Rivastigmine-Benzimidazole Hybrids as Promising Multitarget Metal-Modulating Compounds for Potential Treatment of Neurodegenerative Diseases.

With the goal of combating the multi-faceted Alzheimer's disease (AD), a series of Rivastigmine-Benzimidazole (RIV-BIM) hybrids was recently reported by us as multitarget-directed ligands, thanks to their capacity to tackle important hallmarks of AD. In particular, they exhibited antioxidant activity, acted as cholinesterase inhibitors, and inhibited amyloid-ß (Aß) aggregation. Herein, we moved forward in this project, studying their ability to chelate redox-active biometal ions, Cu(II) and Fe(III), with widely recognized roles in the generation of oxidative reactive species and in protein misfolding and aggregation in both AD and Parkinson's disease (PD). Although Cu(II) chelation showed higher efficiency for the positional isomers of series 5 than those of series 4 of the hybrids, the Aß-aggregation inhibition appears more dependent on their capacity for fibril intercalation than on copper chelation. Since monoamine oxidases (MAOs) are also important targets for the treatment of AD and PD, the capacity of these hybrids to inhibit MAO-A and MAO-B was evaluated, and they showed higher activity and selectivity for MAO-A. The rationalization of the experimental evaluations (metal chelation and MAO inhibition) was supported by computational molecular modeling studies. Finally, some compounds showed also neuroprotective effects in human neuroblastoma (SH-SY5Y cells) upon treatment with 1-methyl-4-phenylpyridinium (MPP+), a neurotoxic metabolite of a Parkinsonian-inducing agent.

Hydroxypyridinone-Based Metal Chelators towards Ecotoxicity: Remediation and Biological Mechanisms.

Hydroxypyridinones (HPs) are recognized as excellent chemical tools for engineering a diversity of metal chelating agents, with high affinity for hard metal ions, exhibiting a broad range of activities and applications, namely in medical, biological and environmental contexts. They are easily made and functionalizable towards the tuning of their pharmacokinetic properties or the improving of their metal complex thermodynamic stabilities. In this review, an analysis of the recently published works on hydroxypyridinone-based ligands, that have been mostly addressed for environmental applications, namely for remediation of hard metal ion ecotoxicity in living beings and other biological matrices is carried out. In particular, herein the most recent developments in the design of new chelating systems, from bidentate mono-HP to polydentate multi-HP derivatives, with a structural diversity of soluble or solid-supported backbones are outlined. Along with the ligand design, an analysis of the relationship between their structures and activities is presented and discussed, namely associated with the metal affinity and the thermodynamic stability of the corresponding metal complexes.

A Multi-Technique Investigation of the Complex Formation Equilibria between Bis-Deferiprone Derivatives and Oxidovanadium (IV).

The increasing biomedical interest in high-stability oxidovanadium(IV) complexes with hydroxypyridinone ligands leads us to investigate the complex formation equilibria of VIVO2+ ion with a tetradentate ligand, named KC21, which contains two 3-hydroxy-1,2-dimethylpyridin-4(1H)-one (deferiprone) moieties, and with the simple bidentate ligand that constitutes the basic unit of KC21, for comparison, named L5. These equilibrium studies were conducted with joined potentiometric-spectrophotometric titrations, and the results were substantiated with EPR measurements at variable pH values. This multi-technique study gave evidence of the formation of an extremely stable 1:1 complex between KC21 and oxidovanadium(IV) at a physiological pH, which could find promising pharmacological applications.

Multifunctional Small Molecules as Potential Anti-Alzheimer's Disease Agents.

Alzheimer's disease (AD) is a severe multifactorial neurodegenerative disorder characterized by a progressive loss of neurons in the brain. Despite research efforts, the pathogenesis and mechanism of AD progression are not yet completely understood. There are only a few symptomatic drugs approved for the treatment of AD. The multifactorial character of AD suggests that it is important to develop molecules able to target the numerous pathological mechanisms associated with the disease. Thus, in the context of the worldwide recognized interest of multifunctional ligand therapy, we report herein the synthesis, characterization, physicochemical and biological evaluation of a set of five (1a-e) new ferulic acid-based hybrid compounds, namely feroyl-benzyloxyamidic derivatives enclosing different substituent groups, as potential anti-Alzheimer's disease agents. These hybrids can keep both the radical scavenging activity and metal chelation capacity of the naturally occurring ferulic acid scaffold, presenting also good/mild capacity for inhibition of self-Aß aggregation and fairly good inhibition of Cu-induced Aß aggregation. The predicted pharmacokinetic properties point towards good absorption, comparable to known oral drugs.

Novel Donepezil-Arylsulfonamide Hybrids as Multitarget-Directed Ligands for Potential Treatment of Alzheimer's Disease.

Alzheimer's disease (AD) is one of the most devastating neurodegenerative disorders, characterized by multiple pathological features. Therefore, multi-target drug discovery has been one of the most active fields searching for new effective anti-AD therapies. Herein, a series of hybrid compounds are reported which were designed and developed by combining an aryl-sulfonamide function with a benzyl-piperidine moiety, the pharmacophore of donepezil (a current anti-AD acetylcholinesterase AChE inhibitor drug) or its benzyl-piperazine analogue. The in vitro results indicate that some of these hybrids achieve optimized activity towards two main AD targets, by displaying excellent AChE inhibitory potencies, as well as the capability to prevent amyloid-ß (Aß) aggregation. Some of these hybrids also prevented Aß-induced cell toxicity. Significantly, drug-like properties were predicted, including for blood-brain permeability. Compound 9 emerged as a promising multi-target lead compound (AChE inhibition (IC50 1.6 µM); Aß aggregation inhibition 60.7%). Overall, this family of hybrids is worthy of further exploration, due to the wide biological activity of sulfonamides.

Novel tacrine-benzofuran hybrids as potential multi-target drug candidates for the treatment of Alzheimer's Disease.

Pursuing the widespread interest on multi-target drugs to combat Alzheimer´s disease (AD), a new series of hybrids was designed and developed based on the repositioning of the well-known acetylcholinesterase (AChE) inhibitor, tacrine (TAC), by its coupling to benzofuran (BF) derivatives. The BF framework aims to endow the conjugate molecules with ability for inhibition of AChE (bimodal way) and of amyloid-beta peptide aggregation, besides providing metal (Fe, Cu) chelating ability and concomitant extra anti-oxidant activity, for the hybrids with hydroxyl substitution. The new TAC-BF conjugates showed very good activity for AChE inhibition (sub-micromolar range) and good capacity for the inhibition of self- and Cu-mediated Aß aggregation, with dependence on the linker size and substituent groups of each main moiety. Neuroprotective effects were also found for the compounds through viability assays of neuroblastoma cells, after Aß1-42 induced toxicity. Structure-activity relationship analysis provides insights on the best structural parameters, to take in consideration for future studies in view of potential applications in AD therapy.

Deep Eutectic Solvents as Effective Reaction Media for the Synthesis of 2-Hydroxyphenylbenzimidazole-based Scaffolds en Route to Donepezil-Like Compounds.

An unsubstituted 2-hydroxyphenylbenzimidazole has recently been included as a scaffold in a series of hybrids (including the hit compound PZ1) based on the framework of the acetylcholinesterase (AChE) inhibitor Donepezil, which is a new promising multi-target ligand in Alzheimer's disease (AD) treatment. Building upon these findings, we have now designed and completed the whole synthesis of PZ1 in the so-called deep eutectic solvents (DESs), which have emerged as an unconventional class of bio-renewable reaction media in green synthesis. Under optimized reaction conditions, the preparation of a series of 2-hydroxyphenylbenzimidazole-based nuclei has also been perfected in DESs, and comparison with other routes which employ toxic and volatile organic solvents (VOCs) provided. The functionalization of the aromatic ring can have implications on some important biological properties of the described derivatives and will be the subject of future studies of structure-activity relationships (SARs).

Design, Synthesis, and In Vitro Evaluation of Hydroxybenzimidazole-Donepezil Analogues as Multitarget-Directed Ligands for the Treatment of Alzheimer's Disease.

A series of multi-target-directed ligands (MTDLs), obtained by attachment of a hydroxyphenylbenzimidazole (BIM) unit to donepezil (DNP) active mimetic moiety (benzyl-piperidine/-piperazine) was designed, synthesized, and evaluated as potential anti-Alzheimer's disease (AD) drugs in terms of biological activity (inhibition of acetylcholinesterase (AChE) and ß-amyloid (Aß) aggregation), metal chelation, and neuroprotection capacity. Among the DNP-BIM hybrids studied herein, the structural isomerization did not significantly improve the biological properties, while some substitutions, namely fluorine atom in each moiety or the methoxy group in the benzyl ring, evidenced higher cholinergic AChE activity. All the compounds are able to chelate Cu and Zn metal ions through their bidentate BIM moieties, but compound 5, containing a three-dentate chelating unit, is the strongest Cu(II) chelator. Concerning the viability on neuroblastoma cells, compounds 9 and 10 displayed the highest reduction of Aß-induced cell toxicity. In silico calculations of some pharmacokinetic descriptors indicate that all the compounds but the nitro derivatives have good potential oral-bioavailability. Overall, it can be concluded that most of the studied DNP-BIM conjugates showed quite good anti-AD properties, therefore deserving to be considered in further studies with the aim of understanding and treating AD.

New Multitarget Hybrids Bearing Tacrine and Phenylbenzothiazole Motifs as Potential Drug Candidates for Alzheimer's Disease.

Research on neurodegenerative brain disorders, namely the age-dependent Alzheimer's disease (AD), has been intensified in the last decade due to the absence of a cure and the recognized increasing of life expectancy for populations. To address the multifactorial nature and complexity of AD, a multi-target-directed ligand approach was herein employed, by designing a set of six selected hybrids (14⁻19) that combine in the same entity two pharmacophores: tacrine (TAC) and 2-phenylbenzothiazole (PhBTA). The compounds contain a methoxy substituent at the PhBTA moiety and have a variable length linker between that and the TAC moiety. The docking studies showed that all the compounds assure a dual-binding mode of acetylcholinesterase (AChE) inhibition, establishing π-stacking and H-bond interactions with aminoacid residues at both active binding sites of the enzyme (CAS and PAS). The bioassays revealed that the designed compounds display excellent AChE inhibitory activity in the sub-micromolar range (0.06⁻0.27 µM) and moderate inhibition values for amyloid-ß (Aß) self-aggregation (27⁻44.6%), compounds 14 and 15 being the lead compounds. Regarding neuroprotective effects in neuroblastoma cells, compounds 15, 16 and 19 revealed the capacity to prevent Aß-induced toxicity, but compound 16 showed the highest neuroprotective effect. Overall these hybrid compounds, in particular 15 and 16, with promising multitarget anti-AD ability, encourage further pursuing studies on this type of TAC-PhBTA derivatives for potential AD therapy.

Donepezil structure-based hybrids as potential multifunctional anti-Alzheimer's drug candidates.

A new series of multifunctional hybrids, based on the structure of the donepezil (DNP) drug, have been developed and evaluated as potential anti Alzheimer's disease (AD) agents. The rationale of this study was the conjugation of a benzylpiperidine/benzylpiperazine moiety with derivatives of bioactive heterocyclics (benzimidazole or benzofuran), to mimic the main structure of DNP and to endow the hybrids with additional relevant properties such as inhibition of amyloid beta (Aß) peptide aggregation, antioxidant activity and metal chelation. Overall, they showed good activity for AChE inhibition (IC50=4.0-30.0 µΜ) and moderate ability for inhibition of Aß1-42 self-mediated aggregation. The hybrids containing chelating groups showed improvement in the inhibition of Cu-induced Aß42 aggregation and the antioxidant capacity. Moreover, neuroprotective effects of these compounds were evidenced in neuroblastoma cells after Aß1-42 induced toxicity. Structure-activity relationship allowed the identification of some promising compounds and the main determinant structural features for the targeted properties.

New Multitarget Rivastigmine-Indole Hybrids as Potential Drug Candidates for Alzheimer's Disease.

Alzheimer's disease (AD) is the most common form of dementia with no cure so far, probably due to the complexity of this multifactorial disease with diverse processes associated with its origin and progress. Several neuropathological hallmarks have been identified that encourage the search for new multitarget drugs. Therefore, following a multitarget approach, nine rivastigmine-indole (RIV-IND) hybrids (5a1-3, 5b1-3, 5c1-3) were designed, synthesized and evaluated for their multiple biological properties and free radical scavenging activity, as potential multitarget anti-AD drugs. The molecular docking studies of these hybrids on the active center of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) suggest their capacity to act as dual enzyme inhibitors with probable greater disease-modifying impact relative to AChE-selective FDA-approved drugs. Compounds 5a3 (IC50 = 10.9 µM) and 5c3 (IC50 = 26.8 µM) revealed higher AChE inhibition than the parent RIV drug. Radical scavenging assays demonstrated that all the hybrids containing a hydroxyl substituent in the IND moiety (5a2-3, 5b2-3, 5c2-3) have good antioxidant activity (EC50 7.8-20.7 µM). The most effective inhibitors of Aß42 self-aggregation are 5a3, 5b3 and 5c3 (47.8-55.5%), and compounds 5b2 and 5c2 can prevent the toxicity induced by Aß1-42 to cells. The in silico evaluation of the drug-likeness of the hybrids also showed that all the compounds seem to have potential oral availability. Overall, within this class of RIV-IND hybrids, 5a3 and 5c3 appear as lead compounds for anti-AD drug candidates, deserving further investigation.

Design, synthesis and neuroprotective evaluation of novel tacrine-benzothiazole hybrids as multi-targeted compounds against Alzheimer's disease.

Alzheimer's disease (AD) is a multifactorial disorder with several target proteins contributing to its etiology. In search for multifunctional anti-AD drug candidates, taking into account that the acetylcholinesterase (AChE) and beta-amyloid (Aß) aggregation are particularly important targets for inhibition, the tacrine and benzothiazole (BTA) moieties were conjugated with suitable linkers in a novel series of hybrids. The designed compounds (7a-7e) were synthesized and in vitro as well as in ex vivo evaluated for their capacity for the inhibition of acetylcholinesterase (AChE) and Aß self-induced aggregation, and also for the protection of neuronal cells death (SHSY-5Y cells, AD and MCI cybrids). All the tacrine-BTA hybrids displayed high in vitro activities, namely with IC50 values in the low micromolar to sub-micromolar concentration range towards the inhibition of AChE, and high percentages of inhibition of the self-induced Aß aggregation. Among them, compound 7a, with the shortest linker, presented the best inhibitory activity of AChE (IC50=0.34 µM), while the highest activity as anti-Aß42 self-aggregation, was evidenced for compound 7b (61.3%, at 50µM. The docking studies demonstrated that all compounds are able to interact with both catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Our results show that compounds 7d and 7e improved cell viability in cells treated with Aß42 peptide. Overall, these multi-targeted hybrid compounds appear as promising lead compounds for the treatment of Alzheimer's disease.

A novel organic semiconductor 4-phenylthiazol-2-yl-(phenylhydrazono) acetonitrile (PTPA) thin films: synthesis, optical and electrical properties.

In this study, 4-phenylthiazol-2-yl-(phenylhydrazono) acetonitrile (PTPA) azo dye was synthesized and studied from optical and electrical point of view. The tautomerization phenomenon of the PTPA dye was clarified using one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (1HNMR and 13C NMR), absorbance (UV-Vis), emission, and Fourier transform infrared spectroscopy (FT-IR). X-ray diffraction (XRD) evaluations were indicated that PTPA in powder and thin films crystallizes in a monoclinic system structure with nonstructural characteristics. Spectrophotometric measurements of absorbance A (λ), transmittance T (λ) and reflectance R (λ) at normal incidence light in the wavelength range 200-2500 nm were used to determine the optical band gap, extinction coefficient, k and refractive index, n. Also, non-linear optical parameters such as the third order non-linear susceptibility, χ(3) and nonlinear refractive index, n(2) of PTPA have revealed an awe-inspiring switching behavior, implying the possibility of using PTPA in optical switching systems. Finally, the electrical conductivity of the PTPA was shown to increase with rising temperature, indicating that it is a typical organic semiconductor. Mott's parameters were determined and discussed at low temperatures. Thus, PTPA is a promising organic semiconductor with broad utility potential in organic electronics such as organic light-emitting diodes (OLEDs).

GdIII and GaIII complexes with a new tris-3,4-HOPO ligand as new imaging probes: complex stability, magnetic properties and biodistribution.

The development of metal-based multimodal imaging probes is a highly challenging field in coordination chemistry. In this context, we have developed a bifunctional hexadentate tripodal ligand (H3L2) with three 3,4-HOPO moieties attached to a flexible tetrahedral carbon bearing a functionalizable nitro group. Complexes formed with different metal ions have potential interest for diagnostic applications, namely magnetic resonance imaging (MRI) and positron emission tomography (PET). The capacity of the ligand to coordinate GdIII and GaIII was studied and the thermodynamic stability constants of the respective complexes were determined by potentiometry and spectrophotometry. The ligand forms stable 1 : 1 ML complexes though with considerably higher affinity for GaIII than for GdIII (pGa = 26.2 and pGd = 14.3 at pH 7). The molecular dynamics simulations of the GdIII complex indicate that two water molecules can coordinate the metal ion, thus providing efficient paramagnetic enhancement of water proton relaxation. The relaxation and the water exchange properties of the GdIII chelate, assessed by a combined 17O NMR and 1H NMRD study, showed associative activated water exchange with a relatively low rate constant, k298ex = (0.82 ± 0.11) × 107 s-1, and some aggregation tendency. Biodistribution studies of the 67Ga-L2 complex suggested good in vivo stability and quick renal clearance. Further anchoring of this ligand with specific biotargeting moieties might open future prospectives for applications of labelled conjugates in both MRI and 68Ga-PET diagnostic imaging.

Novel Rivastigmine Derivatives as Promising Multi-Target Compounds for Potential Treatment of Alzheimer's Disease.

Alzheimer's disease (AD) is the most serious and prevalent neurodegenerative disorder still without cure. Since its aetiology is diverse, recent research on anti-AD drugs has been focused on multi-target compounds. In this work, seven novel hybrids (RIV-BIM) conjugating the active moiety of the drug rivastigmine (RIV) with 2 isomeric hydroxyphenylbenzimidazole (BIM) units were developed and studied. While RIV assures the inhibition of cholinesterases, BIM provides further appropriate properties, such as inhibition of amyloid ß-peptide (Aß) aggregation, antioxidation and metal chelation. The evaluated biological properties of these hybrids included antioxidant activity; inhibition of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and Aß42 aggregation; as well as promotion of cell viability and neuroprotection. All the compounds are better inhibitors of AChE than rivastigmine (IC50 = 32.1 µM), but compounds of series 5 are better inhibitors of BChE (IC50 = 0.9-1.7 µM) than those of series 4. Series 5 also showed good capacity to inhibit self- (42.1-58.7%) and Cu(II)-induced (40.3-60.8%) Aß aggregation and also to narrow (22.4-42.6%) amyloid fibrils, the relevant compounds being 5b and 5d. Some of these compounds can also prevent the toxicity induced in SH-SY5Y cells by Aß42 and oxidative stress. Therefore, RIV-BIM hybrids seem to be potential drug candidates for AD with multi-target abilities.

Structure-based design of novel donepezil-like hybrids for a multi-target approach to the therapy of Alzheimer's disease.

Alzheimer's disease (AD) is a widespread multifactorial aging-related pathology, which includes cholinergic deficit among its main causes. Following a multi-target design strategy, the structure of the approved drug donepezil was taken as the starting point for generating some new potential multi-functional compounds. Therefore, a series of twenty molecular hybrids were synthesized and assayed against three different enzymes, namely the well-established targets acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and the innovative one fatty acid amide hydrolase (FAAH). In silico studies confirmed the interaction of benzylpiperidine and the benzylpiperazine isostere with the catalytic anionic site (CAS) of AChE, while the aryloxycarbonyl portion appeared to be important for the interaction with the peripheral site (PAS). A QSAR study was carried out on AChE inhibition data, which revealed that the inhibition potency seems to depend upon the length of the spacer and the number of polar atoms. The docking poses of selected compounds within BChE and FAAH were also calculated. Furthermore, pharmacokinetics and drug-likeness properties were assessed by chemoinformatic tools. Several piperidine derivatives (in particular compound 10) showed interesting profiles as multi-target directed agents, while the lead piperazine derivative 12 (SON38) was found to be a more potent and selective AChE inhibitor (IC50 = 0.8 nM) than donepezil, besides being able to bind bivalent copper cations (pCu = 7.9 at physiological pH). Finally, the selected lead compounds (10 and 12, SON38) did not show significant cytotoxicity on SH-SY5Y and HepG2 cells at the highest tested concentration (100 µM) in a MTT assay.

Bifunctional phenolic-choline conjugates as anti-oxidants and acetylcholinesterase inhibitors.

Because of the complex cascade of molecular events that can occur in the brain of an Alzheimer's disease (AD) patient, the therapy of this neurodegenerative disease seems more likely to be achieved by multifunctional drugs. Herein, a new series of dual-targeting ligands have been developed and in vitro bioevaluated. Their architecture is based on conjugating the acetylcholinesterase inhibition and anti-oxidant properties in one molecular entity. Specifically, a series of naturally occurring phenolic acids with recognized anti-oxidant properties (derivatives of caffeic acid, rosmarinic acid, and trolox) have been conjugated with choline to account for the recognition by acetylcholinesterase (AChE). The synthesized hybrid compounds evidenced AChE inhibitory capacity of micromolar range (rationalized by molecular modeling studies) and good antioxidant properties. Their effects on human neuroblastoma cells, previously treated with beta-amyloid peptides and 1-methyl-4-phenylpyridinium ion neurotoxins (to simulate AD and Parkinson's disease, respectively), also demonstrated a considerable capacity for protection against the cytotoxicity of these stressors.

Recent Multi-target Approaches on the Development of Anti- Alzheimer's Agents Integrating Metal Chelation Activity.

Alzheimer´s disease (AD) is the most common and severe age-dependent neurodegenerative disorder worldwide. Notwithstanding the large amount of research dedicated to both the elucidation of this pathology and the development of an effective drug, the multifaceted nature and complexity of the disease are certainly a rationale for the absence of cure so far. Currently available drugs are used, mainly to compensate the decline of the neurotransmitter acetylcholine by acetylcholinesterase (AChE) inhibition, though they only provide temporary symptomatic benefits and cannot stop AD progression. Although the multiple factors that contribute to trigger AD onset and progression are not yet fully understood, several pathological features and underneath pathways have been recognized to contribute to its pathology, such as metal dyshomeostasis, protein misfolding, oxidative stress and neurotransmitter deficiencies, some of them being interconnected. Thus, there is widespread recent interest in the development of multitarget-directed ligands (MTDLs) for simultaneous interaction with several pathological targets of AD. In this review, a selection of the most recent reports (2016-up to present) on metal chelators of MTDLs with multifunctionalities is presented. These compounds enable the hitting of several AD targets or pathways, such as modulation of specific biometal ions (e.g., Cu, Fe, Zn) and of protein misfolding (ß-amyloid and tau protein), anti-oxidant activity and AChE inhibition. The properties found for these hybrids are discussed in comparison with the original reference compounds, some MTDLs being outlined as leading compounds for pursuing future studies in view of efficient potential applications in AD therapy.

Derivatives of Tenuazonic Acid as Potential New Multi-Target Anti-Alzheimer's Disease Agents.

Alzheimer's disease (AD) is generally recognized as a multifactorial neurodegenerative pathology with an increasing impact on society. Tenuazonic acid (TA) is a natural compound that was recently identified as a potential multitarget ligand with anti-cholinesterase, anti-amyloidogenic and antioxidant activities. Using its structure as a chemical scaffold, we synthesized and evaluated new derivatives (1-5), including tenuazonic-donepezil (TA-DNP) hybrids (4 and 5) due to the clinical importance of the anti-AD drug donepezil. These novel compounds all achieved activity in the micromolar range towards all selected targets and demonstrated to be potentially orally absorbed. Moreover, a selected compound (1) was further investigated as a chelating agent towards copper (II), zinc (II) and iron (III) and showed good chelating ability (pFe = 16.6, pCu = 11.6, pZn = 6.0 at pH 7.4). Therefore, the TA motif can be considered an interesting building block in the search for innovative multi-functional anti-neurodegenerative drugs, as exemplified by hybrid 5, a promising non-cytotoxic lead compound adequate for the early stages of AD, and capable of ameliorating the oxidative status of SH-SY5Y human neuroblastoma cells.

New tris(hydroxypyridinones) as iron and aluminium sequestering agents: synthesis, complexation and in vivo studies.

Two new tripodal tris(3-hydroxy-4-pyridinone) hexadentate chelators-NTA(BuHP)(3) and NTP(PrHP)(3) (NTA=nitrilotriacetic acid, NTP=nitrilotripropionic acid, HP=hydroxypyridone)-have been developed and studied in solution for their iron and aluminium binding affinity, and also assayed in vivo for their capacity to remove metal from an animal model that is overloaded. These chelators are positional isomers, possessing identical general structures based on aminotricarboxylic acid skeletons attached to three bidentate 3-hydroxy-4-pyridinones (3,4-HPs), but differing in the position of the amide linkage along the chelating "arm". In spite of expected differences in the tripodal ligands, such as acidity and hydrogen-bonding networks, they share important properties, namely, a mild hydrophilic character (log P ca. -1.2 to -1.4) and a strong chelating affinity for Fe and Al (pFe=27.9 and pAl=22.0 for NTA(BuHP)(3); pFe=29.4 and pAl=22.4 for NTP(PrHP)(3)). They also evidenced identical effects on the biodistribution and on the excretion of a radiotracer ((67)Ga) previously administered to mice, as models of iron overload animals. Comparison of the new compounds with reported analogues shows good improvement in terms of solution and in vivo sequestering properties, thus giving support to expectations about their potential clinical application as metal removal agents.