Updated pharmaceutical progress on plant antibiotic rhein and its analogs: Bioactivities, structure-activity relationships and future perspectives

Rhein, as a plant antibiotic, demonstrates a broad spectrum of pharmacological effects. Nevertheless, its limited water solubility, low bioavailability, and potential hepatotoxicity and nephrotoxicity making it difficult to directly become a medicine, thereby imposing significant constraints on its clinical application. In recent decades, extensive researches have been proceeded on the multifaceted structural modifications of rhein, resulting in notable improvements on pharmacological activities and druggabilities. This review offers a comprehensive overview and advanced update on the biological potential and structural-activity relationships (SARs) of various rhein derivatives, delineating the sites of structural modification and corresponding activity trends of rhein derivatives for future.

Design, synthesis and biological evaluation of rhein-piperazine-furanone hybrids as potential anticancer agents

Novel rhein-piperazine-furanone hybrids, 5, were designed and synthesized efficiently from rhein. Cytotoxicity of all hybrids 5a-j against A549 human lung cancer cells was superior to the parent rhein and the reference cytarabine (CAR). Hybrid 5e (IC50 = 5.74 μM), the most potent compound, was 46- and 35-fold more toxic against A549 cells than rhein (IC50 = 265.59 μM) and CAR (IC50 = 202.57 μM), respectively. Moreover, hybrid 5e (IC50 = 69.28 μM) was less toxic to normal WI-38 human lung fibroblast cells with good selectivity (WI-38/A549, SI ≈ 12), being much higher than rhein (SI ≈ 1) and CAR (SI ≈ 2). Structure-activity relationship (SAR) analysis showed that cytotoxicity and selectivity against A549 lung cancer cells were greatly enhanced when methoxy-containing furanone was introduced to the hybrids (5e and 5h). Further, hybrid 5e showed better cytotoxicity against four types of human lung cancer cells (H460, A549, PC-9, and Calu-1; IC50 = 4.35-15.39 μM) than six other types of human cancer cells (SK-BR-3, SK-OV-3, 786-O, Huh-7, HCT116, and HeLa; IC50 = 13.77-60.45 μM), showing specificity. In particular, hybrid 5e showed the highest cytotoxicity (IC50 = 4.35 μM) and the highest selectivity (WI-38/H460, SI ≈ 16) against H460 human lung cancer cells. Flow cytometric analysis showed that hybrid 5e induced apoptosis in a concentration-dependent manner in H460 cells. The results show that the cytotoxicity and selectivity of rhein can be greatly enhanced by hybridization with furanone. Hybrid 5e is expected to be a leading candidate for anti-lung cancer drugs.

The potential of Rhein's aromatic amines for Parkinson's disease prevention and treatment: α-Synuclein aggregation inhibition and disaggregation of preformed fibers

The aggregation of α-Syn is a pivotal mechanism in Parkinson's disease (PD). Effectively maintaining α-Syn proteostasis involves both inhibiting its aggregation and promoting disaggregation. In this study, we developed a series of aromatic amide derivatives based on Rhein. Two of these compounds, 4,5-dihydroxy-N-(3-hydroxyphenyl)-9,10-dioxo-9,10-dihydroanthracene-2-carboxamide (a5) and 4,5-dihydroxy-N-(2-hydroxy-4-chlorophenyl)-9,10-dioxo-9,10-dihydroanthracene-2-carboxamide (a8), exhibited good binding affinities to α-Syn residues, demonstrating promising inhibitory activity against α-Syn aggregation in vitro, with low IC50 values (1.35 and 1.08 μM, respectivly). These inhibitors acted throughout the entire aggregation process by stabilizing α-Syn's conformation and preventing the formation of β-sheet aggregates. They also effectively disassembled preformed α-Syn oligomers and fibrils. Preliminary mechanistic insights indicated that they bound to the specific domain within fibrils, inducing fibril instability, collapse, and the formation of smaller aggregates and monomeric α-Syn units. This research underscores the therapeutic potential of Rhein's aromatic amides in targeting α-Syn aggregation for PD treatment and suggests broader applications in managing and preventing neurodegenerative diseases.

Latest advances in dual inhibitors of acetylcholinesterase and monoamine oxidase B against Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain disease characterised by progressive memory loss and cognition impairment, ultimately leading to death. There are three FDA-approved acetylcholinesterase inhibitors (donepezil, rivastigmine, and galantamine, AChEIs) for the symptomatic treatment of AD. Monoamine oxidase B (MAO-B) has been considered to contribute to pathologies of AD. Therefore, we reviewed the dual inhibitors of acetylcholinesterase (AChE) and MAO-B developed in the last five years. In this review, these dual-target inhibitors were classified into six groups according to the basic parent structure, including chalcone, coumarin, chromone, benzo-fused five-membered ring, imine and hydrazine, and other scaffolds. Their design strategies, structure-activity relationships (SARs), and molecular docking studies with AChE and MAO-B were analysed and discussed, giving valuable insights for the subsequent development of AChE and MAO-B dual inhibitors. Challenges in the development of balanced and potent AChE and MAO-B dual inhibitors were noted, and corresponding solutions were provided.

Quinones as Neuroprotective Agents

Quinones can in principle be viewed as a double-edged sword in the treatment of neurodegenerative diseases, since they are often cytoprotective but can also be cytotoxic due to covalent and redox modification of biomolecules. Nevertheless, low doses of moderately electrophilic quinones are generally cytoprotective, mainly due to their ability to activate the Keap1/Nrf2 pathway and thus induce the expression of detoxifying enzymes. Some natural quinones have relevant roles in important physiological processes. One of them is coenzyme Q₁₀, which takes part in the oxidative phosphorylation processes involved in cell energy production, as a proton and electron carrier in the mitochondrial respiratory chain, and shows neuroprotective effects relevant to Alzheimer's and Parkinson's diseases. Additional neuroprotective quinones that can be regarded as coenzyme Q₁₀ analogues are idobenone, mitoquinone and plastoquinone. Other endogenous quinones with neuroprotective activities include tocopherol-derived quinones, most notably vatiquinone, and vitamin K. A final group of non-endogenous quinones with neuroprotective activity is discussed, comprising embelin, APX-3330, cannabinoid-derived quinones, asterriquinones and other indolylquinones, pyrroloquinolinequinone and its analogues, geldanamycin and its analogues, rifampicin quinone, memoquin and a number of hybrid structures combining quinones with amino acids, cholinesterase inhibitors and non-steroidal anti-inflammatory drugs.

Identification of a Novel Dual Inhibitor of Acetylcholinesterase and Butyrylcholinesterase: In Vitro and In Silico Studies

The enhancement of cholinergic functions via acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition is considered a valuable therapeutic strategy for the treatment of Alzheimer's disease. This study aimed to evaluate the in vitro effect of ZINC390718, previously filtered using computational approaches, on both cholinesterases and to characterize, using a molecular dynamics (MD) simulation, the possible binding mode of this compound inside the cholinesterase enzymes. The in vitro cytotoxicity effect was also investigated using a primary astrocyte-enriched glial cell culture. ZINC390718 presented in vitro dual inhibitory activity against AChE at a high micromolar range (IC₅₀ = 543.8 µM) and against BuChE (IC₅₀ = 241.1 µM) in a concentration-dependent manner, with greater activity against BuChE. The MD simulation revealed that ZINC390718 performed important hydrophobic and H-bond interactions with the catalytic residue sites on both targets. The residues that promoted the hydrophobic interactions and H-bonding in the AChE target were Leu67, Trp86, Phe123, Tyr124, Ser293, Phe295, and Tyr341, and on the BuChE target, they were Asp70, Tyr332, Tyr128, Ile442, Trp82, and Glu197. The cytotoxic effect of Z390718, evaluated via cell viability, showed that the molecule has low in vitro toxicity. The in vitro and in silico results indicate that ZINC390718 can be used as chemotype for the optimization and identification of new dual cholinesterase inhibitors.

Visible light photocatalysis in the synthesis of pharmaceutically relevant heterocyclic scaffolds

Visible light and photoredox catalysis have emerged as a powerful and long-lasting tool for organic synthesis, demonstrating the importance of a variety of chemical bond formation methods.

Rhein Derivatives, A Promising Pivot?

Rhein, an anthraquinone derivative, has been employed widely, especially for the treatment of intractable diseases like diabetic nephropathy, arthritis, and cancer in a unique action mechanism. In the last decades, considerable efforts have been made in structural modification of rhein. This paper reviewed patents on pharmacological activity and therapeutic application of rhein and its derivatives from 1978 to 2018. Particularly, an analysis of patents was made, with the top 10 most valuable patents presented, and the interpretation of the legal status of patents was given. Given the properties of superior pharmacological activity, rich resources, cheap price, low toxicity, and mature extraction process, it is believed that an in-depth investigation on rhein and its derivatives is worth trying.

Design and synthesis of novel 3,4-dihydrocoumarins as potent and selective monoamine oxidase-B inhibitors with the neuroprotection against Parkinson's disease

The monoamine oxidase-B (MAO-B) inhibitors with neuroprotective effects are better for Parkinson's disease (PD) treatment, due to the complicated pathogenesis of PD. To develop new hMAO-B inhibitors with neuroprotection, a novel series of 3,4-dihydrocoumarins was designed as selective and reversible hMAO-B inhibitors to treat PD. Most compounds showed potent and selective inhibition for hMAO-B over hMAO-A with IC₅₀ values ranging from nanomolar to sub-nanomolar. Among them, compound 4d was the most potent hMAO-B inhibitor (IC₅₀ = 0.37 nM) being about 20783-fold more active than iproniazid, and exhibited the highest selectivity for hMAO-B (SI > 270,270). Kinetic studies revealed that compound 4d was a reversible and competitive inhibitor of hMAO-B. Neuroprotective studies indicated that compound 4d could protect PC12 cells from the damage induced by 6-OHDA and rotenone. Besides, compound 4d did not exhibit acute toxicity at a dose up to 2500 mg/kg (po), and could cross the BBB in parallel artificial membrane permeability assay. More importantly, compound 4d was able to significantly prevent the motor deficits in the MPTP-induced PD model. These results indicate that compound 4d is an effective and promising candidate against PD.

Journey on Naphthoquinone and Anthraquinone Derivatives: New Insights in Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that is characterized by memory loss, cognitive impairment, and functional decline leading to dementia and death. AD imposes neuronal death by the intricate interplay of different neurochemical factors, which continue to inspire the medicinal chemist as molecular targets for the development of new agents for the treatment of AD with diverse mechanisms of action, but also depict a more complex AD scenario. Within the wide variety of reported molecules, this review summarizes and offers a global overview of recent advancements on naphthoquinone (NQ) and anthraquinone (AQ) derivatives whose more relevant chemical features and structure-activity relationship studies will be discussed with a view to providing the perspective for the design of viable drugs for the treatment of AD. In particular, cholinesterases (ChEs), β-amyloid (Aβ) and tau proteins have been identified as key targets of these classes of compounds, where the NQ or AQ scaffold may contribute to the biological effect against AD as main unit or significant substructure. The multitarget directed ligand (MTDL) strategy will be described, as a chance for these molecules to exhibit significant potential on the road to therapeutics for AD.

Design, Synthesis and Biological Evaluation of New Cycloalkyl Fused Quinolines Tethered to Isatin Schiff Bases as Cholinesterase Inhibitors

AIMS AND OBJECTIVE

Alzheimer's disease is now a most prevalent neuro degenerative disease of central nervous system leading to dementia in elderly aged population. Numerous pathological changes have been associated in the progression of Alzheimer's disease. One of such pathological hypothesis is declined cholinergic activity which eventually affects cognitive and memory deficits. Inhibition cholinesterases will apparently elevate acetyl choline levels which is benefactor on cognitive symptoms of the disease. This manuscript describes the new tacrine derivatives tethered to isatin Schiff bases through alkanoyl linker and screened for cholinesterase inhibitory activity.

MATERIALS AND METHODS

Tacrine and two more cycloalkyl ring fused quinolones were synthesized and converted to Ncycloalkyl fused quinoline chloroamides. Isatin Schiff bases were also synthesized by the reaction between isatin and substituted aromatic anilines and in subsequent reaction, isatin Schiff bases were reacted with cycloalkyl fused quinolones to afford anticipated compounds 10a-i, 11a-i and 12a-i. All the compounds have been screened for acetyl and butyryl cholinesterase inhibitory activity and in vivo behavioral studies. Binding interactions of the desired compounds have also been studied by docking them in active site of both cholinesterases.

RESULTS

Three compounds 12d, 12e and 12h with propionyl and butyroyl linker between amine and isatin Schiff base scaffold have shown potent acetyl and butyryl cholinesterase inhibitory activity. However most potent cholinesterase inhibitor was 13d with IC50 value of 0.71±0.004 and 1.08±0.02 μM against acetyl and butyryl cholinesterases respectively. The hepatotoxicity of potent compounds revealed that the tested compounds were less hepatotoxic than tacrine and also exhibited encouraging in vivo behavioral studies in test animals. Docking studies of all the molecules disclosed close hydrogen bond interactions within the binding site of both cholinesterases.

CONCLUSION

New cycloalkyl fused quinolones tethered with alkoyl linker to isatin Schiff bases endowed significant and potent cholinesterase inhibitory activities. Few of the compounds have also exhibited lesser hepatotoxicity and all the synthesized compounds were good in behavioral studies. Molecular docking studies also indicated close interactions in active site of cholinesterases.

Tacrine-Natural-Product Hybrids for Alzheimer's Disease Therapy

Alzheimer's disease (AD) is a complex, neurodegenerative pathology showing, among others, high cholinergic and neurotransmitter deficits, oxidative stress, inflammation, Aβ-aggregation resulting in senile plaques formation, and hyperphosphorylation of tau-protein leading to neurofibrillary tangles. Due to its multifactorial and complex nature, multitarget directed small-molecules able to simultaneously inhibit or bind diverse biological targets involved in the progress and development of AD are considered now the best therapeutic strategy to design new compounds for AD therapy. Among them, tacrine is a very well known standard-gold ligand, and natural products have been a traditional source of new agents for diverse therapeutic treatments. In this review, we will update recent developments of multitarget tacrinenatural products hybrids for AD therapy.

Chromone and donepezil hybrids as new multipotent cholinesterase and monoamine oxidase inhibitors for the potential treatment of Alzheimer's disease

A series of chromone and donepezil hybrids were designed, synthesized, and evaluated as multipotent cholinesterase (ChE) and monoamine oxidase (MAO) inhibitors for the potential therapy of Alzheimer's disease (AD). In vitro studies showed that the great majority of these compounds exhibited potent inhibitory activity toward BuChE and AChE and clearly selective inhibition for hMAO-B. In particular, compound 5c presented the most balanced potential for ChE inhibition (BuChE: IC₅₀ = 5.24 μM; AChE: IC₅₀ = 0.37 μM) and hMAO-B selectivity (IC₅₀ = 0.272 μM, SI = 247). Molecular modeling and kinetic studies suggested that 5c was a mixed-type inhibitor, binding simultaneously to peripheral and active sites of AChE. It was also a competitive inhibitor, which occupied the substrate and entrance cavities of MAO-B. Moreover, compound 5c could penetrate the blood-brain barrier (BBB) and showed low toxicity to rat pheochromocytoma (PC12) cells. Altogether, these results indicated that compound 5c might be a hopeful multitarget drug candidate with possible impact on Alzheimer's disease therapy.

Aryldiazoquinoline based multifunctional small molecules for modulating Aβ42aggregation and cholinesterase activity related to Alzheimer's disease

Novel series of aryldiazoquinoline multifunctional molecules controls amyloid formation and neuro-protective role by inhibiting esterase enzymes.

Combining Chalcones with Donepezil to Inhibit Both Cholinesterases and Aβ Fibril Assembly

The fact that the number of people with Alzheimer's disease is increasing, combined with the limited availability of drugs for its treatment, emphasize the need for the development of novel effective therapeutics for treating this brain disorder. Herein, we focus on generating 12 chalcone-donepezil hybrids, with the goal of simultaneously targeting amyloid-β (Aβ) peptides as well as cholinesterases (i.e., acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)). We present the design, synthesis, and biochemical evaluation of these two series of novel 1,3-chalcone-donepezil (15a-15f) or 1,4-chalcone-donepezil (16a-16f) hybrids. We evaluate the relationship between their structures and their ability to inhibit AChE/BChE activity as well as their ability to bind Aβ peptides. We show that several of these novel chalcone-donepezil hybrids can successfully inhibit AChE/BChE as well as the assembly of N-biotinylated Aβ(1-42) oligomers. We also demonstrate that the Aβ binding site of these hybrids differs from that of Pittsburgh Compound B (PIB).

Design, synthesis and biological activity of novel tacrine-isatin Schiff base hybrid derivatives

A series of novel tacrine-isatin Schiff base hybrid derivatives (7a-p) were designed, synthesized and evaluated as multi-target candidates against Alzheimer's disease (AD). The biological assays indicated that most of these compounds displayed potent inhibitory activity toward acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) and specific selectivity for AChE over BuChE. It was also found that they act as excellent metal chelators. The compounds 7k and 7m were found to be good inhibitors of AChE-induced amyloid-beta (Aβ) aggregation. Most of the compounds inhibited AChE with the IC₅₀ values, ranging from 0.42 nM to 79.66 nM. Amongst them, 7k, 7m and 7p, all with a 6 carbon linker between tacrine and isatin Schiff base exhibited the strongest inhibitory activity against AChE with IC₅₀ values of 0.42 nM, 0.62 nM and 0.95 nM, respectively. They were 92-, 62- and 41-fold more active than tacrine (IC₅₀ = 38.72 nM) toward AChE. Most of the compounds also showed a potent BuChE inhibition among which 7d with an IC₅₀ value of 0.11 nM for BuChE is the most potent one (56-fold more potent than that of tacrine (IC₅₀ = 6.21 nM)). In addition, most compounds exhibited the highest metal chelating property. Kinetic and molecular modeling studies revealed that 7k is a mixed-type inhibitor, capable of binding to catalytic and peripheral site of AChE. Our findings make this hybrid scaffold an excellent candidate to modify current drugs in treating Alzheimer's disease (AD).

Neuroprotective Effects of Anthraquinones from Rhubarb in Central Nervous System Diseases

Rhubarb is a well-known traditional Chinese medicine; it has been used in China for thousands of years. Rhubarb anthraquinones are the major medicinal ingredients derived from rhubarb including emodin, aloe-emodin, chrysophanol, rhein, physcion, and danthron. These different anthraquinone derivatives alone or in combination play a therapeutic role in central nervous system diseases (CNSD), such as cerebral ischemic stroke, intracerebral hemorrhage, traumatic brain injury, brain tumor, Alzheimer's disease, depression, and others. We review the experimental studies on these six anthraquinones in the treatment of CNSD by consulting literature published in the last 20 years in PubMed and then give a future perspective on it. In the end of this paper some deficiencies related to these studies also have been pointed out.

Design, synthesis and evaluation of a novel metal chelator as multifunctional agents for the treatment of Alzheimer's disease

A series of compounds following the lead compounds including deferasirox and tacrine were designed, synthesized and evaluated as multifunctional agents against Alzheimer's disease (AD). In vitro studies showed that most synthesized compounds exhibited good multifunctional activities in inhibiting acetylcholinesterase (bAChE), and chelating metal ions. Especially, compound TD_e demonstrated significant metal chelating property, a moderate acetylcholinesterase (AChE) inhibitory activity and an antioxidant activity. Results from the molecular modeling indicated that TD compounds were mixed-type inhibitor, binding simultaneously to the catalytic anionic site (CAS) and the peripheral anionic site (PAS) of TcAChE. Moreover, TD_e showed a low cytotoxicity but a good protective activity against the injury caused by H₂O₂. These results suggest that TD compounds might be considered as attractive multi-target cholinesterase inhibitor and will play important roles in the treatment of AD.

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.

Synthesis and bioevaluation of new tacrine-cinnamic acid hybrids as cholinesterase inhibitors against Alzheimer's disease

Small molecule cholinesterases inhibitor (ChEI) provides an effective therapeutic strategy to treat Alzheimer's disease (AD). Currently, the discovery of new ChEI with multi-target effect is still of great importance. Herein, we report the synthesis, structure-activity relationship study and biological evaluation of a series of tacrine-cinnamic acid hybrids as new ChEIs. All target compounds are evaluated for their in vitro cholinesterase inhibitory activities. The representatives which show potent activity on cholinesterase, are evaluated for the amyloid β-protein self-aggregation inhibition and in vivo assays. The optimal compound 19, 27, and 30 (human AChE IC₅₀ = 10.2 ± 1.2, 16.5 ± 1.7, and 15.3 ± 1.8 nM, respectively) show good performance in ameliorating the scopolamine-induced cognition impairment and preliminary safety in hepatotoxicity evaluation. These compounds deserve further evaluation for the development of new therapeutic agents against AD.

Design, synthesis and evaluation of novel cinnamic acid derivatives bearing N-benzyl pyridinium moiety as multifunctional cholinesterase inhibitors for Alzheimer's disease

A novel family of cinnamic acid derivatives has been developed to be multifunctional cholinesterase inhibitors against AD by fusing N-benzyl pyridinium moiety and different substituted cinnamic acids. In vitro studies showed that most compounds were endowed with a noteworthy ability to inhibit cholinesterase, self-induced Aβ (1–42) aggregation, and to chelate metal ions. Especially, compound 5l showed potent cholinesterase inhibitory activity (IC₅₀, 12.1 nM for eeAChE, 8.6 nM for hAChE, 2.6 μM for eqBuChE and 4.4 μM for hBuChE) and the highest selectivity toward AChE over BuChE. It also showed good inhibition of Aβ (1–42) aggregation (64.7% at 20 μM) and good neuroprotection on PC12 cells against amyloid-induced cell toxicity. Finally, compound 5l could penetrate the BBB, as forecasted by the PAMPA-BBB assay and proved in OF1 mice by ex vivo experiments. Overall, compound 5l seems to be a promising lead compound for the treatment of Alzheimer’s diseases.

Design, synthesis and multitarget biological profiling of second-generation anti-Alzheimer rhein-huprine hybrids

AIM

Simultaneous modulation of several key targets of the pathological network of Alzheimer's disease (AD) is being increasingly pursued as a promising option to fill the critical gap of efficacious drugs against this condition.

MATERIALS & METHODS

A short series of compounds purported to hit multiple targets of relevance in AD has been designed, on the basis of their distinct basicities estimated from high-level quantum mechanical computations, synthesized, and subjected to assays of inhibition of cholinesterases, BACE-1, and Aβ42 and tau aggregation, of antioxidant activity, and of brain permeation.

RESULTS

Using, as a template, a lead rhein-huprine hybrid with an interesting multitarget profile, we have developed second-generation compounds, designed by the modification of the huprine aromatic ring. Replacement by [1,8]-naphthyridine or thieno[3,2-e]pyridine systems resulted in decreased, although still potent, acetylcholinesterase or BACE-1 inhibitory activities, which are more balanced relative to their Aβ42 and tau antiaggregating and antioxidant activities.

CONCLUSION

Second-generation naphthyridine- and thienopyridine-based rhein-huprine hybrids emerge as interesting brain permeable compounds that hit several crucial pathogenic factors of AD.

Synthesis and pharmacological evaluation of novel chromone derivatives as balanced multifunctional agents against Alzheimer's disease

In a continuing effort to develop multitargeted compounds as potential treatment agents against Alzheimer's disease (AD), a series of chromone derivatives were designed, synthesized and evaluated. In vitro assay indicated that most of the target compounds have both MAOs inhibition activities, antioxidant activity and biometal chelating ability. Especially, compound s19 exhibits good inhibitory potency for inhibition of MAOs (IC₅₀ value of 5.12μM for hMAO-A and 0.816μM for hMAO-B), moderate inhibition of Aβ aggregation (75.1% at 20μM), metal chelation, control of ROS generation and antioxidant activity (ORAC=3.62). In addition, s19 could reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Taken together, these results suggested that s19 might be a promising multitargeted compound for AD treatment.

Recent progress in the identification of selective butyrylcholinesterase inhibitors for Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disorders with notable factor of dysfunction in cholinergic system. Low ACh level can be observed in the pathogenesis of AD. Several AChE inhibitors have already been used for clinical treatments. However, other than normal conditions, ACh is mostly hydrolyzed by BuChE in progressed AD. Account for an increased level of BuChE and decreased level of AChE in the late stage of AD, development of selective BuChE inhibitor is of vital importance. Up till now, compounds with various scaffolds have been discovered to selectively inhibit BuChE. Different effective anti-BuChE molecules are concluded in this review.

Novel multitarget-directed tacrine derivatives as potential candidates for the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is complex and progressive; it has not only threatened the health of elderly people, but also burdened the whole social medical and health system. The available therapy for AD is limited and the efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the design and development of efficacious and safe anti-AD agents has become a hotspot in the field of pharmaceutical research. Due to the multifactorial etiology of AD, the multitarget-directed ligands (MTDLs) approach is promising in search for new drugs for AD. Tacrine, which is the first acetylcholinesterase (AChE) inhibitor, has been selected as the ideal active fragment because of its simple structure, clear activity, and its superiority in the structural modification, thus it could be introduced into the overall molecular skeletons of the multi-target-directed anti-AD agents. In this review, we have summarized the recent advances (2012 to the present) in the chemical modification of tacrine, which could provide the reference for the further study of novel multi-target-directed tacrine derivatives to treat AD.

Design, synthesis, in vitro and in vivo evaluation of tacrine–cinnamic acid hybrids as multi-target acetyl- and butyrylcholinesterase inhibitors against Alzheimer's disease

A series of tacrine–cinnamic acid hybrids are synthesized as multi-target cholinesterase inhibitors against Alzheimer's disease.

Facile access to functionalized indenes and fused quinolines by regioselective 5-enolexo-dig Michael addition and cyclization reactions

Herein we report a facile approach to synthesise multi-substituted indenes and cyclopenta[b]quinolines under mild conditions.

Naphthoquinone-Tryptophan Hybrid Inhibits Aggregation of the Tau-Derived Peptide PHF6 and Reduces Neurotoxicity

Tauopathies, such as Alzheimer's disease (AD), are a group of disorders characterized neuropathologically by intracellular toxic accumulations of abnormal protein aggregates formed by misfolding of the microtubule-associated protein tau. Since protein self-assembly appears to be an initial key step in the pathology of this group of diseases, intervening in this process can be both a prophylactic measure and a means for modifying the course of the disease for therapeutic purposes. We and others have shown that aromatic small molecules can be effective inhibitors of aggregation of various protein assemblies, by binding to the aromatic core in aggregation-prone motifs and preventing their self-assembly. Specifically, we have designed a series of small aromatic naphthoquinone-tryptophan hybrid molecules as candidate aggregation inhibitors of β -sheet based assembly and demonstrated their efficacy toward inhibiting aggregation of the amyloid-β peptide, another culprit of AD, as well as of various other aggregative proteins involved in other protein misfolding diseases. Here we tested whether a leading naphthoquinone-tryptophan hybrid molecule, namely NQTrp, can be repurposed as an inhibitor of the aggregation of the tau protein in vitro and in vivo. We show that the molecule inhibits the in vitro assembly of PHF6, the aggregation-prone fragment of tau protein, reduces hyperphosphorylated tau deposits and ameliorates tauopathy-related behavioral defect in an established transgenic Drosophila model expressing human tau. We suggest that NQTrp, or optimized versions of it, could act as novel disease modifying drugs for AD and other tauopathies.

Recent progress in repositioning Alzheimer's disease drugs based on a multitarget strategy

Alzheimer's disease (AD) is a serious progressive neurological disorder, characterized by impaired cognition and profound irreversible memory loss. The multifactorial nature of AD and the absence of a cure so far have stimulated medicinal chemists worldwide to follow multitarget drug-design strategies based on repositioning approved drugs. This review describes a summary of recently published works focused on tailoring new derivatives of US FDA-approved acetylcholinesterase inhibitors, in addition to huperzine (a drug approved in China), either by hybridization with other pharmacophore elements (to hit more AD targets), or by combination of two FDA-approved drugs. Besides the capacity for improving the cholinergic activity, these polyfunctional derivatives are also able to tackle other important neuroprotective properties, such as anti-β-amyloid aggregation, scavenging of radical oxygen species, modulation of redox-active metals or inhibition of monoamine oxidase, thereby resulting in potentially novel and more effective therapeutics for the treatment of AD.

Rational modification of donepezil as multifunctional acetylcholinesterase inhibitors for the treatment of Alzheimer's disease

A series of novel donepezil derivatives was designed, synthesized and evaluated as multifunctional acetylcholinesterase (AChE) inhibitors for the treatment of Alzheimer's disease (AD). The screening results indicated that most of the compounds exhibited potent inhibition of AChE with IC50 values in the nanomolar range. Moreover, these derivatives displayed good antioxidant, Aβ interaction, blood-brain barrier penetration (PAMPA-BBB+) and ADMET properties (in silico). Among them, 5c demonstrated excellent AChE inhibition (IC50: 85 nM for eeAChE, 73 nM for hAChE), metal chelation, and inhibitory effects on self-induced, hAChE-induced and Cu(2+)-induced Aβ1-42 aggregation (18.5%, 72.4% and 46.3%, at 20 μM). Kinetic analysis and molecular modeling studies suggested that 5c could bind simultaneously to the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. More importantly, 5c exhibited significant neuroprotective potency against Aβ1-42-induced PC12 cell injury. Furthermore, the step-through passive avoidance test showed 5c significantly reversed scopolamine-induced memory deficit and no hepatotoxicity in mice. These results indicated that 5c might be a promising drug candidate for AD therapy.

Synthesis and pharmacological evaluation of donepezil-based agents as new cholinesterase/monoamine oxidase inhibitors for the potential application against Alzheimer's disease

In a continuing effort to develop multitargeted compounds as potential treatment agents against Alzheimer's disease (AD), a series of donepezil-like compounds were designed, synthesized and evaluated. In vitro studies showed that most of the designed compounds displayed potent inhibitory activities toward AChE, BuChE, MAO-B and MAO-A. Among them, w18 was a promising agent with balanced activities, which exhibited a moderate cholinesterase inhibition (IC₅₀, 0.220 μM for eeAChE; 1.23 μM for eqBuChE; 0.454 μM for hAChE) and an acceptable inhibitory activity against monoamine oxidases (IC₅₀, 3.14 μM for MAO-B; 13.4 μM for MAO-A). Moreover, w18 could also be a metal-chelator, and able to cross the blood-brain barrier with low cell toxicity on PC12 cells. Taken together, these results suggested that w18 might be a promising multitargeted compound for AD treatment.

Lecithin-gold hybrid nanocarriers as efficient and pH selective vehicles for oral delivery of diacerein-In-vitro and in-vivo study

We report the synthesis and evaluation of lecithin-gold hybrid nanocarriers for the oral delivery of drugs with improved pharmacokinetics, Au-drug interactive bioactivity and controlled drug releasing behavior at physiological pH inside human body. For this purpose, diacerein, a hydrophobic anti-arthritic drug, was loaded in lecithin NPs (LD NPs), which were further coated by Au NPs either by in-situ production of Au NPs on LD NPs or by employing pre-synthesized Au NPs. All LDAu NPs were found to release drug selectively at the physiological pH of 7.4 and showed 2.5 times increase in the oral bioavailability of diacerein. Pharmacological efficacy was significantly improved i.e., greater than the additive effect of diacerein and Au NPs alone. LDAu NPs started suppressing inflammation at first phase, whereas LD NPs showed activity in the second phase of inflammation. These results indicate the interaction of Au NPs with prostaglandins and histaminic mediators of first phase of carrageenan induced inflammation. Acute toxicity study showed no hepatic damage but the renal toxicity parameters were close to the upper safety limits. Toxicity parameters were dependent on surface engineering of LDAu NPs. Apart from enhancing the oral bioavailability of hydrophobic drugs and improving their anti-inflammatory activity, these hybrid nanocarriers may have potential applications in gold-based photothermal therapy and the tracing of inflammation at atherosclerotic and arthritic site.