Importance of the Dimethylamino Functionality on a Multifunctional Framework for Regulating Metals, Amyloid-β, and Oxidative Stress in Alzheimer's Disease

Room-Temperature Dialkylamination of Chloroheteroarenes Using a Cu(II)/PTABS Catalytic System

The dimethylamino functionality has significant importance in industrially relevant molecules and methodologies to install these efficiently are highly desirable. We report herein a highly efficient, room-temperature dimethylamination of chloroheteroarenes performed via the in-situ generation of dimethylamine using N,N-dimethylformamide (DMF) as precursor wiith a large substrate scope that includes various heteroarenes, purines as well as commercially relevant drugs such as altretamine, ampyzine and puromycin precursor.

Identification of Multi-Target Anti-AD Chemical Constituents From Traditional Chinese Medicine Formulae by Integrating Virtual Screening and In Vitro Validation

Alzheimer's disease (AD) is a neurodegenerative disease that seriously threatens the health of the elderly. At present, no drugs have been proven to cure or delay the progression of the disease. Due to the multifactorial aetiology of this disease, the multi-target-directed ligand (MTDL) approach provides an innovative and promising idea in search for new drugs against AD. In order to find potential multi-target anti-AD drugs from traditional Chinese medicine (TCM) formulae, a compound database derived from anti-AD Chinese herbal formulae was constructed and predicted by the anti-AD multi-target drug prediction platform established in our laboratory. By analyzing the results of virtual screening, 226 chemical constituents with 3 or more potential AD-related targets were collected, from which 16 compounds that were predicted to combat AD through various mechanisms were chosen for biological validation. Several cell models were established to validate the anti-AD effects of these compounds, including KCl, Aβ, okadaic acid (OA), SNP and H₂O₂ induced SH-SY5Y cell model and LPS induced BV2 microglia model. The experimental results showed that 12 compounds including Nonivamide, Bavachromene and 3,4-Dimethoxycinnamic acid could protect model cells from AD-related damages and showed potential anti-AD activity. Furthermore, the potential targets of Nonivamide were investigated by molecular docking study and analysis with CDOCKER revealed the possible binding mode of Nonivamide with its predicted targets. In summary, 12 potential multi-target anti-AD compounds have been found from anti-AD TCM formulae by comprehensive application of computational prediction, molecular docking method and biological validation, which laid a theoretical and experimental foundation for in-depth study, also providing important information and new research ideas for the discovery of anti-AD compounds from traditional Chinese medicine.

Synthesis, characterization, and supramolecular architectures of two distinct classes of probes for the visualization of endogenously generated hypochlorite ions in response to cellular activity

Two distinct classes of compounds, (E)-2-(((3-amino-4-nitrophenyl) imino) methyl)-5-(diethylamino) phenol (SB) and 5-(diethylamino)-2-(5-nitro-1H-benzo[d]imidazol-2-yl) phenol (IM) were synthesized. SB, a bright red colored compound was crystallized in acetonitrile as a triclinic crystal system while IM, yellow colored compound crystallized as a monoclinic crystal system in dimethylformamide by vapor diffusion of diethylether. These compounds were characterized using spectroscopic techniques (IR, UV-visible, ¹H, and ¹³C NMR), and X-ray crystallography. SB and IM displayed classical and non-classical H-bonding involving C-H…O and π…π interactions. These compounds detected hypochlorite ions in aqueous DMSO (1: 9, v/v, HEPES buffer, pH 7.4), and detection was visible via color changes by naked eye. We also performed UV-visible and fluorescence titrations, showing detection limits of 8.82 × 10^-7 M for SB and 2.44 × 10^-7 M for IM. The fluorometric responses from SB and IM were also studied against different ROS and anions. DFT calculations were performed to strengthen the proposed sensing mechanisms of both SB and IM. Hypochlorite, which is endogenously generated by myeloperoxidase in endosomes, was specifically visualized using SB and IM in lipopolysaccharide-treated RAW264.7 cells. These probes were also used to image the generation of hypochlorite by RAW264.7 cells during phagocytosis of non-fluorescent polystyrene beads.

Advances in Multi-Functional Ligands and the Need for Metal-Related Pharmacology for the Management of Alzheimer Disease

Alzheimer’s disease (AD) is the age linked neurodegenerative disorder with no disease modifying therapy currently available. The available therapy only offers short term symptomatic relief. Several hypotheses have been suggested for the pathogenesis of the disease while the molecules developed as possible therapeutic agent in the last decade, largely failed in the clinical trials. Several factors like tau protein hyperphosphorylation, amyloid-β (Aβ) peptide aggregation, decline in acetyl cholinesterase and oxidative stress might be contributing toward the pathogenesis of AD. Additionally, biometals dyshomeostasis (Iron, Copper, and Zinc) in the brain are also reported to be involved in the pathogenesis of AD. Thus, targeting these metal ions may be an effective strategy for the development of a drug to treat AD. Chelation therapy is currently employed for the metal intoxication but we lack a safe and effective chelating agents with additional biological properties for their possible use as multi target directed ligands for a complex disease like AD. Chelating agents possess the ability to disaggregate Aβ aggregation, dissolve amyloid plaques, and delay the cognitive impairment. Thus there is an urgent need to develop disease modifying therapeutic molecules with multiple beneficial features like targeting more than one factor responsible of the disease. These molecules, as disease modifying therapeutic agents for AD, should possess the potential to inhibit Aβ-metal interactions, the formation of toxic Aβ aggregates; and the capacity to reinstate metal homeostasis.

Tailoring Hydrophobic Interactions between Probes and Amyloid-β Peptides for Fluorescent Monitoring of Amyloid-β Aggregation

Despite their unique advantages, the full potential of molecular probes for fluorescent monitoring of amyloid-β (Aβ) aggregates has not been fully exploited. This limited utility stems from the lack of knowledge about the hydrophobic interactions between the molecules of Aβ probes, as well as those between the probe and the Aβ aggregate. Herein, we report the first mechanistic study, which firmly establishes a structure-signaling relationship of fluorescent Aβ probes. We synthesized a series of five fluorescent Aβ probes based on an archetypal donor-acceptor-donor scaffold (denoted as SN1-SN5). The arylamino donor moieties were systematically varied to identify molecular factors that could influence the interactions between molecules of each probe and that could influence their fluorescence outcomes in conditions mimicking the biological milieu. Our probes displayed different responses to aggregates of Aβ, Aβ40 and Aβ42, two major isoforms found in Alzheimer's disease: SN2, having pyrrolidine donors, showed noticeable ratiometric fluorescence responses (Δν = 797 cm-1) to the Aβ40 and Aβ42 samples that contained oligomeric species, whereas SN4, having N-methylpiperazine donors, produced significant fluorescence turn-on signaling in response to Aβ aggregates, including oligomers, protofibrils, and fibrils (with turn-on ratios of 14 and 10 for Aβ42 and Aβ40, respectively). Mechanistic investigations were carried out by performing field-emission scanning electron microscopy, X-ray crystallography, UV-vis absorption spectroscopy, and steady-state and transient photoluminescence spectroscopy experiments. The studies revealed that the SN probes underwent preassembly prior to interacting with the Aβ species and that the preassembled structures depended profoundly on the subtle differences between the amino moieties of the different probes. Importantly, the studies demonstrated that the mode of fluorescence signaling (i.e., ratiometric response versus turn-on response) was primarily governed by stacking geometries within the probe preassemblies. Specifically, ratiometric fluorescence responses were observed for probes capable of forming J-assembly, whereas fluorescence turn-on responses were obtained for probes incapable of forming J-aggregates. This finding provides an important guideline to follow in future efforts at developing fluorescent probes for Aβ aggregation. We also conclude, on the basis of our study, that the rational design of such fluorescent probes should consider interactions between the probe molecules, as well as those between Aβ peptides and the probe molecule.

A small bifunctional chelator that modulates Aβ42 aggregation

Multifunctional compounds that can modulate amyloid-β (Aβ) aggregation and interact with metal ions hold considerable promise as therapeutic agents for Alzheimer’s disease (AD). Using the copper-catalyzed azide-alkyne cycloaddition reaction, a novel bifunctional chelator 2-(1-(4-(dimethylamino)benzyl)-1H-1,2,3-triazol-4-yl)phenol (L1) was synthesized. L1 contains a bidentate metal-binding unit and a pendant dimethylamino moiety. The product was characterized by 1H NMR, 13C NMR, and MS. The metal-binding properties of L1 were probed by UV–vis spectroscopy to determine Cu:L stoichiometry. L1 was determined to limit Aβ aggregation at 48 h via a ThT assay. In addition, L1 complies with Lipinski’s rules and calculated logBB values for potential drug likeness and BBB permeability. These results suggest that L1 is a suitable candidate for further study as a multifunctional compound to treat AD.

Dynamic micellar oligomers of amyloid beta peptides play a crucial role in their aggregation mechanisms

Aβ40 and Aβ42 peptides form micellar precursors of amyloid nuclei contributing to important differences in their aggregation pathways.

Synthesis, Characterization, and Activity of a Triazine Bridged Antioxidant Small Molecule

Metal-ion misregulation and oxidative stress continue to be components of the continually evolving hypothesis describing the molecular origins of Alzheimer's disease. Therefore, these features are viable targets for synthetic chemists to explore through hybridizations of metal-binding ligands and antioxidant units. To date, the metal-binding unit in potential therapeutic small molecules has largely been inspired by clioquinol with the exception of a handful of heterocyclic small molecules and open-chain systems. Heterocyclic small molecules such as cyclen (1,4,7,10-tetraazacyclododecane) have the advantage of straightforward N-based modifications, allowing the addition of functional groups. In this work, we report the synthesis of a triazine bridged system containing two cyclen metal-binding units and an antioxidant coumarin appendage inspired by nature. This new potential therapeutic molecule shows the ability to bind copper in a unique manner compared to other chelates proposed to treat Alzheimer's disease. DPPH and TEAC assays exploring the activity of N-(2-((4,6-di(1,4,7,10-tetraazacyclododecan-1-yl)-1,3,5-triazin-2-yl)amino)ethyl)-2-oxo-2H-chromene-3-carboxamide (molecule 1) show that the molecule is antioxidant. Cellular studies of molecule 1 indicate a low toxicity (EC₅₀ = 80 μM) and the ability to protect HT-22 neuronal cells from cell death induced by Aβ + copper(II), thus demonstrating the potential for molecule 1 to serve as a multimodal therapeutic for Alzheimer's disease.

Structural and Mechanistic Insights into Development of Chemical Tools to Control Individual and Inter-Related Pathological Features in Alzheimer's Disease

To elucidate the involvement of individual and inter-related pathological factors [i.e., amyloid-β (Aβ), metals, and oxidative stress] in the pathogenesis of Alzheimer's disease (AD), chemical tools have been developed. Characteristics required for such tool construction, however, have not been clearly identified; thus, the optimization of available tools or new design has been limited. Here, key structural properties and mechanisms that can determine tools' regulatory reactivities with multiple pathogenic features found in AD are reported. A series of small molecules was built up through rational structural selection and variations onto the framework of a tool useful for in vitro and in vivo metal-Aβ investigation. Variations include: (i) location and number of an Aβ interacting moiety; (ii) metal binding site; and (iii) denticity and structural flexibility. Detailed biochemical, biophysical, and computational studies were able to provide a foundation of how to originate molecular formulas to devise chemical tools capable of controlling the reactivities of various pathological components through distinct mechanisms. Overall, this multidisciplinary investigation illustrates a structure-mechanism-based strategy of tool invention for such a complicated brain disease.