Current Topics in Medicinal Chemistry - Volume 15, Issue 17, 2015

The serotonin 5-HT6 receptor (5- HT6R) is amongst the recently discovered serotonergic receptors with almost exclusive localization in the brain. Hence, this receptor is fast emerging as a promising target for cognition enhancement in central nervous system (CNS) diseases such as Alzheimer’s disease (cognitive function), obesity, schizophrenia and anxiety. The last decade has seen a surge of literature reports on the functional role of this receptor in learning and memory processes and investigations related to the chemistry and pharmacology of 5-HT6 receptor ligands, especially 5- HT6 receptor antagonists. Studies show the involvement of multiple neurotransmitter systems in cognitive enhancement by 5-HT6R antagonists including cholinergic, glutamatergic, and GABAergic systems. Several of the 5-HT6R ligands are indole based agents bearing structural similarity to the endogenous neurotransmitter serotonin. Based on the pharmacophoric models proposed for these agents, drug designing has been carried out incorporating various heterocyclic replacements for the indole nucleus. In this review, we have broadly summarized the medicinal chemistry and current status of this fairly recent class of drugs along with their potential therapeutic applications.

Curcumin, a natural yellow polyphenol, is isolated from the herb Curcuma longa L. (turmeric), a member of the ginger family. It has been extensively studied due to their multiple pharmacological properties. Nevertheless, curcumin has disadvantages such as poor water solubility, poor bioavailability and rapid metabolism, which has prompted the search for analogues that overcome these shortcomings while maintaining or improving their good pharmacological properties. Among the main curcumin analogues that have been developed, the heterocyclic curcuminoids show a high interest. In this review, we describe recent progress in the synthesis and pharmacological properties of new heterocyclic curcumin derivatives. The most recent developments in anti-cancer, anti-Alzheimer, anti-bacterial and anti-oxidants heterocyclic curcumin derivatives are covered.

Cholinesterase inhibition is the only current validated target in clinics in the treatment of Alzheimer’s disease (AD). Therefore, there is continuous interest in the development and discovery of novel cholinesterase inhibitory molecules. Coumarins, beside their employment in other pharmacological groups, have also attracted attention to be utilized in cholinesterase inhibitory molecule discovery and development. Numerous studies so far indicated the natural and synthetic coumarin analogues that have the potential to inhibit acetylcholinesterase and butyrylcholinesterase enzymes. Since the pathophysiology of AD is highly complex and, in particular, monoamine oxidase (MAO) inhibitors are also utilized in clinic for disease symptoms, coumarin analogues, either natural or synthetic, that have the potential to inhibit cholinesterase or MAO enzymes are summarized within this review.

Plants are one of the most important resources for the discovery of new drugs. The potential of natural compounds as new drug leads is clearly illustrated by the discovery and development of many modern medicines. This is an encouraging factor that drives natural products research in the vegetable kingdom. Neocryptolepine is a tetracyclic nitrogen heterocycle isolated from the African climber Cryptolepis sanguinolenta, which is widely used in traditional African medicine in many countries of Central and West Africa. The natural product is one of the representative examples of the small family of indolo[2,3-b]quinoline alkaloids, being endowed of multiple biological activities, including DNA-binding and inhibition of the enzyme topoisomerase II. It is also cytotoxic, antibacterial, antifungal and molluscicidal, also displaying antiprotozoal activity, particularly as antitrypanosomal, antileishmanial, antischistosomal and antiplasmodial. Some of these activities have been related to the product’s ability to bind to DNA and to inhibit topoisomerase II; however, the exact mechanisms behind all of the observed bioactivities have not been comprehensively clarified. Major research activities regarding neocryptolepine have been focused into two seemingly opposite fields, related to its cytotoxic and antimalarial properties. Optimization of the natural product as a cytotoxic agent implied improvements in its bioavailability and activity, while the need of non-cytotoxic compounds guided the design and optimization of antimalarial agents. Therefore, the aim of the present article is to systematically review the current knowledge about the diversity of the biological activities related to neocryptolepine, its analogs and derivatives.

A growing number of studies have revealed that natural molecules own interesting antioxidant and anti-apoptotic properties in cell culture as well as in animal models of human diseases such as cancer, inflammatory and neurodegenerative diseases. During the past sixty years, several cucurbitacins have been isolated from a number of cucurbitaceous species, amongst others. Cucurbitacins are triterpenoid compounds originally identify as the bitter components of the Cucurbit family that demonstrated several pro-survival activities in various model of cellular decay. Specifically, Cucurbitacin E (CuE), an oxygenated tetracyclic triterpenoid, has been investigated in a wider array of bioactivities, mainly immunomodulatory. Recently, CuE has been reported to possess anti-inflammatory and anti-tumorigenic properties mediated by its action on the cellular cytoskeleton, on mitotic pathways as well as on cellular autophagy. Few studies also pinpoint the role of CuE in the nervous system as cytostatic for gliomas and neuroprotective in a model of Parkinson’s diseases. This review deals with the use of CuE in various experimental models as one of the most promising therapeutic natural molecules against cancer proliferation, as an immunomudulator and for the prevention of neurodegeneration.

In last decades, diet and dietary components have been regarded as important strategies to prevent the development or mitigate numerous chronic diseases, including inflammation, cardiovascular pathologies, cancer, etc. One of the most common dietary components of Asian population is soy. A plethora of research shows the promising effect of soy soy-based foodstuffs and genistein, which is one of the predominant isoflavone compounds, in the prevention and mitigation of stroke. Growing evidence shows that genistein, which is a selective estrogen receptor modulator, mitigates ischemic stroke-induced damages through the modification of oxidative stress and molecular pathways. The promising pharmacological role of genistein is attributed to its ability to suppress nuclear factor (NF)-kappa B and Akt signaling pathway, direct antioxidant action, and targeting estrogen and androgen-mediated molecular pathways which help to mitigate stroke damages and prolong cell survival. In this work, we systematically review the current reports on the therapeutic role of genistein against ischemic stroke and its molecular mechanism of actions.

Piperine is the main constituent of pepper, a commonly used kitchen spice and has been reported to possess various pharmacological activities. The structural features, an aromatic ring with a methylenedioxy bridge, a conjugated dienone system and a piperidine ring constituting an amide bond, possessed by the molecule have been considered important for the molecule to exhibit an array of bioactivities. Several modifications of above structural units have affected the biological properties of piperine, either enhancing or in some cases completely abolishing the activity. The present review emphasizes on the synthetic aspects of piperine along with the structure-activity relationships of its derivatives so as to rationalize the discovery of newer piperine based molecules.

Quercetin, a prominent dietary antioxidant present in vegetables, especially onions, fruits, highlighting apples and berries, wine and tea, belongs to a group of plant derived heterocyclic polyphenols. These compounds could be important mediators of the biological actions attributed to healthy diets. Chemically, quercetin is a type of flavonoid that specifically belongs to the flavonols group. It naturally occurs either as glycoside or aglycone, both of which have biological activity. Many of the natural sources of quercetin are included in the Mediterranean diet, a dietary habit associated with a decrease of cardiovascular diseases. During the last years, several researches have reported effects consistent with pharmacological applications of quercetin in cardiovascular diseases, such as atherosclerosis, ischemia-reperfusion injury, cardiotoxicity, and hypertension, among others. In this review, the pathways and molecules involved in the beneficial effects of quercetin are summarized. In addition, a scope of the new insights concerning quercetin pharmacokinetics, pharmacodynamics and bioavailability are presented. The mechanisms whereby quercetin exerts its effects have not been fully elucidated. However, interesting results have been obtained from early clinical studies involving cardioprotection by quercetin, but much knowledge is still lacking in the field of its bioavailability to improve the clinical application of this flavonol. This study presents evidence supporting the point of view that quercetin should be considered a potential therapeutic agent against cardiovascular diseases, giving rise to novel applications in their prevention and treatment.

Phytochemical investigation of Azorella madreporica led to the isolation of four known compounds and an unknown chalcone. The structure of the new compound was identified by spectroscopy, including two-dimensional NMR techniques and comparison with published spectral data. The antioxidant activity of chalcone (compound 1) was measured using the 1,2-diphenyl-2-picryl-hydrazyl (DPPH) free radical scavenging assay, and the bioactivity was evaluated against five bacteria (Mycobacterium smegmatis ATCC 14468, clinical isolates of Staphylococcus aureus, Klebsiella granulomatis, Morganella morganii and Escherichia coli) and four cancer cell lines. Docking studies with the tested cancer related proteins revealed nearby values of energy between doxorubicin and compound 1. Besides, protein-ligand interactions correlate with these energy values.

Anxiety is one of the behavior disorders that has been studied more together with depression in the world, and that has enormous interference in the mental health of the affected patients. The states of panic and phobia are a part of the psychological characteristics that some drugs have tried to control though with varied side effects that are proven to be difficult to control. The use of perimidinone derivatives against the effects of anxiety has generated that A5 is the most active and selective anxiolytic compound, differing with regard to diazepam (DZP) used as control reference in elevated plus-maze (EPM) test. This test allows to conclude that it is feasible to differentiate the use selective as anxiolytic or antidepressant of certain perimidinones, because A4 had been characterized by our research group as an important antidepressant respect to A5 studied in previous reports.

Nature is an ancient pharmacy that is largely used as an inspiring source for drug discovery processes for the early eras. Several drugs used nowadays are of natural product origin or inspired on the basis of natural product structures and approximately half of the 20 best-selling non-protein drugs are related to natural products. However, a largely unexplored marine world that presumably harbors the most biodiversity may be the vastest resource to discover compounds with remarkable biological properties. Marine based drug discovery research has been mainly focused on crude extracts. The purpose of this review is to summarize the findings reported in this area, particularly focuses on marine-derived coumarincontaining compounds.