Synthesis and reactions of trigonal-bipyramidal rhenium and technetium complexes with a tripodal, tetradentate NS3 ligand

Synthesis and Binding Affinities of Novel Re-Containing 7alpha-Substituted Estradiol Complexes: Models for Breast Cancer Imaging Agents

The diagnosis and staging of breast cancer could be improved by the development of imaging radiopharmaceuticals that provide a noninvasive determination of the estrogen receptor status in the tumor cells. Toward this goal, we have synthesized a number of novel Re-containing 7alpha-substituted estradiol complexes. The introduction of the 7alpha side chain involves the alkylation of tetrahydropyranyloxy-protected 6-keto estradiol. The methods used to introduce the rhenium metal involve "3 + 1" and "4 + 1" mixed ligand complexes (2a-c and 5, respectively), tricarbonyl dithioether complexes (3), and the cyclopentadienyltricarbonylmetal organometallic system (4ab, 6, 7). These complexes showed binding affinities for the estrogen receptor (as high as 45% for the "3 + 1" complex 2c) when compared to the native ligand estradiol. The polarity of some complexes (4ab) was modified to improve biodistribution properties by introducing (poly)ether linkages into the 7alpha side chain (6, 7). These complexes provide a further refinement of our understanding of ligand structure-binding affinity correlations for the estrogen receptor, and they furnish the synthetic groundwork for the synthesis of the analogous Tc-99m complexes for evaluation as breast tumor imaging agents.

Synthesis of novel progestin-rhenium conjugates as potential ligands for the progesterone receptor

To assist in the development of technetium-based radiopharmaceuticals that are useful for the diagnostic imaging of steroid receptor-positive breast tumors, we have synthesized a series of small-sized metal chelates according to 'n + 1' mixed-ligand, thioether-carbonyl and organometallic designs. In these preliminary investigations, rhenium was used as a model for the radioactive technetium. The metal chelates contain the rhenium metal in several oxidation states, being + 5, + 3, and + 1, and they were attached to 21-substituted progesterone derivatives. A competitive receptor-binding assay (rat uterine cytosol, 0 degrees C) was used to determine the binding affinity of these conjugates for the progesterone receptor. The highest affinity of 9% (RU5020 = 100%) was obtained with a '3 + 1' mixed-ligand complex, containing a NMe group as the central donor atom in the tridentate ligand part. This value reflects a relative binding affinity of 75% compared with the parent steroid progesterone.

Complexes of Multifunctional Phosphorus Ligands. Rhenium(V) Complexes of the Multidentate Phenoxyphosphine Ligands Bis(o-trimethylsilyloxyphenyl)phenylphosphine and Tris(o-trimethylsilyloxyphenyl)phosphine. Stepwise Elimination of Me(3)SiX (X = Cl, OEt) from the Metal-Ligand System

The silylated aryloxo ligands bis(o-silyloxyphenyl)phenylphosphine (abbreviated PhP{OT}(2)) and tris(o-trimethylsilyloxyphenyl)phosphine (abbreviated P{OT}(3), where T = Me(3)Si) were prepared. Complexation reactions with O=ReCl(2)(OEt)(PPh(3))(2) and O=ReCl(3)(PPh(3))(2) proceed by displacement of one PPh(3) and the subsequent stepwise replacement of the OEt and/or Cl substituents. The new complex Re(O)Cl(2)[kappa(2)-(P,O)-(PhP{O}{OT})](PPh(3)), formed by elimination of Me(3)SiOEt, exists in diastereomeric cis and trans forms. Elimination of a second equivalent of Me(3)SiCl gives Re(O)Cl[kappa(3)-(P,O,O)-(PhP{O}(2))](PPh(3)). Similarly P{OT}(3) converts Re(O)Cl(2)(OEt)(PPh(3))(2) to ReOCl(2)[kappa(2)-(P,O)-(P{O}{OT}(2))](PPh(3)) (5) (structurally characterized as 5.0.875CH(2)Cl(2)): crystal data; triclinic P&onemacr;, a = 14.302(4) Å, b = 18.734(2) Å, c = 17.639(4) Å, alpha = 80.950(12) degrees, beta = 80.12(2) degrees, gamma = 81.76(2) degrees, Z = 4. Final R(1) and wR(2) values are 0.0852 and 0.1525, respectively on F(o)(2) > 2sigma(F(o)(2)) data (or 0.1948 and 0.2019 on all data). The phenoxy phosphine ligand in 5 is bound via P and one O to Re. The P atoms are mutually cis to each other and to the terminal oxygen on Re. Two ortho-trimethylsiloxy substituted phenyl rings dangle from the coordinated phosphorus atom. Complex 5 can be converted to Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OT})](PPh(3)) (6) by treatment with PPN(+) Cl(-) and 6 was also obtained by direct reaction of Re(O)Cl(3)(PPh(3))(2) with P{OT}(3) at higher temperatures. The complex 6 has been structurally characterized: crystal data triclinic, P&onemacr;, a = 10.1509(6) Å, b = 12.1123(8) Å, c = 16.2142(14) Å, alpha = 97.851(7) degrees, beta = 94.852(7) degrees, gamma = 96.889(6) degrees, Z = 2. Final R(1) and wR(2) values were 0.0303 and 0.0721 on F(o)(2) > 2sigma(F(o)(2)) data (or 0.0348 and 0.0742 on all data). The phenoxyphosphine ligand in 6 is bound facially to Re through P and two of the phenoxy oxygens. The Ph(3)P group and terminal oxygen atoms are cis to the oxygen atoms of the phenoxy ligands and the Cl lies trans to P. One trimethylsiloxyphenol group dangles. Careful hydrolysis of 6 gave Re(O)Cl[kappa(3)-(P,O,O)-(P{O}(2){OH})](PPh(3)) which was also formed during complexation reactions in moist solvent. Solution (31)P{(1)H} NMR demonstrated cis- or trans-(P,P) geometry for the complexes, which was confirmed in the two aforementioned cases by structure determinations.

Synthesis and binding affinities of new 17 alpha-substituted estradiol-rhenium "n + 1" mixed-ligand and thioether-carbonyl complexes

The development of technetium and rhenium-based radiotracers for the steroid receptor system requires the use of suitable donor groups on the steroid to provide stable binding sites for the metal. Previous approaches have mainly exploited methods involving various N- and S-coordinating chelate systems or organometallic complexes. In this work, we have prepared several novel chelate systems attached to a series of 17 alpha-substituted estradiol derivatives and examined their binding to the estrogen receptor (ER). The neutral "n + 1" mixed-ligand and dithioether-carbonyl complexes that we prepared contain the metal in three oxidation states, +5, +3 or +1, attached to a 17 alpha-substituted estradiol derivative through a thiol group, an isocyanide group, or a dithioether unit, respectively. In our preliminary investigations, we used rhenium as a nonradioactive analog of the radionuclide technetium. All complexes synthesized were evaluated in a competitive radiometric receptor binding assay at 0 degree C and 25 degrees C to determine their relative binding affinities (RBA) to the ER (relative to 3,17 beta-estradiol, RBA = 100%). The complexes show binding affinities up to 23.4% at 0 degree C and 14.1% at 25 degrees C.