The fac-[M(CO) 3 (PyA)(P)] and cis−trans-[M-(CO) 2 (PyA)(P) 2 ] neutral complexes (M is Re or 99m Tc), based on the mixed ligand strategy with pyrazine-2-carboxylic acid (PyAH) as the bidentate N,O and triphenylphosphine as the monodentate P ligand, are presented. Through the employment of the anhydride of pyrazine-2,3dicarboxylic acid (PyDA), the PyAH scaffold was conveniently derivatized with the model bioactive amine 1-(2-methoxyphenyl)piperazine, the active part of the 5-HT 1A antagonist WAY100635. Reaction of either PyAH or the pharmacophore-bearing PyAH ligand (L 1 H) with fac-[M(CO) 3 ] + core in water yielded the intermediate fac-[M(CO) 3 (PyA)(H 2 O)] complexes. The labile aqua ligand was easily replaced by PPh 3 to yield the fac-[Re(CO) 3 (PyA)(PPh 3 )] complexes, while in toluene under reflux, the cis− trans-[Re(CO) 2 (PyA)(PPh 3 ) 2 ] complexes were obtained. The latter complexes were alternatively obtained from mer-[Re(CO) 3 (PPh 3 ) 2 Cl] by refluxing with the PyA ligand in toluene. The analogous 99m Tc complexes were synthesized quantitatively, showing excellent stability in competition studies. The methodology described herein represents a practical procedure for the effective integration of the fac-[M(CO) 3 ] + core with amine-bearing biologically active compounds for diagnosis/therapy.
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