C5 halogen substituted glucopyranosyl nucleosides (1-(β-D-glucopyranosyl)-5-X-uracil; X=Cl, Br, I) have been discovered as some of the most potent active site inhibitors of glycogen phosphorylase (GP), with respective K(i) values of 1.02, 3.27, and 1.94 μM. The ability of the halogen atom to form intermolecular electrostatic interactions through the σ-hole phenomenon rather than through steric effects alone forms the structural basis of their improved inhibitory potential relative to the unsubstituted 1-(β-D-glucopyranosyl)uracil (K(i) =12.39 μM), as revealed by X-ray crystallography and modeling calculations exploiting quantum mechanics methods. Good agreement was obtained between kinetics results and relative binding affinities calculated by QM/MM-PBSA methodology for various substitutions at C5. Ex vivo experiments demonstrated that the most potent derivative (X=Cl) toward purified GP has no cytotoxicity and moderate inhibitory potency at the cellular level. In accordance, ADMET property predictions were performed, and suggest decreased polar surface areas as a potential means of improving activity in the cell.

The above experimental data suggest the possible interaction between the four different receptors of Notch signaling pathway. The expression of CD26, cMET and N-methyltransferase Setmar was also changed. Finally, the stemness phenotype was changed in a different way each time, according to the receptor that was down regulated. All Notch receptors and particularly Notch-2 seem to play an important role in cancer stem cells.

In the present work, we investigated potential means to obtain neutral tricarbonyl mixed-ligand fac-[M(CO)LL] complexes (M = Re, Tc) containing the (2-hydroxyphenyl)diphenylphosphine (POH) bidentate ligand (LH) and a series of monodentate ligands (L). First, fac-[Re(CO)(PO)(HO)], 1, was synthesized by reaction of POH and [EtN][Re(CO)Br] in equimolar amounts in MeOH at room temperature. Interestingly, with excess of POH this reaction afforded fac-[Re(CO)(PO)(POH)], 2, with POH operating both as a bidentate and as a monodentate ligand. Owing to the presence of the labile aqua ligand, which can be readily replaced by various monodentate ligands, 1 was further used as a precursor to generate a small library of the desired fac-[M(CO)LL] complexes. Specifically, by reaction of triphenylphosphine (PPh), imidazole (im), pyridine (py), cyclohexyl isocyanide (cisc), and tert-butyl isocyanide (tbi), the following products were readily obtained in excellent yields (92%-95%): fac-[Re(CO)(PO)(PPh)], 3, fac-[Re(CO)(PO)(im)], 4, fac-[Re(CO)(PO)(py)], 5, fac-[Re(CO)(PO)(cisc)], 6, and fac-[Re(CO)(PO)(tbi)], 7. All compounds were fully characterized by elemental analysis, IR and NMR spectroscopies, and electrospray ionization(+) mass spectrometry. Their solid-state structure was elucidated by X-ray crystallography. Of considerable interest is the fact that the corresponding 2'-7' were easily accessible at the Tc-tracer level in quantitative yields after reaction of POH and the respective monodentate ligand L with fac-[Tc(CO)(HO)] in aqueous MeOH, as verified by comparative chromatographic methods adopting dual photo- and radiometric detection modes. The high stability displayed by all Tc complexes during histidine and cysteine challenge assays underscored the suitability of the fac-[M(CO)(PO)L] system for radiopharmaceutical development purposes.

Glycogen phosphorylase is a molecular target for the design of potential hypoglycemic agents. Structure-based design pinpointed that the 3¢-position of glucopyranose equipped with a suitable group has the potential to form interactions with enzyme's cofactor, pyridoxal 5¢-phosphate (PLP), thus enhancing the inhibitory potency. Hence, we have investigated the binding of two ligands, 1-(b-D-glucopyranosyl)5-fluorouracil (GlcFU) and its 3¢-CH 2 OH glucopyranose derivative. Both ligands were found to be low micromolar inhibitors with K i values of 7.9 and 27.1 lM, respectively. X-ray crystallography revealed that the 3¢-CH 2 OH glucopyranose substituent is indeed involved in additional molecular interactions with the PLP c-phosphate compared with GlcFU. However, it is 3.4 times less potent. To elucidate this discovery, docking followed by postdocking Quantum Mechanics/Molecular Mechanics-Poisson-Boltz-mann Surface Area (QM ⁄ MM-PBSA) binding affinity calculations were performed. While the docking predictions failed to reflect the kinetic results, the QM/MM-PBSA revealed that the desol-vation energy cost for binding of the 3¢-CH 2 OH-substituted glucopyranose derivative outweigh the enthalpy gains from the extra contacts formed. The benefits of performing postdocking calculations employing a more accurate solvation model and the QM/MM-PBSA methodology in lead optimization are therefore highlighted, specifically when the role of a highly polar ⁄ charged binding interface is significant. Glycogen phosphorylase (GP) is a key enzyme in glycogen metabolism that catalyzes the first step in the intracellular degradation of glycogen (1). A large number of compounds have been reported to bind at five distinct binding sites (1-3): the catalytic, the allosteric, the new allosteric, the inhibitor and the glycogen storage site. The efficacy of such inhibitors on blood glucose control and hepatic gly-cogen balance has been confirmed from animal studies and in vitro cell biology experiments (4-8) validating GP as an important target for structure-based inhibitor design of new hypoglycemic agents for the treatment of diabetes type 2. Furthermore, the number of patents filed by pharmaceutical and biotechnology companies targeting GP for the discovery of novel hypoglycemic agents has been steadily increasing in the last 3 years (9). Recently, we have investigated the binding of a series of 3¢-fluori-nated pyrimidine glucopyranonucleosides to GP which proved to be medium potency inhibitors with IC 50 values ranging between 6.5 mM and 46.4 lM (10). All the 3¢-glucose substituents were in the 3¢-equatorial position. The 3¢ carbon of glucose is 5 Š away from the c-phosphate of pyridoxal 5¢-phosphate (PLP) in the GPb-aD glucose complex (11), in the direction of the 3¢-axial position. Suitable sub-stituents at the 3¢-axial position have therefore the potential to form interactions with the proximal PLP c-phosphate (a mono-anion). Thus, building on our previous studies of modified nucleosides (10), we report here the synthesis, biochemical e...

The development of a Tc-radiotracer for imaging of β-amyloid (Aβ) plaques with single photon emission computed tomography (SPECT) is strongly anticipated to provide a low cost and broadly accessible diagnostic tool for Alzheimer's disease (AD). Within this framework, 2-(4'-aminophenyl)benzothiazole, known to display affinity and specificity for Aβ plaques, has been joined to the tricarbonyl-[M(CO)] (M = Re(I), Tc(I)) core through the cyclopentadienyl moiety to yield stable, neutral, and lipophilic complexes ( and , respectively). The complex was completely characterized with spectroscopic methods and was shown to selectively stain Aβ plaques on sections of human AD brain tissue. The complex displayed satisfactory initial brain uptake (0.53% ID/g at 2 min) and stability in healthy mice, while in transgenic 5xFAD mice, models for AD, a notable retention in the brain was noted (1.94% ID/g at 90 min). The results are encouraging and contribute to the effort of developing a SPECT amyloid imaging agent.