Current Topics in Medicinal Chemistry - Volume 17, Issue 31, 2017

Alzheimer's Disease (AD) is a multifactorial and fatal neurodegenerative disorder affecting around 35 million people worldwide, which is characterized by decline of cholinergic function, deregulation of amyloid beta (Aβ) oligomers formation and Aβ fibril deposition. Multi-Target- Directed Ligands (MTDLs) have emerged as an original strategy for developing new therapeutic agents on AD. Multicomponent Reactions (MCRs) are a useful alternative to sequential multistep syntheses, allowing scaffold diversity and a rapid and easy access to biologically relevant compounds. The biological diversity of MCRs is very rich providing great possibilities for researchers interested in bioactive small molecular weight compounds. Since the MTDL strategy has been used to develop compounds endowed with the capacity to interact with different targets, versatile compound libraries may be obtained by MCRs according to the well established features of each target. Thus, either MTDLs or monotarget compounds have been developed by MCRs to address different factors implicated in AD. This work focuses on antioxidants, calcium channel modulators, both AChE and BuChE inhibitors, BACE1 inhibitors, and modulators of the nuclear factor (erythroid-derived 2)-like 2. First, we discuss the Biginelli reaction and its use for developing new interesting compounds for AD, followed by the contribution of Ugi reaction and, finally, the interest of other MCRs in the same topic.

Tacrine was the first drug to display beneficial effects on cognitive impairment of Alzheimer Disease (AD) patients. Unfortunately, many treated patients displayed related hepatotoxicity, and hence this drug was withdrawn. Notwithstanding, recent efforts have been directed to design small tacrine analogues targeting the underlying pathogenic mechanisms of AD. In this context, we have developed a number of pyranotacrines by changing the benzene fused ring in tacrine by a 4Hpyran. Based on this strategy, in this account we will show the tacrine analogues that we have designed, synthesized and evaluated as potential multipotent agents for AD in the last years. We have demonstrated that this approach is possible, and that a number of readily available tacrine analogues show cholinesterase inhibition power, as well as other pharmacological properties, such as calcium channel blockade, antioxidant properties, neuroprotection, Aβ-amyloid inhibition aggregation capacity, etc., making them suitable multipotent molecules for further development for the potential treatment of AD.

Alzheimer's Disease (AD) once considered a rare disorder emerges as a major health concern in recent times. The disease pathogenesis is very complex and yet to be understood completely. However, “Amyloid Cascade” is the central event in disease pathogenesis. Several proteins of the amyloid cascade are currently being considered as potential targets for AD therapeutics discovery. Many potential compounds are in clinical trials, but till now there is no known cure for the disease. Recent years have witnessed remarkable research interest in the search of novel concepts in drug designing for AD. Multi-targeted ligand design is a paradigm shift in conventional drug discovery. In this process rather than designing ligands targeting a single receptor, novel ligands have been designed/ synthesized that can simultaneously target many pathways involved in disease pathogenesis. Here, recent developments in computational drug designing protocols to identify multi-targeted ligand for AD have been discussed. Therapeutic potential of different multi-potent compounds also has been discussed briefly. Prime emphasis has been given to multi-potent ligand from natural resources. Polyphenols are an interesting group of compounds which show efficacy against a wide range of disease and have the property to exhibit multi-potency. Several groups attempted to identify novel multi-potent phytochemicals for AD therapy. Multi-potency of several polyphenols or compounds synthesized using the poly-phenolic scaffolds have been briefly discussed here. However, the multi-targeted drug designing for AD is still in early stages, more advancement in drug designing method/algorithm developments is urgently required to discover more efficient compounds for AD therapeutics.

Tacrine was the first drug approved by FDA (US) for the treatment of Alzheimer's disease suffering patients. Nowadays, this agent has been withdrawn from the clinics due to secondary effects, which, most importantly, include hepatotoxicity. However, the research on new tacrine analogues devoid of these therapeutically undesirable effects, but benefiting of their high and well known positive cholinergic power, has produced a number of new non-hepatotoxic tacrines. In this context, our laboratory has recently prepared a new set of heterocyclic tacrines by changing the benzene ring present in tacrine by appropriate heterocyclic motifs. Based on this approach, in this review we summarize the results that we have found in the ChromenoPyranoTacrines, one of the families of tacrine analogues. This highlights their pharmacological profile, such as their cholinesterase inhibition power, calcium channel blockade, antioxidant capacity, Aβ-anti-aggregating, and neuroprotective properties. As a result of this work we have identified permeable, neuroprotective MTD tacrines racemic hit-tacrines 11-amino-12-(3,4,5-trimethoxyphenyl)-7,9,10,12-tetrahydro-8H-chromeno[2,3- b]quinolin-3-ol (6g) and 14-(3,4-dimethoxyphenyl)-9,11,12,14-tetrahydro-10H-benzo[5,6] chromeno [2,3-b] quinolin-13-amine (7i),devoid of toxic effects and showing potent anti-cholinesterasic properties, that deserve attention and further development in order to find new, and more efficient drugs, for AD therapy.

In industrialized countries, Alzheimer's disease represents the most devastating neurodegenerative disorder in elderly people and the search for a disease modifying agent is still justified by this unmet need. Several possible targets have been explored to find an appropriate drug therapy, and in this review, dual inhibitors of beta secretase and glycogen synthase kinase 3, recently reported in literature, will be appraised. Applying a ligand-based approach, the triazinone core emerged as a suitable scaffold to simultaneously bind the aspartic dyad of BACE-1 and the ATP site of GSK-3β, leading to a series of small molecules endowed with a balanced micromolar affinity and a promising pharmacokinetic profile. Differently, by means of a structure-based approach, a series of well-balanced dual binding molecules were designed, taking advantage of the versatility of the curcumin scaffold. For some of these new compounds a potential neuroprotective effect was also observed, due to their ability to counteract the oxidative stress through the inhibition of NQO1 enzyme. Finally, different virtual screening analyses were performed, leading to the identification of new potential scaffolds deserving further development.

Alzheimer's Disease (AD) is a fatal neurodegenerative disorder, having a complex aetiology with numerous possible drug targets. There are targets that have been known for years while more new targets and theories have also emerged. Beta amyloid and cholinesterases are the most significant biological targets for finding curative treatment of AD. The major class of drugs used for AD till now has been the Cholinesterase (ChE) inhibitors. Other prevailing models of molecular pathogenesis in AD include Neurofibrillary Tangles (NFTs) and amyloid deposition, tryptophan degradation pathway, kinase and phosphatase activity imbalance and neuroinflammation. The beta amyloid aggregation initiates flow of events resulting in neurotoxicity and finally clinical pathogenesis of AD. Furthermore, ApoE is another very significant entity involved in repairing and maintaining the neurons and has important role in neurodegeneration. Neuroinflammation being the primmest symptom for AD is essential to focus on. Multiple factors and complexity in interlinking disease progression pose huge challenge to find one complete curing drug. With so many promising molecules having multiform pharmacological profile from all over the world however facing failures in clinical trials indicates the need to consider all aspects of the old as well as new therapeutic targets of AD. Until the disease mechanism is better understood, it is likely that multiple targeting, symptomatic and diseasemodifying, is the way forward. Most recent approaches to find anti-Alzheimer's agents have focused on multi-target directed agents that include targeting all glorious targets hypothesized against AD. New identification of prototype candidates that could be starting point of a new way of thinking drug design has been done and many drug candidates are under preclinical evaluation. The main focus of this review is to discuss the recent understanding of key targets and the development of potential therapeutic agents for the treatment of AD. It also documents the current therapeutic agents in clinical trials and under development based on their main mode of action.