Allosteric modulation of hormone release from thyroxine and corticosteroid-binding globulins.

The release of hormones from thyroxine-binding globulin (TBG) and corticosteroid-binding globulin (CBG) is regulated by movement of the reactive center loop in and out of the ß-sheet A of the molecule. To investigate how these changes are transmitted to the hormone-binding site, we developed a sensitive assay using a synthesized thyroxine fluorophore and solved the crystal structures of reactive loop cleaved TBG together with its complexes with thyroxine, the thyroxine fluorophores, furosemide, and mefenamic acid. Cleavage of the reactive loop results in its complete insertion into the ß-sheet A and a substantial but incomplete decrease in binding affinity in both TBG and CBG. We show here that the direct interaction between residue Thr(342) of the reactive loop and Tyr(241) of the hormone binding site contributes to thyroxine binding and release following reactive loop insertion. However, a much larger effect occurs allosterically due to stretching of the connecting loop to the top of the D helix (hD), as confirmed in TBG with shortening of the loop by three residues, making it insensitive to the S-to-R transition. The transmission of the changes in the hD loop to the binding pocket is seen to involve coherent movements in the s2/3B loop linked to the hD loop by Lys(243), which is, in turn, linked to the s4/5B loop, flanking the thyroxine-binding site, by Arg(378). Overall, the coordinated movements of the reactive loop, hD, and the hormone binding site allow the allosteric regulation of hormone release, as with the modulation demonstrated here in response to changes in temperature.

Natural-product-like spiroketals and fused bicyclic acetals as potential therapeutic agents for B-cell chronic lymphocytic leukaemia.

B-cell chronic lymphocytic leukaemia (CLL) is the most common form of leukaemia in the Western world for which no curative treatments are currently available. Purine nucleotide analogues and alkylating agents feature frequently in combination regimens to treat the malignant state, but their use has not led to any significant improvement in patient survival. Consequently, there still remains a need for alternative small-molecule chemotherapeutics. Natural products are an unparalleled source of drug leads, and an unending inspiration for the design of small-molecule libraries for drug discovery. The screening of focused libraries of natural-product-like spiroketal and fused bicyclic acetal small molecules against primary CLL cells has led to the identification of a small series of novel and potent cytotoxic agents towards primary CLL cells. The validation of the activity of these molecules is delineated through a series of synthesis and screening iterations, whereas preliminary mode of action studies positively indicate their ability to induce cell death via an apoptotic pathway with no evidence of necrosis to further support their potential as novel chemotherapeutic agents.

rac-(Z)-Ethyl 2-bromo-2-[(3R,5R)-3-bromo-5-methyltetrahydrofuran-2-ylidene]acetate.

In the title compound, C9H12Br2O3, a (tetrahydrofuran-2-ylidene)acetate, the double bond has the Z form. In the tetrahydrofuran group, the relative configuration of the Br atom in the 3-position and the methyl group in the 5-position is anti. The compound crystallizes with two independent molecules per asymmetric unit and, in the crystal structure, the individual molecules are linked to their symmetry-equivalent molecules by C-H...O hydrogen bonds, so forming centrosymmetric hydrogen-bonded dimers.

Multigram synthesis of well-defined extended bifunctional polyethylene glycol (PEG) chains.

A series of novel, well-defined, unsymmetrical poly(ethylene glycol) chains of the type X(OCH(2)CH(2))(n)()Y (where X = protecting group; Y = nucleofuge or a different protecting group; n = 3, 6, 9, 12, 15, 18, and 24) were prepared in high yields by applying orthogonal protecting groups. The purity of the compounds was fully verified by elemental and high-resolution mass spectrometry analyses.