Synthesis, characterization, and biodistribution of a Technetium-99m ‘3+1’ fatty acid derivative. The crystal and molecular structures of a series of oxorhenium model complexes

Abstract

The ‘3+1’ design of complexes of the {Re VO} 3+ core was exploited in the preparation of two series of compounds incorporating fatty acid components. In one case, the fatty acid subunit is attached to the monodentate ligand ‘1’ of the [ReO(tridentate)(monodentate)] complex, with the tridentate component consisting of the sulfido–dithiolate donor, {(SCH 2CH 2) 2S} 2−, and represented by the complexes [ReO{η 3-(SCH 2CH 2) 2S}{η 1-S(CH 2) 4CO 2H}] ( 1) and [ReO{η 3-(SCH 2CH 2) 2S}{η 1-S(CH 2) 10CO 2H}] ( 2). The second series exhibits the fatty acid attachment at the tridentate site, {(SCH 2CH 2) 2NR} 2−, in the complexes of the general type [ReO{η 3-(SCH 2CH 2) 2NR}{η 1-SC 6H 4X}] ( 4: R=–(CH 2) 7CH 3, X=–Cl; 5: R=–(CH 2) 7CH 3, X=–Br; 6: R=–(CH 2) 7CH 3, X=–OCH 3) and [ReO{η 3-(SCH 2CH 2) 2NR}{η 1-SCH 2C 6H 4X}] ( 7: R=–(CH 2) 7CH 3, X=Cl; 8: R=–(CH 2) 15CH 3, X=–H). Compounds 1 and 2 exhibit square-pyramidal geometry, while 4– 8 approach more closely the trigonal bipyramidal prototype. The 99mTc analogue [ 99mTcO{η 3-(SCH 2CH 2) 2N(CH 2) 15CO 2H}{η 1-SCH 2C 6H 5}] ( 9) was also prepared. Preliminary biodistribution studies in rats indicate poor heart-to-blood ratios (less than 1.0), suggesting that the complex is not a useful reagent for heart imaging.