Disodium bis(o-chloranilato)uranyl(VI) hexahydrate

A Redox-Innocent Uranium(IV)-Quinoid Metal-Organic Framework

Quinoid-based ligands constitute the most common class of redox-active ligands used to construct electrically conductive and magnetic metal-organic frameworks (MOFs). Whereas this chemistry is intensively explored for transition-metal and lanthanide ions, any related actinide compound has not received attention. In particular, the MOF chemistry of actinide ions in the lower oxidation states is underexplored. We herein report the synthesis, and structural and physical property characterization of a uranium(IV) quinoid-based MOF, [U(Cl₂dhbq)₂(H₂O)₂]·4H₂O (1, Cl₂dhbq^2- = deprotonated 2,5-dichloro-3,6-dihydroxybenzoquinone). 1 is a rare example of a U(IV)-based coordination solid and the first material to incorporate bona fide reducible bridging ligands. Despite the anticipated thermodynamic driving force, no indications of valence tautomerism are evident from magnetometry, near-IR spectroscopy, and X-band electron paramagnetic resonance measurements. These initial results suggest that reduction potentials alone are insufficient as guidelines for the prediction of the occurrence of electron transfer in uranium-quinoid-based materials.

Antimineralocorticoid 11beta-substituted spirolactones exhibit androgen receptor agonistic activity: a structure function study

In humans, spironolactone and mespirenone are well known antimineralocorticoids without C-11beta substituents. These compounds display antagonist properties by acting through the human androgen receptor (hAR). In contrast, we demonstrate here that synthetic mineralocorticoid antagonists bearing hydrophobic C-11beta substituents and C-17gamma-lactone are potent hAR agonists in vitro. The three-dimensional construction of both the ligand binding domain (LBD) of the hAR and the human mineralocorticoid receptor (hMR), based on the crystal structure of the LBD of the human progesterone receptor, revealed not only that the interactions with the steroidal A- and D-rings seemed to be crucial for stabilization of active hMR or hAR conformation, but that other steroidal substitutions could influence the agonist versus antagonist activity of ligands. The docking of synthetic compounds bearing C-11beta hydrophobic substituents within the ligand binding pocket of hAR demonstrated that precise positions of the steroid, such as C-11 and C-17, are in close contact with some residues on the receptor, C-11 with Gly 708 and C-17 with Asn705 and Thr877. These contacts are crucial for the stabilization of the active receptor conformation. Mutation of Asn705 by alanine altered the 11beta-substituted spirolactone-mediated trans-activation function of hAR, suggesting an anchoring of the C-17-lactone carbonyl group (C-22) with this residue. The stabilizing effect of the H12 helix in its active conformation is also induced by hydrophobic contacts between the Gly708 and C-11beta substituents, as recently observed with the A773G-hMR mutant in the presence of similar drugs. The study of the role of these substituents suggests efficient new directions for the drug design of selective androgen agonists.

A single amino acid mutation of ala-773 in the mineralocorticoid receptor confers agonist properties to 11beta-substituted spirolactones

Sequence analysis revealed a strong homology between the ligand-binding domain (LBD) of the human mineralocorticoid receptor (hMR) and glucocorticoid receptor (hGR). Nevertheless, steroids with bulky C11-substituents bind to hGR, unlike hMR. In this report, a mutant hMR, in which the residue Ala-773 facing the C11 steroid position was replaced by a glycine (A773G), was assayed for its capacity to bind steroids, to interact with receptor coactivators, and to stimulate transcription. The capacity of A773G to bind aldosterone and C11-substituted spirolactones was the same as that of the wild-type receptor. The agonist properties of aldosterone, as well as the antagonist feature of compounds bearing a 11beta-allenyl group and a C17-ketone function, remain unchanged. In contrast, C11-substituted steroids with a 17gamma-lactonic ring displayed antagonist properties with hMR and acted as potent agonists with A773G. An agonist-dependent hMR interaction with SRC-1 was observed for both the wild-type and the mutant receptors. The hMR activation process is discussed in the light of the hMR-LBD homology model based on the structural data of the human progesterone receptor LBD.