Meridianins, a new family of protein kinase inhibitors isolated from the Ascidian Aplidium meridianum

Amaryllidaceae Alkaloids as Potential Glycogen Synthase Kinase-3β Inhibitors

Glycogen synthase kinase-3β (GSK-3β) is a multifunctional serine/threonine protein kinase that was originally identified as an enzyme involved in the control of glycogen metabolism. It plays a key role in diverse physiological processes including metabolism, the cell cycle, and gene expression by regulating a wide variety of well-known substances like glycogen synthase, tau-protein, and β-catenin. Recent studies have identified GSK-3β as a potential therapeutic target in Alzheimer´s disease, bipolar disorder, stroke, more than 15 types of cancer, and diabetes. GSK-3β is one of the most attractive targets for medicinal chemists in the discovery, design, and synthesis of new selective potent inhibitors. In the current study, twenty-eight Amaryllidaceae alkaloids of various structural types were studied for their potency to inhibit GSK-3β. Promising results have been demonstrated by alkaloids of the homolycorine-{9-O-demethylhomolycorine (IC₅₀ = 30.00 ± 0.71 µM), masonine (IC₅₀ = 27.81 ± 0.01 μM)}, and lycorine-types {caranine (IC₅₀ = 30.75 ± 0.04 μM)}.

Synthesis, antitumor activity and CDK1 inhibiton of new thiazole nortopsentin analogues

A new series of thiazole nortopsentin analogues was conveniently synthesized with fair overall yields. The antiproliferative activity of the new derivatives was tested against different human tumor cell lines of the NCI full panel. Four of them showed good antitumor activity with GI₅₀ values from micro to nanomolar level. The mechanism of the antiproliferative effect of these derivatives, was pro-apoptotic, being associated with externalization of plasma membrane phosphatidylserine and DNA fragmentation. The most active and selective of the new thiazoles confined viable cells in G2/M phase and markedly inhibited in vitro CDK1 activity.

Metabolite profiling of ascidian Styela plicata using LC-MS with multivariate statistical analysis and their antitumor activity

To identify the metabolite distribution in ascidian, we have applied an integrated liquid chromatography- tandem mass spectrometry (LC-MS) metabolomics approach to explore and identify patterns in chemical diversity of invasive ascidian Styela plicata. A total of 71 metabolites were reported among these alkaloids, fatty acids and lipids are the most dominant chemical group. Multivariate statistical analysis, principal component analysis (PCA) showed a clear separation according to chemical diversity and taxonomic groups. PCA and partial least square discriminant analysis were applied to discriminate the chemical group of S. plicata crude compounds and classify the compounds with unknown biological activities. In this study, we reported for the first time that a partially purified methanol extract prepared from the ascidian S. plicata and Ascidia mentula possess antitumor activity against four tumor cell lines with different tumor histotype, such as HeLa (cervical carcinoma), HT29 (colon carcinoma), MCF-7 (breast carcinoma) and M14 (melanoma). S. plicata fraction SP-50 showed strong inhibition of cell proliferation and induced apoptosis in HeLa and HT29 cells, thus indicating S. plicata fraction SP-50 a potential lead compound for anticancer therapy. The molecular mechanism of action and chemotherapeutic potential of these ascidian unknown biomolecules need further research.

Personalized Medicine and Resurrected Hopes for the Management of Alzheimer's Disease: A Modular Approach Based on GSK-3β Inhibitors

Alzheimer's disease (AD) is one of the most common neurological disorders with vast reaching worldwide prevalence. Research attempts to decipher what's happening to the human mind have shown that pathogenesis of AD is associated with misfolded protein intermediates displaying tertiary structure conformational changes eventually leading to forming large polymers of unwanted aggregates. The two hallmarks of AD pathological protein aggregates are extraneuronal β-amyloid (Aβ) based senile plaques and intraneuronal neurofibrillary tangles (NFTs). As such, AD is categorized as a protein misfolding neurodegenerative disease (PMND) . Therapeutic interventions interfering with the formation of these protein aggregates have been widely explored as potential pathways for thwarting AD progression. One such tactic is modulating the function of enzymes involved in the metabolic pathways leading to formation of these misfolded protein aggregates. Much evidence has shown that glycogen synthase kinase-3β (GSK-3β) plays a key role in hyperphosphorylation of tau protein leading eventually to its aggregation to form NFTs. Data presented hereby will display a plethora of information as to how to interfere with progression of AD through the route of GSK-3β activity control.

Synthesis of New (E)-2-(1H-Indole-3-ylcarbonyl)-3-heteroaryl-acrylonitriles via Microwave-Assisted Knoevenagel Condensation

Given the broad spectrum of biological uses of heteroaryl-acrylonitrile derivatives, it is necessary to find simple methods to synthesize and diversify this family of compounds. We report a stereoselective synthesis of a series of new (E)-2-(1H-indole-3-ylcarbonyl)-3-heteroaryl-acrylonitriles (3a–3i) obtained from 3-(cyanoacetyl)indole and heteroaryl-aldehydes under microwave-assisted Knoevenagel reaction at 300 W of potency and 100°C. The desired derivatives (3a–3i) were obtained with variable yields (30–94%) and time reactions (8–90 min). All the heteroaryl-acrylonitriles were characterized by physicoanalytical techniques such IR, 1H, 13C NMR, and electrospray mass spectrometry.

Fischer indole synthesis applied to the total synthesis of natural products

In this review, we are trying to underscore the application of FIS in one of the crucial step of indole construction in the total synthesis of biologically active natural products.

Natural and synthetic bioactive inhibitors of glycogen synthase kinase

Glycogen synthase kinase-3 is a multi-functional serine-threonine kinase and is involved in diverse physiological processes, including metabolism, cell cycle, and gene expression by regulating a wide variety of known substrates like glycogen synthase, tau-protein and β-catenin. Aberrant GSK-3 has been involved in diabetes, inflammation, cancer, Alzheimer's and bipolar disorder. In this review, we present an overview of the involvement of GSK-3 in various signalling pathways, resulting in a number of adverse pathologies due to its dysregulation. In addition, a detailed description of the small molecule inhibitors of GSK-3 with different mode of action discovered or specifically developed for GSK-3 has been presented. Furthermore, some clues for the future optimization of these promising molecules to develop specific drugs inhibiting GSK-3, for the treatment of associated disease conditions have also been discussed.

Aplicyanins – brominated natural marine products with superbasic character

By using quantum chemical methods (B3LYP/6-311+G(2df,p)//B3LYP/6-31G(d)), we investigated the structures of aplicyanin A, aplicyanin B, aplicyanin C, aplicyanin D, aplicyanin E, and aplicyanin F along with their protonated structures. The calculated gas phase proton affinities of aplicyanin A, aplicyanin C, and aplicyanin E are around –250 kcal mol−1 and therefore more than 10 kcal mol−1 higher as in typical proton sponges such as 1,8-bis(dimethylamino)naphthalene. The compounds aplicyanin B, aplicyanin D, and aplicyanin F show reduced proton affinities of approximately –240 kcal mol−1 because of the acetyl group being conjugated with the imine N=C moiety. Nucleus-independent chemical shift (NICS) calculations on the same level of theory do not show any peculiarities, and a reasonable correlation between the toxicity of aplicyanins and the gas phase proton affinity is not observed.

DYRK1A, a Dosage-Sensitive Gene Involved in Neurodevelopmental Disorders, Is a Target for Drug Development in Down Syndrome

Down syndrome (DS) is one of the leading causes of intellectual disability, and patients with DS face various health issues, including learning and memory deficits, congenital heart disease, Alzheimer's disease (AD), leukemia, and cancer, leading to huge medical and social costs. Remarkable advances on DS research have been made in improving cognitive function in mouse models for future therapeutic approaches in patients. Among the different approaches, DYRK1A inhibitors have emerged as promising therapeutics to reduce DS cognitive deficits. DYRK1A is a dual-specificity kinase that is overexpressed in DS and plays a key role in neurogenesis, outgrowth of axons and dendrites, neuronal trafficking and aging. Its pivotal role in the DS phenotype makes it a prime target for the development of therapeutics. Recently, disruption of DYRK1A has been found in Autosomal Dominant Mental Retardation 7 (MRD7), resulting in severe mental deficiency. Recent advances in the development of kinase inhibitors are expected, in the near future, to remove DS from the list of incurable diseases, providing certain conditions such as drug dosage and correct timing for the optimum long-term treatment. In addition the exact molecular and cellular mechanisms that are targeted by the inhibition of DYRK1A are still to be discovered.

Cyclin Dependent Kinase 9 Inhibitors for Cancer Therapy

Cyclin dependent kinase (CDK) inhibitors have been the topic of intense research for nearly 2 decades due to their widely varied and critical functions within the cell. Recently CDK9 has emerged as a druggable target for the development of cancer therapeutics. CDK9 plays a crucial role in transcription regulation; specifically, CDK9 mediated transcriptional regulation of short-lived antiapoptotic proteins is critical for the survival of transformed cells. Focused chemical libraries based on a plethora of scaffolds have resulted in mixed success with regard to the development of selective CDK9 inhibitors. Here we review the regulation of CDK9, its cellular functions, and common core structures used to target CDK9, along with their selectivity profile and efficacy in vitro and in vivo.

Microwave-Assisted Synthesis of Bioactive Six-Membered Heterocycles and Their Fused Analogues

This review describes the formation of six-membered heterocyclic compounds and their fused analogues under microwave activation using modern organic transformations including cyclocondensation, cycloaddition, multicomponents and other modular reactions. The review is divided according to the main heterocycle types in order of increasing complexity, starting with heterocyclic systems containing one, two and three heteroatoms and their fused analogues. Recent microwave applications are reviewed, with special focus on the chemistry of bioactive compounds. Selected examples from the 2006 to 2015 literature are discussed.

DYRK1A inhibition as potential treatment for Alzheimer's disease

In total, 47,500,000 people worldwide are affected by dementia and this number is estimated to double by 2030 and triple within 2050 resulting in a huge burden on public health. Alzheimer's disease (AD), a progressive neurodegenerative disorder, is the most common cause of dementia, accounting for 60-70% of all the cases. The cause of AD is still poorly understood but several brain abnormalities (e.g., loss of neuronal connections and neuronal death) have been identified in affected patients. In addition to the accumulation of β-amyloid plaques in the brain tissue, aberrant phosphorylation of tau proteins has proved to increase neuronal death. DYRK1A phosphorylates tau on 11 different Ser/Thr residues, resulting in the formation of aggregates called 'neurofibrillary tangles' which, together with amyloid plaques, could be responsible for dementia, neuronal degeneration and cell death. Small molecule inhibition of DYRK1A could thus represent an interesting approach toward the treatment of Alzheimer's and other neurodegenerative diseases. Herein we review the current progress in the identification and development of DYRK1A inhibitors.

Docking and ADMET prediction of few GSK-3 inhibitors divulges 6-bromoindirubin-3-oxime as a potential inhibitor

GSK-3 is a member of cellular kinases with diversified functions such as cellular differentiation, metabolic signaling, neuronal functions and apoptosis. It has been validated as an important therapeutic target in Alzheimer's disease and type 2 diabetes. Few molecules targeting GSK-3 are currently in clinical trials. In this study, we have compared certain docking and computational ADME (Absorption, Distribution, Metabolism, Excretion) parameters of a few GSK-3 targeted ligands (Indirubin, Hymenialdisine, Meridianins, 6-bromoindirubin-3-oxime) against two control molecules (Tideglusib and LY-2090314) to derive and analyze the basic drug-like properties of the test compounds. Docking between the GSK-3 and various ligands was done using AutoDock while ADME parameters were derived from ADMET server PreADMET and admetSAR. Various docked images were retrieved from docking, indicating the docking sites in the target protein. Out of four compounds tested, 6-bromoindirubin-3-oxime (6-BIO) was found as the best docking and ADME parameters, followed by Hymenialdisine (HMD). The LigPlot interaction results show two residues Leu (188) and Thr (138) to be common at the interaction site. The LD50 of 6-BIO is better than one of the control ligands while very similar to the other. Some of the parameters were very similar to the control ligands, thus, making it a suitable candidate among the test ligands. From this in-silico study, we concluded that 6-BIO is a potent drug candidate which could be further tested in vitro and in vivo to establish a drug molecule. Since, 6-BIO is a chemically modified form of the basic molecule Indirubin, we can hypothesize that certain other modified indirubins could be tested as GSK-3 targeted ligands.

Meridianin derivatives as potent Dyrk1A inhibitors and neuroprotective agents

Meridianins are a group of marine-derived indole alkaloids which are reported to possess kinase inhibitory activities. In the present Letter, we report synthesis of N1-substituted and C-ring modified meridianin derivatives and their evaluation as Dyrk1A inhibitors and neuroprotective agents. Among the library of 52 compounds screened, morpholinoyl linked derivative 26b and 2-nitro-4-trifluoromethyl phenyl sulfonyl derivative 29v displayed potent inhibition of Dyrk1A with IC50 values of 0.5 and 0.53 μM, respectively. The derivative 26b also inhibited Dyrk2 and Dyrk3 with IC50 values of 1.4 and 2.2 μM, respectively showing 2.2 and 4.4 fold selectivity for Dyrk1A with respect to Dyrk2 and Dyrk3. The compound 26b was not cytotoxic to human neuroblastoma SH-SY5Y cells (IC50>100 μM) and it displayed significant neuroprotection against glutamate-induced neurotoxicity in these cells at 10 μM. Molecular modelling studies of compound 26b led to identification of key interactions in the binding site of Dyrk1A and the possible reasons for observed Dyrk1A selectivity over Dyrk2.

Luciferin and derivatives as a DYRK selective scaffold for the design of protein kinase inhibitors

D-Luciferin is widely used as a substrate in luciferase catalysed bioluminescence assays for in vitro studies. However, little is known about cross reactivity and potential interference of D-luciferin with other enzymes. We serendipitously found that firefly luciferin inhibited the CDK2/Cyclin A protein kinase. Inhibition profiling of D-luciferin over a 103-protein kinase panel showed significant inhibition of a small set of protein kinases, in particular the DYRK-family, but also other members of the CMGC-group, including ERK8 and CK2. Inhibition profiling on a 16-member focused library derived from D-luciferin confirms that D-luciferin represents a DYRK-selective chemotype of fragment-like molecular weight. Thus, observation of its inhibitory activity and the initial SAR information reported here promise to be useful for further design of protein kinase inhibitors with related scaffolds.

Targeting cyclin-dependent kinases in human cancers: from small molecules to Peptide inhibitors

Cyclin-dependent kinases (CDK/Cyclins) form a family of heterodimeric kinases that play central roles in regulation of cell cycle progression, transcription and other major biological processes including neuronal differentiation and metabolism. Constitutive or deregulated hyperactivity of these kinases due to amplification, overexpression or mutation of cyclins or CDK, contributes to proliferation of cancer cells, and aberrant activity of these kinases has been reported in a wide variety of human cancers. These kinases therefore constitute biomarkers of proliferation and attractive pharmacological targets for development of anticancer therapeutics. The structural features of several of these kinases have been elucidated and their molecular mechanisms of regulation characterized in depth, providing clues for development of drugs and inhibitors to disrupt their function. However, like most other kinases, they constitute a challenging class of therapeutic targets due to their highly conserved structural features and ATP-binding pocket. Notwithstanding, several classes of inhibitors have been discovered from natural sources, and small molecule derivatives have been synthesized through rational, structure-guided approaches or identified in high throughput screens. The larger part of these inhibitors target ATP pockets, but a growing number of peptides targeting protein/protein interfaces are being proposed, and a small number of compounds targeting allosteric sites have been reported.

Alkaloids from marine invertebrates as important leads for anticancer drugs discovery and development

The present review describes research on novel natural antitumor alkaloids isolated from marine invertebrates. The structure, origin, and confirmed cytotoxic activity of more than 130 novel alkaloids belonging to several structural families (indoles, pyrroles, pyrazines, quinolines, and pyridoacridines), together with some of their synthetic analogs, are illustrated. Recent discoveries concerning the current state of the potential and/or development of some of them as new drugs, as well as the current knowledge regarding their modes of action, are also summarized. A special emphasis is given to the role of marine invertebrate alkaloids as an important source of leads for anticancer drug discovery.

Discovery of thienoquinolone derivatives as selective and ATP non-competitive CDK5/p25 inhibitors by structure-based virtual screening

Calpain mediated cleavage of CDK5 natural precursor p35 causes a stable complex formation of CDK5/p25, which leads to hyperphosphorylation of tau. Thus inhibition of this complex is a viable target for numerous acute and chronic neurodegenerative diseases involving tau protein, including Alzheimer's disease. Since CDK5 has the highest sequence homology with its mitotic counterpart CDK2, our primary goal was to design selective CDK5/p25 inhibitors targeting neurodegeneration. A novel structure-based virtual screening protocol comprised of e-pharmacophore models and virtual screening workflow was used to identify nine compounds from a commercial database containing 2.84 million compounds. An ATP non-competitive and selective thieno[3,2-c]quinolin-4(5H)-one inhibitor (10) with ligand efficiency (LE) of 0.3 was identified as the lead molecule. Further SAR optimization led to the discovery of several low micromolar inhibitors with good selectivity. The research represents a new class of potent ATP non-competitive CDK5/p25 inhibitors with good CDK2/E selectivity.

Natural products from marine organisms with neuroprotective activity in the experimental models of Alzheimer's disease, Parkinson's disease and ischemic brain stroke: their molecular targets and action mechanisms

Continuous increases in the incidence of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), and brain stroke demand the urgent development of therapeutics. Marine organisms are well-known producers of natural products with diverse structures and pharmacological activities. Therefore, researchers have endeavored to identify marine natural products with neuroprotective effects. In this regard, this review summarizes therapeutic targets for AD, PD, and ischemic brain stroke and marine natural products with pharmacological activities on the targets according to taxonomies of marine organisms. Furthermore, several marine natural products on the clinical trials for the treatment of neurological disorders are discussed.

Defensive metabolites from Antarctic invertebrates: does energetic content interfere with feeding repellence?

Many bioactive products from benthic invertebrates mediating ecological interactions have proved to reduce predation, but their mechanisms of action, and their molecular identities, are usually unknown. It was suggested, yet scarcely investigated, that nutritional quality interferes with defensive metabolites. This means that antifeedants would be less effective when combined with energetically rich prey, and that higher amounts of defensive compounds would be needed for predator avoidance. We evaluated the effects of five types of repellents obtained from Antarctic invertebrates, in combination with diets of different energetic values. The compounds came from soft corals, ascidians and hexactinellid sponges; they included wax esters, alkaloids, a meroterpenoid, a steroid, and the recently described organic acid, glassponsine. Feeding repellency was tested through preference assays by preparing diets (alginate pearls) combining different energetic content and inorganic material. Experimental diets contained various concentrations of each repellent product, and were offered along with control compound-free pearls, to the Antarctic omnivore amphipod Cheirimedon femoratus. Meridianin alkaloids were the most active repellents, and wax esters were the least active when combined with foods of distinct energetic content. Our data show that levels of repellency vary for each compound, and that they perform differently when mixed with distinct assay foods. The natural products that interacted the most with energetic content were those occurring in nature at higher concentrations. The bioactivity of the remaining metabolites tested was found to depend on a threshold concentration, enough to elicit feeding repellence, independently from nutritional quality.

Impact of meriolins, a new class of cyclin-dependent kinase inhibitors, on malignant glioma proliferation and neo-angiogenesis

BACKGROUND

Glioblastomas are the most frequent and most aggressive primary brain tumors in adults. The median overall survival is limited to a few months despite surgery, radiotherapy, and chemotherapy. It is now clearly established that hyperactivity of cyclin-dependent kinases (CDKs) is one of the processes underlying hyperproliferation and tumoral growth. The marine natural products meridianins and variolins, characterized as CDK inhibitors, display a kinase-inhibitory activity associated with cytotoxic effects. In order to improve selectivity and efficiency of these CDK inhibitors, a series of hybrid compounds called meriolins have been synthesized.

METHODS

The potential antitumoral activity of meriolins was investigated in vitro on glioma cell lines (SW1088 and U87), native neural cells, and a human endothelial cell line (HUV-EC-C). The impact of intraperitoneal or intratumoral administrations of meriolin 15 was evaluated in vivo on 2 different nude mice-xenografted glioma models.

RESULTS

Meriolins 3, 5, and 15 exhibited antiproliferative properties with nanomolar IC50 and induced cell-cycle arrest and CDK inhibition associated with apoptotic events in human glioma cell lines. These meriolins blocked the proliferation rate of HUV-EC-C through cell cycle arrest and apoptosis. In vivo, meriolin 15 provoked a robust reduction in tumor volume in spite of toxicity for highest doses, associated with inhibition of cell division, activation of caspase 3, reduction of CD133 cells, and modifications of the vascular architecture.

CONCLUSION

Meriolins, and meriolin 15 in particular, exhibit antiproliferative and proapoptotic activities on both glioma and intratumoral endothelial cells, constituting key promising therapeutic lead compounds for the treatment of glioblastoma.

Bioactive marine drugs and marine biomaterials for brain diseases

Marine invertebrates produce a plethora of bioactive compounds, which serve as inspiration for marine biotechnology, particularly in drug discovery programs and biomaterials development. This review aims to summarize the potential of drugs derived from marine invertebrates in the field of neuroscience. Therefore, some examples of neuroprotective drugs and neurotoxins will be discussed. Their role in neuroscience research and development of new therapies targeting the central nervous system will be addressed, with particular focus on neuroinflammation and neurodegeneration. In addition, the neuronal growth promoted by marine drugs, as well as the recent advances in neural tissue engineering, will be highlighted.

Pim kinase inhibitory and antiproliferative activity of a novel series of meridianin C derivatives

A novel series of meridianin C derivatives substituted at C-5 position were prepared. These derivatives were tested for their kinase inhibitory potencies against all three family members of the pim kinases (Pim-1, Pim-2 and Pim-3). In addition, their antiproliferative activity towards three human leukemia cell lines as MV4-11, Jurkat clone E6-1 and K562 has been evaluated. Structure activity relationships at C-3 and C-5 positions of indole were performed to better understand the mechanism behind the enhanced potency. Compound 7f, the most active compound of the series showed a single-digit nanomolar IC50 with selectivity towards Pim-1 kinase.

Concise syntheses of meridianins and meriolins using a catalytic domino amino-palladation reaction

A synthesis of natural and synthetic members of the meridianin family of kinase inhibitory natural products has been developed. The sequence utilizes a variation of the Cacchi palladium-catalyzed domino reaction to efficiently construct the heterocyclic framework of the meridianins and meriolins from monocyclic precursors.

Recent progress in neuroactive marine natural products

This review covers the isolation, chemical structure, biological activity, structure activity relationships including synthesis of chemical probes, and pharmacological characterization of neuroactive marine natural products; 302 references are cited.

Catalyst-free tandem Michael addition/decarboxylation of (thio)coumarin-3-carboxylic acids with indoles: facile synthesis of indole-3-substituted 3,4-dihydro(thio)coumarins

The tandem Michael addition/decarboxylation of (thio)-coumarin-3-carboxylic acids with indoles gives biologically important indole-3-substituted dihydrocoumarins in good to excellent yields under catalyst-free conditions.

Structure- and ligand-based drug design of novel p38-alpha MAPK inhibitors in the fight against the Alzheimer's disease

Alzheimer's disease (AD) is characterized microscopically by the presence of amyloid plaques, which are accumulations of beta-amyloid protein inter-neurons, and neurofibrillary tangles formed predominantly by highly phosphorylated forms of the microtubule-associated protein, tau, which form tangled masses that consume neuronal cell body, possibly leading to neuronal dysfunction and ultimately death. p38α mitogen-activated protein kinase (MAPK) has been implicated in both events associated with AD, tau phosphorylation and inflammation. p38α MAPK pathway is activated by a dual phosphorylation at Thr180 and Tyr182 residues. Drug design of p38α MAPK inhibitors is mainly focused on small molecules that compete for Adenosine triphosphate in the catalytic site. Here, we used different approaches of structure- and ligand-based drug design and medicinal chemistry strategies based on a selected p38α MAPK structure deposited in the Protein Data Bank in complex with inhibitor, as well as others reported in literature. As a result of the virtual screening experiments performed here, as well as molecular dynamics, molecular interaction fields studies, shape and electrostatic similarities, activity and toxicity predictions, and pharmacokinetic and physicochemical properties, we have selected 13 compounds that meet the criteria of low or no toxicity potential, good pharmacotherapeutic profile, predicted activities, and calculated values ​​comparable with those obtained for the reference compounds, while maintaining the main interactions observed for the most potent inhibitors.

Engineering of indole-based tethered biheterocyclic alkaloid meridianin into β-carboline-derived tetracyclic polyheterocycles via amino functionalization/6-endo cationic π-cyclization

A mild, efficient and versatile method has been developed for the construction of a functionalized natural product, meridianin, and its post conversion to pyrimido-β-carboline by cationic π- cyclization. The strategy involves the introduction of an amino group at the C-5 of the pyrimidine ring and utilizing the nucleophilictiy of the C-2 in the indole ring to facilitate cationic π-cyclization.

Natural products from Antarctic colonial ascidians of the genera Aplidium and Synoicum: variability and defensive role

Ascidians have developed multiple defensive strategies mostly related to physical, nutritional or chemical properties of the tunic. One of such is chemical defense based on secondary metabolites. We analyzed a series of colonial Antarctic ascidians from deep-water collections belonging to the genera Aplidium and Synoicum to evaluate the incidence of organic deterrents and their variability. The ether fractions from 15 samples including specimens of the species A. falklandicum, A. fuegiense, A. meridianum, A. millari and S. adareanum were subjected to feeding assays towards two relevant sympatric predators: the starfish Odontaster validus, and the amphipod Cheirimedon femoratus. All samples revealed repellency. Nonetheless, some colonies concentrated defensive chemicals in internal body-regions rather than in the tunic. Four ascidian-derived meroterpenoids, rossinones B and the three derivatives 2,3-epoxy-rossinone B, 3-epi-rossinone B, 5,6-epoxy-rossinone B, and the indole alkaloids meridianins A–G, along with other minoritary meridianin compounds were isolated from several samples. Some purified metabolites were tested in feeding assays exhibiting potent unpalatabilities, thus revealing their role in predation avoidance. Ascidian extracts and purified compound-fractions were further assessed in antibacterial tests against a marine Antarctic bacterium. Only the meridianins showed inhibition activity, demonstrating a multifunctional defensive role. According to their occurrence in nature and within our colonial specimens, the possible origin of both types of metabolites is discussed.

Small-Molecule Inhibitors of GSK-3: Structural Insights and Their Application to Alzheimer's Disease Models

The world health organization (WHO) estimated that 18 million people are struck by Alzheimer's disease (AD). The USA, France, Germany, and other countries launched major programmes targeting the identification of risk factors, the improvement of caretaking, and fundamental research aiming to postpone the onset of AD. The glycogen synthase kinase 3 (GSK-3) is implicated in multiple cellular processes and has been linked to the pathogenesis of several diseases including diabetes mellitus, cancer, and AD. Inhibition of GSK-3 leads to neuroprotective effects, decreased β-amyloid production, and a reduction in tau hyperphosphorylation, which are all associated with AD. Various classes of small molecule GSK-3 inhibitors have been published in patents and original publications. Herein, we present a comprehensive summary of small molecules reported to interact with GSK-3. We illustrate the interactions of the inhibitors with the active site. Furthermore, we refer to the biological characterisation in terms of activity and selectivity for GSK-3, elucidate in vivo studies and pre-/clinical trials.