Indole alkaloids from the tunicate Aplidium meridianum

The potential of marine natural Products: Recent Advances in the discovery of Anti-Tuberculosis agents

Tuberculosis (TB) is an infectious airborne disease caused by Mycobacterium tuberculosis. Since the 1990 s, many countries have made significant progress in reducing the incidence of TB and associated mortality by improving health services and strengthening surveillance systems. Nevertheless, due to the emergence of multidrug-resistant TB (MDR-TB), alongside extensively drug-resistant TB (XDR-TB) and TB-HIV co-infection, TB remains one of the lead causes of death arising from infectious disease worldwide, especially in developing countries and disadvantaged populations. Marine natural products (MNPs) have received a large amount of attention in recent years as a source of pharmaceutical constituents and lead compounds, and are expected to offer significant resources and potential in the fields of drug development and biotechnology in the years to come. This review summarizes 169 marine natural products and their synthetic derivatives displaying anti-TB activity from 2013 to the present, including their structures, sources and functions. Partial synthetic information and structure-activity relationships (SARs) are also included.

Investigating the Inhibition of Diindolylmethane Derivatives on SARS-CoV-2 Main Protease

The SARS-CoV-2 main protease (Mpro) is an essential enzyme that promotes viral transcription and replication. Mpro conserved nature in different variants and its nonoverlapping nature with human proteases make it an attractive target for therapeutic intervention against SARS-CoV-2. In this work, the interaction mechanism between Mpro and diindolylmethane derivatives was investigated by molecular docking, enzymatic inhibition assay, UV-vis, fluorescence spectroscopy, and circular dichroism spectroscopy. Results of IC50 values show that 1p (9.87 μM) was the strongest inhibitor for Mpro in this work, which significantly inhibited the activity of Mpro. The binding constant (4.07 × 105 Lmol-1), the quenching constant (5.41 × 105 Lmol-1), and thermodynamic parameters indicated that the quenching mode of 1p was static quenching, and the main driving forces between 1p and Mpro are hydrogen bond and van der Waals force. The influence of molecular structure on the binding is investigated. Chlorine atoms and methoxy groups are favorable for the diindolylmethane derivative inhibitors of Mpro. This work confirms the changes in the microenvironment of Mpro by 1p, and provides clues for the design of potential inhibitors.

Novel meriolin derivatives activate the mitochondrial apoptosis pathway in the presence of antiapoptotic Bcl-2

Meriolin derivatives represent a new class of kinase inhibitors with a pronounced cytotoxic potential. Here, we investigated a newly synthesized meriolin derivative (termed meriolin 16) that displayed a strong apoptotic potential in Jurkat leukemia and Ramos lymphoma cells. Meriolin 16 induced apoptosis in rapid kinetics (within 2-3 h) and more potently (IC50: 50 nM) than the previously described derivatives meriolin 31 and 36 [1]. Exposure of Ramos cells to meriolin 16, 31, or 36 for 5 min was sufficient to trigger severe and irreversible cytotoxicity. Apoptosis induction by all three meriolin derivatives was independent of death receptor signaling but required caspase-9 and Apaf-1 as central mediators of the mitochondrial death pathway. Meriolin-induced mitochondrial toxicity was demonstrated by disruption of the mitochondrial membrane potential (ΔΨm), mitochondrial release of proapoptotic Smac, processing of the dynamin-like GTPase OPA1, and subsequent fragmentation of mitochondria. Remarkably, all meriolin derivatives were able to activate the mitochondrial death pathway in Jurkat cells, even in the presence of the antiapoptotic Bcl-2 protein. In addition, meriolins were capable of inducing cell death in imatinib-resistant K562 and KCL22 chronic myeloid leukemia cells as well as in cisplatin-resistant J82 urothelial carcinoma and 2102EP germ cell tumor cells. Given the frequent inactivation of the mitochondrial apoptosis pathway by tumor cells, such as through overexpression of antiapoptotic Bcl-2, meriolin derivatives emerge as promising therapeutic agents for overcoming treatment resistance.

Natural Bioactive Compounds from Marine Invertebrates That Modulate Key Targets Implicated in the Onset of Type 2 Diabetes Mellitus (T2DM) and Its Complications

BACKGROUND

Type 2 diabetes mellitus (T2DM) is an ongoing, risky, and costly health problem that therefore always requires new treatment options. Moreover, although several drugs are available, only 36% of patients achieve glycaemic control, and patient adherence is a major obstacle. With monotherapy, T2DM and its comorbidities/complications often cannot be managed, and the concurrent administration of several hypoglycaemic drugs is required, which increases the risk of side effects. In fact, despite the efficacy of the drugs currently on the market, they generally come with serious side effects. Therefore, scientific research must always be active in the discovery of new therapeutic agents.

DISCUSSION

The present review highlights some of the recent discoveries regarding marine natural products that can modulate the various targets that have been identified as crucial in the establishment of T2DM disease and its complications, with a focus on the compounds isolated from marine invertebrates. The activities of these metabolites are illustrated and discussed.

OBJECTIVES

The paper aims to capture the relevant evidence of the great chemical diversity of marine natural products as a key tool that can advance understanding in the T2DM research field, as well as in antidiabetic drug discovery. The variety of chemical scaffolds highlighted by the natural hits provides not only a source of chemical probes for the study of specific targets involved in the onset of T2DM, but is also a helpful tool for the development of drugs that are capable of acting via novel mechanisms. Thus, it lays the foundation for the design of multiple ligands that can overcome the drawbacks of polypharmacology.

Progress in the discovery and development of small molecule methuosis inducers

Current cancer chemotherapies rely mainly on the induction of apoptosis of tumor cells, while drug resistance arising from conventional chemicals has always been a big challenge. In recent years, more and more new types of cell deaths including methuosis have been extensively investigated and recognized as potential alternative targets for future cancer treatment. Methuosis is usually caused by excessive accumulation of macropinosomes owing to ectopic activation of macropinocytosis, which can be triggered by external stimuli such as chemical agents. Increasing reports demonstrate that many small molecule compounds could specifically induce methuosis in tumor cells while showing little or no effect on normal cells. This finding raises the possibility of targeting tumor cell methuosis as an effective strategy for the prevention of cancer. Based on fast-growing studies lately, we herein provide a comprehensive overview on the overall research progress of small molecule methuosis inducers. Promisingly, previous efforts and experiences will facilitate the development of next-generation anticancer therapies.

The Synthesis and Biological Evaluation of 2-(1H-Indol-3-yl)quinazolin-4(3H)-One Derivatives

The treatment of many bacterial diseases remains a significant problem due to the increasing antibiotic resistance of their infectious agents. Among others, this is related to Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA) and Mycobacterium tuberculosis. In the present article, we report on antibacterial compounds with activity against both S. aureus and MRSA. A straightforward approach to 2-(1H-indol-3-yl)quinazolin-4(3H)-one and their analogues was developed. Their structural and functional relationships were also considered. The antimicrobial activity of the synthesized compounds against Mycobacterium tuberculosis H₃₇Rv, S. aureus ATCC 25923, MRSA ATCC 43300, Candida albicans ATCC 10231, and their role in the inhibition of the biofilm formation of S. aureus were reported. 2-(5-Iodo-1H-indol-3-yl)quinazolin-4(3H)-one (3k) showed a low minimum inhibitory concentration (MIC) of 0.98 μg/mL against MRSA. The synthesized compounds were assessed via molecular docking for their ability to bind long RSH (RelA/SpoT homolog) proteins using mycobacterial and streptococcal (p)ppGpp synthetase structures as models. The cytotoxic activity of some synthesized compounds was studied. Compounds 3c, f, g, k, r, and 3z displayed significant antiproliferative activities against all the cancer cell lines tested. Indolylquinazolinones 3b, 3e, and 3g showed a preferential suppression of the growth of rapidly dividing A549 cells compared to slower growing fibroblasts of non-tumor etiology.

Geobarrettin D, a Rare Herbipoline-Containing 6-Bromoindole Alkaloid from Geodia barretti

Geobarrettin D (1), a new bromoindole alkaloid, was isolated from the marine sponge Geodia barretti collected from Icelandic waters. Its structure was elucidated by 1D, and 2D NMR (including 1H-15N HSQC, 1H-15N HMBC spectra), as well as HRESIMS data. Geobarrettin D (1) is a new 6-bromoindole featuring an unusual purinium herbipoline moiety. Geobarrettin D (1) decreased secretion of the pro-inflammatory cytokine IL-12p40 by human monocyte derived dendritic cells, without affecting secretion of the anti-inflammatory cytokine IL-10. Thus, compound 1 shows anti-inflammatory activity.

Protecting-Group-Free Synthesis of Meridianin A-G and Derivatives and Its Antibiofilm Evaluation

Herein, a protecting-group-free protocol was developed to realize a time and step economy diversification of the Meridianin alkaloid. A broad range of substituents are tolerated to deliver the products in moderate to high yields, and the first synthesis of Meridianin B was achieved. The simplicity of this protocol enables the rapid construction of a Meridianin derivative library for antibiofilm evaluation. Preliminary results reveal that Meridianin derivatives were capable of inhibiting the Acinetobacter baumannii biofilm and lowering the antibiotic MIC synergistically.

A Survey on the Synthesis of Variolins, Meridianins, and Meriolins-Naturally Occurring Marine (aza)Indole Alkaloids and Their Semisynthetic Derivatives

Marine natural products are a source of essential significance due to a plethora of highly diverse biological properties. The naturally occurring (aza)indole alkaloids variolin B (1), meridianins (2), and their synthetic hybrids meriolins (3) exhibit potent kinase inhibitory activities and have aroused considerable interest in the past two decades. Therefore, the immense demand for versatile synthetic accesses to these structures has considerably increased. This review surveys the synthetic pathways to these naturally occurring alkaloids and their semisynthetic derivatives.

A Review: Meridianins and Meridianins Derivatives

Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been synthesized by drug researchers. This article reviews the extraction and purification methods, biological activities and pharmacological applications, pharmacokinetic characters and chemical synthesis of meridianins and their derivatives. And prospects on discovering new bioactivities of meridianins and optimizing their structure for the improvement of the ADMET properties are provided.

Would Antarctic Marine Benthos Survive Alien Species Invasions? What Chemical Ecology May Tell Us

Many Antarctic marine benthic macroinvertebrates are chemically protected against predation by marine natural products of different types. Antarctic potential predators mostly include sea stars (macropredators) and amphipod crustaceans (micropredators) living in the same areas (sympatric). Recently, alien species (allopatric) have been reported to reach the Antarctic coasts, while deep-water crabs are suggested to be more often present in shallower waters. We decided to investigate the effect of the chemical defenses of 29 representative Antarctic marine benthic macroinvertebrates from seven different phyla against predation by using non-native allopatric generalist predators as a proxy for potential alien species. The Antarctic species tested included 14 Porifera, two Cnidaria, two Annelida, one Nemertea, two Bryozooa, three Echinodermata, and five Chordata (Tunicata). Most of these Antarctic marine benthic macroinvertebrates were chemically protected against an allopatric generalist amphipod but not against an allopatric generalist crab from temperate waters. Therefore, both a possible recolonization of large crabs from deep waters or an invasion of non-native generalist crab species could potentially alter the fundamental nature of these communities forever since chemical defenses would not be effective against them. This, together with the increasing temperatures that elevate the probability of alien species surviving, is a huge threat to Antarctic marine benthos.

Concise Syntheses of Marine (Bis)indole Alkaloids Meridianin C, D, F, and G and Scalaridine A via One-Pot Masuda Borylation-Suzuki Coupling Sequence

N-Protected 3-iodoindoles were reacted with (di)azine halides in a sequentially Pd-catalyzed one-pot fashion, i.e., by Masuda borylation–Suzuki coupling (MBSC) sequence. This methodology was successfully applied to the concise syntheses of marine indole alkaloids meridianin C, D, F, and G, as well as to the bisindole alkaloid scalaridine A, which were obtained in moderate to excellent yield.

Australindolones, New Aminopyrimidine Substituted Indolone Alkaloids from an Antarctic Tunicate Synoicum sp

Five new alkaloids have been isolated from the lipophilic extract of the Antarctic tunicate Synoicum sp. Deep-sea specimens of Synoicum sp. were collected during a 2011 cruise of the R/V Nathanial B. Palmer to the southern Scotia Arc, Antarctica. Crude extracts from the invertebrates obtained during the cruise were screened in a zebrafish-based phenotypic assay. The Synoicum sp. extract induced embryonic dysmorphology characterized by axis truncation, leading to the isolation of aminopyrimidine substituted indolone (1–4) and indole (5–12) alkaloids. While the primary bioactivity tracked with previously reported meridianins A–G (5–11), further investigation resulted in the isolation and characterization of australindolones A–D (1–4) and the previously unreported meridianin H (12).

Design, Synthesis and Structure-Activity Relationship Studies of Meridianin Derivatives as Novel JAK/STAT3 Signaling Inhibitors

Hyperactivation of Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) signaling is an attractive therapeutic target for tumor therapy. Herein, forty-eight novel meridianin derivatives were designed and synthesized, and their antitumor activity was evaluated in vitro both for activity optimization and structure–activity relationship (SAR) study. The results indicated that most derivatives exhibited significantly improved antitumor activity, especially for compound 6e. The compound 6e contains an isothiouronium linked by an alkyl chain consisting of six carbon atoms with IC₅₀ ranging from 1.11 to 2.80 μM on various cancer cell lines. Consistently, the 6e dose dependently induced the apoptosis of A549 and DU145 cells, in which STAT3 is constitutively active. Western blotting assays indicated that the phosphorylation levels of JAK1, JAK2 and STAT3 were inhibited by 6e at 5 μM without significant change in the total STAT3 level. Moreover, 6e also suppressed the expression of STAT3 downstream genes, including c-Myc, Cyclin D1 and Bcl-XL at 10 μM. An additional in vivo study revealed that 6e at the dose of 10 mg/kg could potently inhibit the DU145 xenograft tumor without obvious body weight loss. These results clearly indicate that 6e could be a potential antitumor agent by targeting the JAK/STAT3 signaling pathway.

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Marine Organisms as Alkaloid Biosynthesizers of Potential Anti-Alzheimer Agents

The incidence of neurodegenerative diseases, such as Alzheimer's disease (AD), increases continuously demanding the urgent development of anti-Alzheimer's agents. Marine organisms (MO) have to create their own defenses due to the adverse environment where they live and so synthesize several classes of compounds, such as akaloids, to defend themselves. Therefore, the identification of marine natural products with neuroprotective effects is a necessity. Being that AD is not only a genetic but also an environmental complex disease, a treatment for AD remains to discover. As the major clinical indications (CI) of AD are extracellular plaques formed by β-amyloid (Aβ) protein, intracellular neurofibrillary tangles (NFTs) formed by hyper phosphorylated τ-protein, uncommon inflammatory response and neuron apoptosis and death caused by oxidative stress, alkaloids that may decrease CI, might be used against AD. Most of the alkalolids with those properties are derivatives of the amino acid tryptophan mainly with a planar indole scaffold. Certainly, alkaloids targeting more than one CI, multitarget-directed ligands (MTDL), have the potential to become a lead in AD treatment. Alkaloids to have a maximum of activity against CI, should be planar and contain halogens and amine quaternization.

Ortho-selective C–H arylation of phenols with N-carboxyindoles under Brønsted acid- or Cu(i)-catalysis

Control over chemo- and regioselectivity is a critical issue in the heterobiaryl synthesis via C–H oxidative coupling. To address this challenge, a strategy to invert the normal polarity of indoles in the heterobiaryl coupling was developed. With N-carboxyindoles as umpoled indoles, an exclusively ortho-selective coupling with phenols has been realized, employing a Brønsted acid- or Cu(i)-catalyst (as low as 0.01 mol%). A range of phenols and N-carboxyindoles coupled with exceptional efficiency and selectivity at ambient temperature and the substrates bearing redox-active aryl halides (–Br and –I) smoothly coupled in an orthogonal manner. Notably, preliminary examples of atropselective heterobiaryl coupling have been demonstrated, based on a chiral disulfonimide or a Cu(i)/chiral bisphosphine catalytic system. The reaction was proposed to occur through S_N2′ substitution or a Cu(i)–Cu(iii) cycle, with Brønsted acid or Cu(i) catalysts, respectively.

Control over chemo- and regioselectivity is a critical issue in the heterobiaryl synthesis via C–H oxidative coupling. To address this challenge, a strategy to invert the normal polarity of indoles was developed.

Discovery of an Antarctic Ascidian-Associated Uncultivated Verrucomicrobia with Antimelanoma Palmerolide Biosynthetic Potential

The Antarctic marine ecosystem harbors a wealth of biological and chemical innovation that has risen in concert over millennia since the isolation of the continent and formation of the Antarctic circumpolar current. Scientific inquiry into the novelty of marine natural products produced by Antarctic benthic invertebrates led to the discovery of a bioactive macrolide, palmerolide A, that has specific activity against melanoma and holds considerable promise as an anticancer therapeutic. While this compound was isolated from the Antarctic ascidian Synoicum adareanum, its biosynthesis has since been hypothesized to be microbially mediated, given structural similarities to microbially produced hybrid nonribosomal peptide-polyketide macrolides. Here, we describe a metagenome-enabled investigation aimed at identifying the biosynthetic gene cluster (BGC) and palmerolide A-producing organism. A 74-kbp candidate BGC encoding the multimodular enzymatic machinery (hybrid type I-trans-AT polyketide synthase-nonribosomal peptide synthetase and tailoring functional domains) was identified and found to harbor key features predicted as necessary for palmerolide A biosynthesis. Surveys of ascidian microbiome samples targeting the candidate BGC revealed a high correlation between palmerolide gene targets and a single 16S rRNA gene variant (R = 0.83 to 0.99). Through repeated rounds of metagenome sequencing followed by binning contigs into metagenome-assembled genomes, we were able to retrieve a nearly complete genome (10 contigs) of the BGC-producing organism, a novel verrucomicrobium within the Opitutaceae family that we propose here as “Candidatus Synoicihabitans palmerolidicus.” The refined genome assembly harbors five highly similar BGC copies, along with structural and functional features that shed light on the host-associated nature of this unique bacterium.

IMPORTANCE Palmerolide A has potential as a chemotherapeutic agent to target melanoma. We interrogated the microbiome of the Antarctic ascidian, Synoicum adareanum, using a cultivation-independent high-throughput sequencing and bioinformatic strategy. The metagenome-encoded biosynthetic machinery predicted to produce palmerolide A was found to be associated with the genome of a member of the S. adareanum core microbiome. Phylogenomic analysis suggests the organism represents a new deeply branching genus, “Candidatus Synoicihabitans palmerolidicus,” in the Opitutaceae family of the Verrucomicrobia phylum. The Ca. Synoicihabitans palmerolidicus 4.29-Mb genome encodes a repertoire of carbohydrate-utilizing and transport pathways, a chemotaxis system, flagellar biosynthetic capacity, and other regulatory elements enabling its ascidian-associated lifestyle. The palmerolide producer’s genome also contains five distinct copies of the large palmerolide biosynthetic gene cluster that may provide structural complexity of palmerolide variants.

Marine alkaloids as bioactive agents against protozoal neglected tropical diseases and malaria

Covering: 2000 up to 2021Natural products are an important resource in drug discovery, directly or indirectly delivering numerous small molecules for potential development as human medicines. Among the many classes of natural products, alkaloids have a rich history of therapeutic applications. The extensive chemodiversity of alkaloids found in the marine environment has attracted considerable attention for such uses, while the scarcity of these natural materials has stimulated efforts towards their total synthesis. This review focuses on the biological activity of marine alkaloids (covering 2000 to up to 2021) towards Neglected Tropical Diseases (NTDs) caused by protozoan parasites, and malaria. Chemotherapy represents the only form of treatment for Chagas disease, human African trypanosomiasis, leishmaniasis and malaria, but there is currently a restricted arsenal of drugs, which often elicit severe adverse effects, show variable efficacy or resistance, or are costly. Natural product scaffolds have re-emerged as a focus of academic drug discovery programmes, offering a different resource to discover new chemical entities with new modes of action. In this review, the potential of a range of marine alkaloids is analyzed, accompanied by coverage of synthetic efforts that enable further studies of key antiprotozoal natural product scaffolds.

Evaluation of small molecule kinase inhibitors as novel antimicrobial and antibiofilm agents

Antibiotic resistance is a global and pressing concern. Our current therapeutic arsenal is increasingly limited as bacteria are developing resistance at a rate that far outpaces our ability to create new treatments. Novel approaches to treating and curing bacterial infections are urgently needed. Bacterial kinases have been increasingly explored as novel drug targets and are poised for development into novel therapeutic agents to combat bacterial infections. This review describes several general classes of bacterial kinases that play important roles in bacterial growth, antibiotic resistance, and biofilm formation. General features of these kinase classes are discussed and areas of particular interest for the development of inhibitors will be highlighted. Small molecule kinase inhibitors are described and organized by phenotypic effect, spotlighting particularly interesting inhibitors with novel functions and potential therapeutic benefit. Finally, we provide our perspective on the future of bacterial kinase inhibition as a viable strategy to combat bacterial infections and overcome the pressures of increasing antibiotic resistance.

Ultrasound-assisted synthesis of pyrimidines and their fused derivatives: A review

The pyrimidine scaffold is present in many bioactive drugs; therefore, efficient synthetic routes that provide shorter reaction times, higher yields, and site-selective reactions are constantly being sought. Ultrasound (US) irradiation has emerged as an alternative energy source in the synthesis of these heterocyclic scaffolds, and over the last ten years there has been a significant increase in the number of publications mentioning US in either the construction or derivatization of the pyrimidine core. This review presents a detailed summary (with 140 references) of the effects of US (synergic or not) on the construction and derivatization of the pyrimidine core through classical reactions (e.g., multicomponent, cyclocondensation, cycloaddition, and alkylation reactions). The main points that were taken into consideration are as follows: chemo- and regioselectivity issues, and the results of conventional heating methods compared to US and mechanistic insights that are also presented and discussed for key reactions.

Metabolite Profiling of Meridianin C In Vivo of Rat by UHPLC/Q-TOF MS

Meridianin C (MC), as a marine alkaloid, is a potent protein kinase inhibitor which exhibits good anticancer activity. However, the in vivo metabolism of MC has not been described to date. In this study, an ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF MS) method is employed to investigate the in vivo metabolites of MC in rats. Plasma, bile, urine, and feces are collected after a single oral dose of MC. Protein precipitation, solid phase extraction (SPE), and ultrasonic extraction methods are used to prepare samples. Based on the mass spectral fragmentation patterns, elution order, and retrieving literatures, a total of 13 metabolites of MC were detected and tentatively identified, utilizing MetaboLynx software. The metabolic pathways of MC in rats include N- or O-glucuronidation, O-sulfation, N-hydroxylation, dihydroxylation, and trihydroxylation. The relative content of the metabolites in each kinds of biological samples is also evaluated. This study will help to understand the in vivo properties of MC for the future usage.

Expedient Access to Cyanated N-Heterocycles by Direct Flow-Electrochemical C(sp2 )-H Activation

Nitriles are recurring motifs in bioactive molecules and versatile functional groups in synthetic chemistry. Despite recent progress, direct introduction of a nitrile moiety in heteroarenes remains challenging. Recent developments in electrochemical reactions pave the way to more practical cyanation protocols. However, currently available methods typically require hazardous cyanide sources, expensive mediators, and often suffer from narrow substrate scope and laborious reaction set-up. To address the limitations of current synthetic methods, herein, an effective, sustainable, and scalable procedure for the direct C(sp² )-H cyanation of aromatic N-heterocycles with a user-friendly flow-electrochemical set-up is reported. Furthermore, high substrate and functional-group tolerance is demonstrated, allowing late-stage functionalization of drug-like scaffolds, such as natural products and pharmaceuticals.

Development of New Meridianin/Leucettine-Derived Hybrid Small Molecules as Nanomolar Multi-Kinase Inhibitors with Antitumor Activity

Although the sea ecosystem offers a broad range of bioactivities including anticancer, none of the FDA-approved antiproliferative protein kinase inhibitors are derived from a marine source. In a step to develop new marine-inspired potent kinase inhibitors with antiproliferative activities, a new series of hybrid small molecules (5a–5g) was designed and synthesized based on chemical moieties derived from two marine natural products (Meridianin E and Leucettamine B). Over a panel of 14 cancer-related kinases, a single dose of 10 µM of the parent hybrid 5a possessing the benzo[d][1,3]dioxole moiety of Leucettamine B was able to inhibit the activity of FMS, LCK, LYN, and DAPK1 kinases with 82.5 ± 0.6, 81.4 ± 0.6, 75.2 ± 0.0, and 55 ± 1.1%, respectively. Further optimization revealed the most potent multiple kinase inhibitor of this new series (5g) with IC₅₀ values of 110, 87.7, and 169 nM against FMS, LCK, and LYN kinases, respectively. Compared to imatinib (FDA-approved multiple kinase inhibitor), compound 5g was found to be ~ 9- and 2-fold more potent than imatinib over both FMS and LCK kinases, respectively. In silico docking simulation models of the synthesized compounds within the active site of FMS, LCK, LYN, and DAPK1 kinases offered reasonable explanations of the elicited biological activities. In an in vitro anticancer assay using a library of 60 cancer cell lines that include blood, lung, colon, CNS, skin, ovarian, renal, prostate, and breast cancers, it was found that compound 5g was able to suppress 60 and 70% of tumor growth in leukemia SR and renal RXF 393 cell lines, respectively. Moreover, an ADME study indicated a suitable profile of compound 5g concerning cell permeability and blood-brain barrier (BBB) impermeability, avoiding possible CNS side effects. Accordingly, compound 5g is reported as a potential lead towards novel antiproliferative marine-derived kinase modulators.

GSK-3β, FYN, and DYRK1A: Master Regulators in Neurodegenerative Pathways

Protein kinases (PKs) have been recognized as central nervous system (CNS)-disease-relevant targets due to their master regulatory role in different signal transduction cascades in the neuroscience space. Among them, GSK-3β, FYN, and DYRK1A play a crucial role in the neurodegeneration context, and the deregulation of all three PKs has been linked to different CNS disorders with unmet medical needs, including Alzheimer’s disease (AD), Parkinson’s disease (PD), frontotemporal lobar degeneration (FTLD), and several neuromuscular disorders. The multifactorial nature of these diseases, along with the failure of many advanced CNS clinical trials, and the lengthy approval process of a novel CNS drug have strongly limited the CNS drug discovery. However, in the near-decade from 2010 to 2020, several computer-assisted drug design strategies have been combined with synthetic efforts to develop potent and selective GSK-3β, FYN, and DYRK1A inhibitors as disease-modifying agents. In this review, we described both structural and functional aspects of GSK-3β, FYN, and DYRK1A and their involvement and crosstalk in different CNS pathological signaling pathways. Moreover, we outlined attractive medicinal chemistry approaches including multi-target drug design strategies applied to overcome some limitations of known PKs inhibitors and discover improved modulators with suitable blood–brain barrier (BBB) permeability and drug-like properties.

Bioactive Compounds with Antiglioma Activity from Marine Species

The search for new chemical compounds with antitumor pharmacological activity is a necessary process for creating more effective drugs for each specific malignancy type. This review presents the outcomes of screening studies of natural compounds with high anti-glioma activity. Despite significant advances in cancer therapy, there are still some tumors currently considered completely incurable including brain gliomas. This review covers the main problems of the glioma chemotherapy including drug resistance, side effects of common anti-glioma drugs, and genetic diversity of brain tumors. The main emphasis is made on the characterization of natural compounds isolated from marine organisms because taxonomic diversity of organisms in seawaters significantly exceeds that of terrestrial species. Thus, we should expect greater chemical diversity of marine compounds and greater likelihood of finding effective molecules with antiglioma activity. The review covers at least 15 classes of organic compounds with their chemical formulas provided as well as semi-inhibitory concentrations, mechanisms of action, and pharmacokinetic profiles. In conclusion, the analysis of the taxonomic diversity of marine species containing bioactives with antiglioma activity is performed noting cytotoxicity indicators and to the tumor cells in comparison with similar indicators of antitumor agents approved for clinical use as antiglioblastoma chemotherapeutics.

Natural products as inspiration for the development of bacterial antibiofilm agents

Natural products have historically been a rich source of diverse chemical matter with numerous biological activities, and have played an important role in drug discovery in many areas including infectious disease. Synthetic and medicinal chemistry have been, and continue to be, important tools to realize the potential of natural products as therapeutics and as chemical probes. The formation of biofilms by bacteria in an infection setting is a significant factor in the recalcitrance of many bacterial infections, conferring increased tolerance to many antibiotics and to the host immune response, and as yet there are no approved therapeutics for combatting biofilm-based bacterial infections. Small molecules that interfere with the ability of bacteria to form and maintain biofilms can overcome antibiotic tolerance conferred by the biofilm phenotype, and have the potential to form combination therapies with conventional antibiotics. Many natural products with anti-biofilm activity have been identified from plants, microbes, and marine life, including: elligic acid glycosides, hamamelitannin, carolacton, skyllamycins, promysalin, phenazines, bromoageliferin, flustramine C, meridianin D, and brominated furanones. Total synthesis and medicinal chemistry programs have facilitated structure confirmation, identification of critical structural motifs, better understanding of mechanistic pathways, and the development of more potent, more accessible, or more pharmacologically favorable derivatives of anti-biofilm natural products.

Marine-natural-products for biocides development: first discovery of meridianin alkaloids as antiviral and anti-phytopathogenic-fungus agents

BACKGROUND

Food is an important strategic material related to national economy and people's livelihood. Plant diseases seriously affect crop yield and quality. Marine natural products are an important source for novel drugs discovery. In this work, meridianin alkaloids were selected as the parent structure. A series of meridianin alkaloid analogues were rationally designed, synthesized and evaluated for their antiviral activities and fungicidal activities.

RESULT

These compounds were found to have good antiviral and fungicidal activities for the first time. The structure-activity relationship (SAR) research revealed that introducing bromine atom at the 5-position of indole ring is beneficial to antiviral activity, but introducing methoxy group is not conducive. Introducing bromine atom at the 6-position of indole ring or nitrogen atom at the 7-position of the indole ring resulted in lower antiviral activity. Most of the meridianin derivatives showed higher anti-TMV activities at 500 μg mL^-1 than Ribavirin, especially for compounds 6c, 8a and 10a. All of the compounds also displayed broad spectrum fungicidal activities against 14 kinds of phytopathogenic fungi at 50 μg mL^-1 .

CONCLUSION

Compound 6c with relatively simple structure and excellent antiviral activity, which is similar to that of Ningnanmycin, emerged as novel anti-TMV lead compound. Compound 5d with broad spectrum and high effect fungicidal activity emerged as a new fungicidal lead compound. Current research lays a solid foundation for the application of meridianin alkaloids in crop protection. © 2019 Society of Chemical Industry.

CDK9 as a Valuable Target in Cancer: From Natural Compounds Inhibitors to Current Treatment in Pediatric Soft Tissue Sarcomas

Cyclin-Dependent Kinases (CDKs) are well-known reliable targets for cancer treatment being often deregulated. Among them, since the transcription-associated CDK9 represents the sentry of cell transcriptional homeostasis, it can be a valuable target for managing cancers in which the transcriptional machinery is dysregulated by tumor-driver oncogenes. Here we give an overview of some natural compounds identified as CDK inhibitors with reported activity also against CDK9, that were taken as a model for the development of highly active synthetic anti-CDK9 agents. After, we summarize the data on CDK9 inhibition in a group of rare pediatric solid tumors such as rhabdomyosarcoma, Ewing’s sarcoma, synovial sarcoma and malignant rhabdoid tumors (soft tissue sarcomas), highlighting the more recent results in this field. Finally, we discuss the perspective and challenge of CDK9 modulation in cancer.

Origins and Bioactivities of Natural Compounds Derived from Marine Ascidians and Their Symbionts

Marine ascidians are becoming important drug sources that provide abundant secondary metabolites with novel structures and high bioactivities. As one of the most chemically prolific marine animals, more than 1200 inspirational natural products, such as alkaloids, peptides, and polyketides, with intricate and novel chemical structures have been identified from ascidians. Some of them have been successfully developed as lead compounds or highly efficient drugs. Although numerous compounds that exist in ascidians have been structurally and functionally identified, their origins are not clear. Interestingly, growing evidence has shown that these natural products not only come from ascidians, but they also originate from symbiotic microbes. This review classifies the identified natural products from ascidians and the associated symbionts. Then, we discuss the diversity of ascidian symbiotic microbe communities, which synthesize diverse natural products that are beneficial for the hosts. Identification of the complex interactions between the symbiont and the host is a useful approach to discovering ways that direct the biosynthesis of novel bioactive compounds with pharmaceutical potentials.

Anticancer Indole-Based Chalcones: A Structural and Theoretical Analysis

The crystal structures of five new chalcones derived from N-ethyl-3-acetylindole with different substituents were investigated: (E)-3-(4-bromophenyl)-1-(1-ethyl-1H-indol-3-yl)prop-2-en-1-one (3a); (E)-3-(3-bromophenyl)-1-(1-ethyl-1H-indol-3-yl)prop-2-en-1-one (3b); (E)-1-(1-ethyl-1H-indol-3-yl)-3-(4-methoxyphenyl)prop-2-en-1-one (3c); (E)-1-(1-ethyl-1H-indol-3-yl)-3-mesitylprop-2-en-1-one (3d); and (E)-1-(1-ethyl-1H-indol-3-yl)-3-(furan-2-yl)prop-2-en-1-one (3e). The molecular packing of the studied compounds is controlled mainly by C–H⋅⋅⋅O hydrogen bonds, C–H⋅⋅⋅π interactions, and π···π stacking interactions, which were quantitatively analyzed using Hirshfeld topology analysis. Using density functional theory (DFT) calculations, the order of polarity (3b ˂ 3d ˂ 3e ˂ 3a ˂ 3c) was determined. Several chemical reactivity indices such as the ionization potential (I), electron affinity (A), chemical potential (μ), hardness (η), electrophilicity (ω) and nucleophilicity (N) indices were calculated, and these properties are discussed and compared. In addition, the antiproliferative activity of the five new chalcones was studied.

Novel meriolin derivatives as rapid apoptosis inducers

3-(Hetero)aryl substituted 7-azaindoles possessing multikinase inhibitor activity are readily accessed in a one-pot Masuda borylation-Suzuki coupling sequence. Several promising derivatives were identified as apoptosis inducers and, emphasizing the multikinase inhibition potential, as sphingosine kinase 2 inhibitors. Our measurements provide additional insights into the structure-activity relationship of meriolin derivatives, suggesting derivatives bearing a pyridine moiety with amino groups in 2-position as most active anticancer compounds and thus as highly promising candidates for future in vivo studies.

Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase 1A (DYRK1A) Inhibitors as Potential Therapeutics

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a member of an evolutionarily conserved family of protein kinases that belongs to the CMGC group of kinases. DYRK1A, encoded by a gene located in the human chromosome 21q22.2 region, has attracted attention due to its association with both neuropathological phenotypes and cancer susceptibility in patients with Down syndrome (DS). Inhibition of DYRK1A attenuates cognitive dysfunctions in animal models for both DS and Alzheimer's disease (AD). Furthermore, DYRK1A has been studied as a potential cancer therapeutic target because of its role in the regulation of cell cycle progression by affecting both tumor suppressors and oncogenes. Consequently, selective synthetic inhibitors have been developed to determine the role of DYRK1A in various human diseases. Our perspective includes a comprehensive review of potent and selective DYRK1A inhibitors and their forthcoming therapeutic applications.

Meridianin D Analogues Display Antibiofilm Activity against MRSA and Increase Colistin Efficacy in Gram-Negative Bacteria

In the last 30 years, development of new classes of antibiotics has slowed, increasing the necessity for new options to treat multidrug resistant bacterial infections. Development of antibiotic adjuvants that increase the effectiveness of currently available antibiotics is a promising alternative approach to classical antibiotic development. Reports of the ability of the natural product meridianin D to modulate bacterial behavior have been rare. Herein, we describe the ability of meridianin D to inhibit biofilm formation of methicillin-resistant Staphylococcus aureus (MRSA) and to increase the potency of colistin against colistin-resistant and sensitive Gram-negative bacteria. Analogues were identified that are capable of inhibiting and dispersing MRSA biofilms and lowering the colistin MIC to below the CLSI breakpoint against Acinetobacter baumannii, Klebsiella pneumoniae, and Escherichia coli.

Efficient Synthesis of Five Types of Heterocyclic Compounds via Intramolecular Elimination Using Ultrasound-Static Heating Technique

An experimental technique, ultrasound-static heating, has been developed for the efficient synthesis of heterocyclic compounds. The technique involves ultrasonic irradiation and static heating processes. First, the ultrasonic irradiation process is performed to form an intermediate of the heterocyclic compound under mild conditions and the subsequent static heating process (heating the intermediate under solvent-free conditions without stirring) produces the target heterocyclic compounds via intramolecular elimination.

Natural products: a hope for glioblastoma patients

Glioblastoma (GBM) is one of the most aggressive malignant tumors with an overall dismal survival averaging one year despite multimodality therapeutic interventions including surgery, radiotherapy and concomitant and adjuvant chemotherapy. Few drugs are FDA approved for GBM, and the addition of temozolomide (TMZ) to standard therapy increases the median survival by only 2.5 months. Targeted therapy appeared promising in in vitro monolayer cultures, but disappointed in preclinical and clinical trials, partly due to the poor penetration of drugs through the blood brain barrier (BBB). Cancer stem cells (CSCs) have intrinsic resistance to initial chemoradiation therapy (CRT) and acquire further resistance via deregulation of many signaling pathways. Due to the failure of classical chemotherapies and targeted drugs, research efforts focusing on the use of less toxic agents have increased. Interestingly, multiple natural compounds have shown antitumor and apoptotic effects in TMZ resistant and p53 mutant GBM cell lines and also displayed synergistic effects with TMZ. In this review, we have summarized the current literature on natural products or product analogs used to modulate the BBB permeability, induce cell death, eradicate CSCs and sensitize GBM to CRT.

TfOH-Catalyzed Reaction between 3-Diazoindolin-2-imines and Electron-Rich Arenes: Access to 3-Aryl-2-aminoindoles

TfOH-catalyzed reactions between 3-diazoindolin-2-imines and electron-rich arenes were disclosed. These metal-free reactions furnished 3-aryl-2-aminoindoles in moderate to excellent yields with the tolerance of a broad range of functional groups.

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.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1340 in 429 papers for 2015), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Natural Products Diversity of Marine Ascidians (Tunicates; Ascidiacea) and Successful Drugs in Clinical Development

This present study reviewed the chemical diversity of marine ascidians and their pharmacological applications, challenges and recent developments in marine drug discovery reported during 1994-2014, highlighting the structural activity of compounds produced by these specimens. Till date only 5% of living ascidian species were studied from <3000 species, this study represented from family didemnidae (32%), polyclinidae (22%), styelidae and polycitoridae (11-12%) exhibiting the highest number of promising MNPs. Close to 580 compound structures are here discussed in terms of their occurrence, structural type and reported biological activity. Anti-cancer drugs are the main area of interest in the screening of MNPs from ascidians (64%), followed by anti-malarial (6%) and remaining others. FDA approved ascidian compounds mechanism of action along with other compounds status of clinical trials (phase 1 to phase 3) are discussed here in. This review highlights recent developments in the area of natural products chemistry and biotechnological approaches are emphasized.