In vitro studies of 3-hydroxy-4-pyridinones and their glycosylated derivatives as potential agents for Alzheimer's disease.

Glycosides of 3-hydroxy-4-pyridinones were synthesized and characterized by mass spectrometry, elemental analysis, (1)H and (13)C NMR spectroscopy, and in one case by X-ray crystallography. The Cu(2+) complex of a novel 3-hydroxy-4-pyridinone was synthesized and characterized by IR and X-ray crystallography, showing the ability of these compounds to chelate potentially toxic metal ions. An MTT cytotoxicity assay of a selected glycosylated compound showed a relatively low toxicity of IC(50) = 570 +/- 90 microM in a human breast cancer cell line. The pyridinone glycosides could be cleaved by a broad specificity beta-glycosidase, Agrobacterium sp.beta-glucosidase, and for one compound k(cat) and K(m) were determined to be 19.8 s(-1) and 1.52 mM, respectively. Trolox Equivalent Antioxidant Capacity (TEAC) values were determined for the free pyridinones, indicating the good antioxidant properties of these compounds. Metal-Abeta(1-40) aggregates with zinc and copper were resolubilized by the non-glycosylated pyridinone ligands.

Glycosylated tetrahydrosalens as multifunctional molecules for Alzheimer's therapy.

The tetrahydrosalens N,N'-bis(2-hydroxybenzyl)-ethane-1,2-diamine ((2)(1)), N,N'-bis(2-hydroxybenzyl)-(-)-1,2-cyclohexane-(1R,2R)-diamine ((2)(2)), N,N'-bis(2-hydroxybenzyl)-N,N'-dimethyl-ethane-1,2-diamine ((2)(3)), N,N'-bis(2-hydroxybenzyl)-N,N'-dibenzyl-ethane-1,2-diamine ((2)(4)), and N,N'-bis(2-(4-tert-butyl)hydroxybenzyl)-ethane-1,2-diamine ((2)(5)), as well as their prodrug glycosylated forms, (1-5), have been prepared and evaluated in vitro for their potential use as Alzheimer's disease (AD) therapeutics. Dysfunctional interactions of metal ions, especially those of Cu, Zn, and Fe, with the amyloid-beta (Abeta) peptide are hypothesised to play an important role in the aetiology of AD, and disruption of these aberrant metal-peptide interactions via chelation therapy holds considerable promise as a therapeutic strategy. Tetrahydrosalens such as (2)(1-5) have a significant affinity for metal ions, and thus should be able to compete with the Abeta peptide for Cu, Zn, and Fe in the brain. This activity was assayed in vitrovia a turbidity assay; (2)(1) and (2)(3) were found to attenuate Abeta(1-40) aggregation after exposure to Cu(2+) and Zn(2+). In addition, (2)(1-5) were determined to be potent antioxidants on the basis of an in vitro antioxidant assay. (1-5) were prepared as metal binding prodrugs; glycosylation is intended to prevent systemic metal binding, improve solubility, and enhance brain uptake. Enzymatic (beta-glucosidase) deprotection of the carbohydrate moieties was facile, with the exception of (4), demonstrating the general feasibility of this prodrug approach. Finally, a representative prodrug, (3), was determined to be non-toxic over a large concentration range in a cell viability assay.

Glucosamine conjugates bearing N,N,O-donors: potential imaging agents utilizing the [M(CO)3]+ core (M = Re, Tc).

The design rationale, synthesis and radiolabeling evaluation of four glucosamine conjugated ligands for the [(99m)Tc(CO)(3)](+) core is described. The capability to bind the tricarbonyl core is initially demonstrated using the cold surrogate [Re(CO)(3)](+). The four compounds are competent chelates in binding [(99m)Tc(CO)(3)](+) as labeling studies show, with yields ranging from 79 to 96% and the resulting complexes showing stability in the presence of competing chelates for 24 h at 37 degrees C. The rhenium complexes were tested for hexokinase-catalysed phosphorylation, and the technetium complexes were tested for GLUT-1 mediated cell uptake--they showed a small amount of uptake but it was not glucose dependent, suggesting that it was not via the GLUT-1 transporters.

Long-chain rhenium and technetium glucosamine conjugates.

A series of five glucosamine-conjugated organometallic complexes of the tricarbonyl cores of technetium-99m and rhenium were made. Glucosamine was derivatized at the C-2 nitrogen with long chain alkyl spacers linked to either pyridyl-tert-nitrogen-phenol tridentate chelates or cyclopentadienyl ligating groups. The metal complexes of the tridentate ligands were formed by refluxing with [Re(CO)(3)(H(2)O)(3)]Br, or with a base and [(99m)Tc(CO)(3)(H(2)O)(3)](+). These ligands were found to be competent chelates in binding the [(99m)Tc(CO)(3)](+) core as radiolabeling yields ranged from 87 to 93% and the resulting complexes are stable to cysteine and histidine challenges for 24 h. The cyclopentadienyl analogues were formed using a double ligand transfer reaction for the rhenium complexes and a single ligand transfer for the technetium-99m complexes. All five rhenium complexes were tested as substrates of hexokinase; two of these complexes were tested as hexokinase inhibitors and they were found to be competent inhibitors, suggesting that they may be able to interact with hexokinase. MTT cytotoxicity studies were performed and the complexes tested were found to be non-toxic to the concentrations tested (100 microM or 1 mM). GLUT-1 mediated cell uptake studies were performed on all five technetium-99m complexes, and their cell entry was found to parallel their lipophilicities, suggesting that cellular uptake is by passive diffusion and is not mediated by GLUT-1.

99m-Technetium carbohydrate conjugates as potential agents in molecular imaging.

This feature article covers recent reports of work towards the development of (99m)Tc-carbohydrate based agents for use in SPECT imaging, particularly of cancerous tissue. An outline of some of the key biological functions and coordination chemistry of carbohydrates is given, along with an introduction to bioconjugation and molecular imaging. Technetium coordination chemistry and the subset of this involving bioconjugates are discussed before moving into the focus of the article: glycoconjugates of (99m)Tc(v) and the more recently developed [(99m)Tc(I)(CO)(3)](+). Significant work in the last decade has featured the very attractive [(99m)Tc(CO)(3)](+) core, and the ligand sets designed for this core are discussed in detail.

Pyridine-tert-nitrogen-phenol ligands: N,N,O-Type tripodal chelates for the [M(CO)3]+ core (M = Re, Tc).

The design rationale, synthesis, and preliminary radiolabeling evaluation of new N,N,O-type pyridyl- tert-nitrogen-phenol ligands for the [M(CO) 3] (+) core, where M = (99m)Tc or Re, are described. The capability of the ligands to bind this technetium core is initially demonstrated by using the cold surrogate [Re(CO) 3] (+). NMR studies of the relevant rhenium tricarbonyl complexes indicate the formation of either a monomeric or a possible dimeric complex with each phenolic O atom bridging between two metal centers. Labeling with [ (99m)Tc(CO) 3] (+) provided further insight into the differences in complex formation on the dilute, no carrier added, level compared to the macroscopic scale at which the Re (I) counterparts were made. These new tridentate, monoanionic ligands are competent chelates in binding the [ (99m)Tc(CO) 3] (+) core because radiolabeling yields ranged from 85 to 99% and the resulting complexes were stable to cysteine and histidine challenges for as long as 24 h.

Synthesis, characterization, and metal coordinating ability of multifunctional carbohydrate-containing compounds for Alzheimer's therapy.

Dysfunctional interactions of metal ions, especially Cu, Zn, and Fe, with the amyloid-beta (A beta) peptide are hypothesized to play an important role in the etiology of Alzheimer's disease (AD). In addition to direct effects on A beta aggregation, both Cu and Fe catalyze the generation of reactive oxygen species (ROS) in the brain further contributing to neurodegeneration. Disruption of these aberrant metal-peptide interactions via chelation therapy holds considerable promise as a therapeutic strategy to combat this presently incurable disease. To this end, we developed two multifunctional carbohydrate-containing compounds N,N'-bis[(5-beta-D-glucopyranosyloxy-2-hydroxy)benzyl]-N,N'-dimethyl-ethane-1,2-diamine (H2GL1) and N,N'-bis[(5-beta-D-glucopyranosyloxy-3-tert-butyl-2-hydroxy)benzyl]-N,N'-dimethyl-ethane-1,2-diamine (H2GL2) for brain-directed metal chelation and redistribution. Acidity constants were determined by potentiometry aided by UV-vis and 1H NMR measurements to identify the protonation sites of H2GL1,2. Intramolecular H bonding between the amine nitrogen atoms and the H atoms of the hydroxyl groups was determined to have an important stabilizing effect in solution for the H2GL1 and H2GL2 species. Both H2GL1 and H2GL2 were found to have significant antioxidant capacity on the basis of an in vitro antioxidant assay. The neutral metal complexes CuGL1, NiGL1, CuGL2, and NiGL2 were synthesized and fully characterized. A square-planar arrangement of the tetradentate ligand around CuGL2 and NiGL2 was determined by X-ray crystallography with the sugar moieties remaining pendant. The coordination properties of H2GL1,2 were also investigated by potentiometry, and as expected, both ligands displayed a higher affinity for Cu2+ over Zn2+ with H2GL1 displaying better coordinating ability at physiological pH. Both H2GL1 and H2GL2 were found to reduce Zn2+- and Cu2+- induced Abeta1-40 aggregation in vitro, further demonstrating the potential of these multifunctional agents as AD therapeutics.