3-(3 '-fluorenyl-9 '-oxo)-L-alanine: a novel photoreactive conformationally constrained amino acid

Photoaffinity scanning of the ligand-G-protein-coupled receptor bimolecular interface is a direct approach to mapping the interactions of ligands and receptors. Such studies are an important first step toward generating an ex perimentally based model of the ligand-receptor complex. The synthesis and spectroscopic characterization of Boc-3-(3'-fluorenyl-9'-oxo)-L-alanine and 9 fluorenone-3-carboxylic acid are described. Incorporation of these two p hotophores into the parathyroid hormone (PTH) molecule yields potent agonis ts. These photoreactive analogs cross-link specifically with the recombinan t human PTH1 receptor stably expressed in human embryonic kidney cells. The availability of the 9-fluorenone (a conformationally constrained derivativ e of benzophenone, the abundantly used photophore) for photoaffinity scanni ng provides an important tool to probe the effect of conformational flexibi lity of the photophore on the selection of the cross-linking site in the ma cromolecular acceptor.