used clinically to treat conditions of low bone mass such as osteoporosis. In this study, PTH(1-34) was conjugated with non-radioactive (stable F isotope) N-succinimidyl 4-fluorobenzoate (SFB) leading to three isomeric mono-fluorobenzoated (FBz) PTH followed by Liquid chromatography-Tandem mass spectrometry (LC-MS/MS) assisted structural identification. Corresponding [(18)F]SFB-labeled PTH derivatives were prepared respectively and the Lys(13) site-specific labeled [(18)F]FBz PTH was isolated by HPLC with radiochemical purity >99% and specific activity of 2.78 GBq/µmol, suitable for future application with in vivo pharmacokinetic/pharmacodynamic studies of PTH, using preclinical Positron Emission Tomography Computed Tomography (PET/CT) imaging.