Ecteinascidins 729, 743, 745, 759A, 759B, and 770: potent antitumor agents from the Caribbean tunicate Ecteinascidia turbinata

Development of Cyclic N,O-Aminal-Embedded Bis-tetrahydroisoquinoline Analogues as Potential DNA Alkylation Agents

This work described a novel "functional hybrid" design for bis-tetrahydroisoquinoline (bis-THIQ) analogues as potential DNA alkylation agents by replacing the labile C21-carbinolamine on the bis-THIQ skeleton of ET-743 with a chemically stable cyclic N,O-aminal functionality. In vitro anti-proliferation evaluation has proven that it is a successful approach to deliver new bis-THIQ analogues with common cytotoxicities, among which several exhibited sub-micromolar-range IC50 against the proliferation of human cancer cell lines A549, HepG2, and MDA-MB-231, respectively.

Marine-Derived Anticancer Agents Targeting Apoptotic Pathways: Exploring the Depths for Novel Cancer Therapies

Extensive research has been conducted on the isolation and study of bioactive compounds derived from marine sources. Several natural products have demonstrated potential as inducers of apoptosis and are currently under investigation in clinical trials. These marine-derived compounds selectively interact with extrinsic and intrinsic apoptotic pathways using a variety of molecular mechanisms, resulting in cell shrinkage, chromatin condensation, cytoplasmic blebs, apoptotic bodies, and phagocytosis by adjacent parenchymal cells, neoplastic cells, or macrophages. Numerous marine-derived compounds are currently undergoing rigorous examination for their potential application in cancer therapy. This review examines a total of 21 marine-derived compounds, along with their synthetic derivatives, sourced from marine organisms such as sponges, corals, tunicates, mollusks, ascidians, algae, cyanobacteria, fungi, and actinobacteria. These compounds are currently undergoing preclinical and clinical trials to evaluate their potential as apoptosis inducers for the treatment of different types of cancer. This review further examined the compound's properties and mode of action, preclinical investigations, clinical trial studies on single or combination therapy, and the prospective development of marine-derived anticancer therapies.

An organic extract from ascidian Ciona robusta induces cytotoxic autophagy in human malignant cell lines

The last decades have seen an increase in the isolation and characterization of anticancer compounds derived from marine organisms, especially invertebrates, and their use in clinical trials. In this regard, ascidians, which are included in the subphylum Tunicata, represent successful examples with two drugs, Aplidine© and Yondelis© that reached the market as orphan drugs against several malignancies. Here, we report that an organic extract prepared from homogenized tissues of the Mediterranean ascidian Ciona robusta inhibited cell proliferation in HT-29, HepG2, and U2OS human cells with the former being the most sensitive to the extract (EC50 = 250 μg/mL). We demonstrated that the ascidian organic extract was not cytotoxic on HT-29 cells that were induced to differentiate with sodium butyrate, suggesting a preference for the mixture for the malignant phenotype. Finally, we report that cell death induced by the organic extract was mediated by the activation of a process of cytotoxic autophagy as a result of the increased expression of the LC3-II marker and number of autophagic vacuoles, which almost doubled in the treated HT-29 cells. In summary, although the detailed chemical composition of the Ciona robusta extract is still undetermined, our data suggest the presence of bioactive compounds possessing anticancer activity.

The potential of marine-derived piperazine alkaloids: Sources, structures and bioactivities

Marine-derived piperazine alkaloids (MDPAs) constitute a significant group of natural compounds known for their diverse structures and biological activities. Over the past five decades, substantial efforts have been devoted to isolating these alkaloids from marine sources and characterizing their chemical and bioactive profiles. To date, a total of 922 marine-derived piperazine alkaloids have been reported from various marine organisms. These compounds demonstrate a wide range of pharmacological properties, including cytotoxicity, antibacterial, antifungal, antiviral, and various other activities. Notably, among these activities, cytotoxicity emerges as the most prominent characteristic of marine-derived piperazine alkaloids. This review also summarizes the structure-activity relationship (SAR) studies associated with the cytotoxicity of these compounds. In summary, our objective is to provide an overview of the research progress concerning marine-derived piperazine alkaloids, with the aim of fostering their continued development and utilization.

Recent advances in the synthesis and activity of analogues of bistetrahydroisoquinoline alkaloids as antitumor agents

Ecteinascidin 743 (Et-743), also known by the trade name Yondelis®, is the pioneering marine natural product to be successfully developed as an antitumor drug. Moreover, it is the first tetrahydroisoquinoline natural product used clinically for antitumor therapy since Kluepfel, a Canadian scientist, discovered the tetrahydroisoquinoline alkaloid (THIQ) naphthyridinomycin in 1974. Currently, almost a hundred natural products of bistetrahydroisoquinoline type have been reported. Majority of these bistetrahydroisoquinoline alkaloids exhibit diverse pharmacological activities, with some family members portraying potent antitumor activities such as Ecteinascidins, Renieramycins, Saframycins, Jorumycins, among others. Due to the unique chemical structure and exceptional biological activity of these natural alkaloids, coupled with their scarcity in nature, research seeking to provide material basis for further bioactivity research through total synthesis and obtaining compound leads with medicinal value through structural modification, remains a hot topic in the field of antitumor drug R&D. Despite the numerous reviews on the total synthesis of bistetrahydroisoquinoline natural products, comprehensive reviews on their structural modification are apparently scarce. Moreover, structural modification of bioactive natural products to acquire lead compounds with improved pharmaceutical characteristics, is a crucial approach for innovative drug discovery. This paper presents an up-to-date review of both structural modification and activity of bistetrahydroisoquinoline natural products. It highlights how such alkaloids can be used as antitumor lead compounds through careful chemical modifications. This review offers valuable scientific references for pharmaceutical chemists engaged in developing novel antitumor agents based on such alkaloid modifications, as well as those with such a goal in future.

Isochromenylium/Isoquinolinium-Mediated One-Pot Annulation to Hexahydropyrazinoisoquinolines. Synthesis of Quinocarcinol

A novel annulation protocol has been successfully developed in this work for the quick generation of 1,3,4,6,11,11a-hexahydro-2H-pyrazino[1,2-b]isoquinolines from easily accessible o-alkynylbenzaldehydes. Various hexahydropyrazinoisoquinolines, including those previously unavailable with electron-deficient substituents, have been achieved via the newly developed continuously operational isochromenylium/isoquinolinium-mediated procedure. It also perfectly served as a key step to generate the basic skeleton in the new total synthesis of quinocarcinol, accompanied by the development and application of a direct late-stage stereoselective sp3 C-H hydroxymethylation.

Formal Synthesis of Ecteinascidin 743 from N-Cbz-l-tyrosine

A formal total synthesis of ecteinascidin 743 and lurbinectedin is achieved. Key features involve a Pictet-Spengler cyclization coupling of the tetrahydroisoquinoline and phenylalaninol moieties prepared by a common route with high yield and selectivity, a Parikh-Doering oxidation with good chemoselectivity and functionality tolerance, and a light-mediated A-ring elaboration of pentacyclic methoxyquinone substrates. By the approach, the known advanced intermediate (4-step conversion to Et-743) can be obtained conveniently in 21 total steps from N-Cbz-l-tyrosine.

Sulfur-containing marine natural products as leads for drug discovery and development

Among the large series of marine natural products (MNPs), sulfur-containing MNPs have emerged as potential therapeutic agents for the treatment of a range of diseases. Herein, we reviewed 95 new sulfur-containing MNPs isolated during the period between 2021 and March 2023. In addition, we discuss that the widely used strategies and the emerging technologies including natural product-based antibody drug conjugates (ADCs), small-molecule-based proteolysis targeting chimeras (PROTACs), nanotechnology-based drug carriers, artificial intelligence (AI)-driven drug discovery have been used for improving the efficiency and success rate of NP-based drug development. We also provide perspectives regarding the challenges and opportunities in sulfur-containing MNPs based drug discovery and development and future research directions.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp³-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Formal Synthesis of Ecteinascidin 743 via an Intramolecular Cascade Heck Reaction to Construct the Diazabicyclo[3.3.1]nonane Framework

A synthetic route to ecteinascidin 743 has been established via an intramolecular cascade Heck reaction to construct the diazabicyclo[3.3.1]nonane skeleton while controlling the two contiguous stereogenic centers. The strategically formed five-membered ring was oxidatively cleaved to generate a dialdehyde intermediate, from which the B ring of ecteinascidin 743 was constructed.

Marine Compounds for Melanoma Treatment and Prevention

Melanoma is considered a multifactorial disease etiologically divided into melanomas related to sun exposure and those that are not, but also based on their mutational signatures, anatomic site, and epidemiology. The incidence of melanoma skin cancer has been increasing over the past decades with 132,000 cases occurring globally each year. Marine organisms have been shown to be an excellent source of natural compounds with possible bioactivities for human health applications. In this review, we report marine compounds from micro- and macro-organisms with activities in vitro and in vivo against melanoma, including the compound Marizomib, isolated from a marine bacterium, currently in phase III clinical trials for melanoma. When available, we also report active concentrations, cellular targets and mechanisms of action of the mentioned molecules. In addition, compounds used for UV protection and melanoma prevention from marine sources are discussed. This paper gives an overview of promising marine molecules which can be studied more deeply before clinical trials in the near future.

Antitumor Potential of Immunomodulatory Natural Products

Cancer is one of the leading causes of death globally. Anticancer drugs aim to block tumor growth by killing cancerous cells in order to prevent tumor progression and metastasis. Efficient anticancer drugs should also minimize general toxicity towards organs and healthy cells. Tumor growth can also be successfully restrained by targeting and modulating immune response. Cancer immunotherapy is assuming a growing relevance in the fight against cancer and has recently aroused much interest for its wider safety and the capability to complement conventional chemotherapeutic approaches. Natural products are a traditional source of molecules with relevant potential in the pharmacological field. The huge structural diversity of metabolites with low molecular weight (small molecules) from terrestrial and marine organisms has provided lead compounds for the discovery of many modern anticancer drugs. Many natural products combine chemo-protective and immunomodulant activity, thus offering the potential to be used alone or in association with conventional cancer therapy. In this review, we report the natural products known to possess antitumor properties by interaction with immune system, as well as discuss the possible immunomodulatory mechanisms of these molecules.

Biosynthesis of Piperazine-Derived Diazabicyclic Alkaloids Involves a Nonribosomal Peptide Synthetase and Subsequent Tailoring by a Multifunctional Cytochrome P450 Enzyme

Piperazine-derived diazabicycles are privileged structures found in natural products and synthetic chemical entities, including therapeutic agents. Herein, we deciphered the biosynthesis of two unique classes of diazabicyclic alkaloids, fischerazines A-C. Notably, we characterized a multifunctional P450 monooxygenase NfiC that installs ortho-dihydroxyl groups on the dibenzyl-piperazines, in turn triggering a range of NfiC-catalyzed and spontaneous cyclization events.

Impact of Co-Culture on the Metabolism of Marine Microorganisms

Natural products from plants have been listed for hundreds of years as a source of biologically active molecules. In recent years, the marine environment has demonstrated its ability to provide new structural entities. More than 70% of our planet’s surface is covered by oceans, and with the technical advances in diving and remotely operated vehicles, it is becoming easier to collect samples. Although the risk of rediscovery is significant, the discovery of silent gene clusters and innovative analytical techniques has renewed interest in natural product research. Different strategies have been proposed to activate these silent genes, including co-culture, or mixed fermentation, a cultivation-based approach. This review highlights the potential of co-culture of marine microorganisms to induce the production of new metabolites as well as to increase the yields of respective target metabolites with pharmacological potential, and moreover to indirectly improve the biological activity of a crude extract.

Characterization of the nucleotide excision repair pathway and evaluation of compounds for overcoming the cisplatin resistance of non‑small cell lung cancer cell lines

Lung cancer has been reported to be the leading cause of cancer‑related mortality worldwide. Cisplatin combination chemotherapy is a standard therapeutic strategy for patients with non‑small cell lung cancer (NSCLC) lacking driver mutations. However, the development of cisplatin resistance is a major obstacle to effective cancer treatment. The cellular mechanisms underlying cisplatin resistance have been previously revealed to be multifunctional. Accordingly, mechanistic analysis and the development of novel therapeutic strategies for cisplatin‑resistant NSCLC are urgently required. The present study mainly focused on the DNA repair mechanisms in cisplatin‑resistant NSCLC cells. Additionally, the effects of an Ecteinascidin (Et) derivative on cisplatin‑resistant cell lines were examined, by using a cisplatin‑resistant NSCLC cell line subjected to nucleotide excision repair (NER) pathway alterations. The results revealed that xeroderma pigmentosum group F‑complementing protein (XPF) mRNA expression was strongly associated with cisplatin resistance in cisplatin‑resistant NSCLC cell lines. XPF silencing significantly restored the sensitivity of cisplatin‑resistant PC‑14/CDDP cells to the drug. A potent anticancer effect of Et was observed in the cisplatin‑resistant cell line (PC‑14/CDDP), in which the NER pathway was altered. On the whole, these findings revealed that the expression levels of NER pathway‑related genes, including XPF, may have potential as biomarkers of cisplatin resistance. It was also suggested that Et may be a very promising compound for the development of novel anticancer drugs for the treatment of cisplatin‑resistant lung cancer.

Identification of Antimycobacterial Natural Products from a Library of Marine Invertebrate Extracts

Tuberculosis (TB) remains a public health crisis, requiring the urgent identification of new anti-mycobacterial drugs. We screened several organic and aqueous marine invertebrate extracts for their in vitro inhibitory activity against the causative organism, Mycobacterium tuberculosis. Here, we report the results obtained for 54 marine invertebrate extracts. The chemical components of two of the extracts were dereplicated, using ¹H NMR and HR-LCMS with GNPS molecular networking, and these extracts were further subjected to an activity-guided isolation process to purify the bioactive components. Hyrtios reticulatus yielded heteronemin 1 and Jaspis splendens was found to produce the bengamide class of compounds, of which bengamides P 2 and Q 3 were isolated, while a new derivative, bengamide S 5, was putatively identified and its structure predicted, based on the similarity of its MS/MS fragmentation pattern to those of other bengamides. The isolated bioactive metabolites and semi-pure fractions exhibited M. tuberculosis growth inhibitory activity, in the range <0.24 to 62.50 µg/mL. This study establishes the bengamides as potent antitubercular compounds, with the first report of whole-cell antitubercular activity of bengamides P 2 and Q 3.

A brief overview of classical natural product drug synthesis and bioactivity

This manuscript briefly overviewed the total synthesis and structure–activity relationship studies of eight classical natural products, which emphasizes the important role of total synthesis in natural product-based drug development.

Antibacterial Bicyclic Fatty Acids from a Korean Colonial Tunicate Didemnum sp

Five new bicyclic carboxylic acids were obtained by antibacterial activity-guided isolation from a Korean colonial tunicate Didemnum sp. Their structures were elucidated by the interpretation of NMR, MS and CD spectroscopic data. They all belong to the class of aplidic acids. Three of them were amide derivatives (1-3), and the other two were dicarboxylic derivatives (4 and 5). The absolute configurations were determined by a bisignate pattern of CD spectroscopy, which revealed that the absolute configurations of amides were opposite to those of dicarboxylates at every stereogenic centers. Compound 2 exhibited the most potent antibacterial activity (MIC, 2 μg/mL).

Marine Power on Cancer: Drugs, Lead Compounds, and Mechanisms

Worldwide, 19.3 million new cancer cases and almost 10.0 million cancer deaths occur each year. Recently, much attention has been paid to the ocean, the largest biosphere of the earth that harbors a great many different organisms and natural products, to identify novel drugs and drug candidates to fight against malignant neoplasms. The marine compounds show potent anticancer activity in vitro and in vivo, and relatively few drugs have been approved by the U.S. Food and Drug Administration for the treatment of metastatic malignant lymphoma, breast cancer, or Hodgkin's disease. This review provides a summary of the anticancer effects and mechanisms of action of selected marine compounds, including cytarabine, eribulin, marizomib, plitidepsin, trabectedin, zalypsis, adcetris, and OKI-179. The future development of anticancer marine drugs requires innovative biochemical biology approaches and introduction of novel therapeutic targets, as well as efficient isolation and synthesis of marine-derived natural compounds and derivatives.

Symbiotic Associations in Ascidians: Relevance for Functional Innovation and Bioactive Potential

Associations between different organisms have been extensively described in terrestrial and marine environments. These associations are involved in roles as diverse as nutrient exchanges, shelter or adaptation to adverse conditions. Ascidians are widely dispersed marine invertebrates associated to invasive behaviours. Studying their microbiomes has interested the scientific community, mainly due to its potential for bioactive compounds production-e.g., ET-73 (trabectedin, Yondelis), an anticancer drug. However, these symbiotic interactions embrace several environmental and biological functions with high ecological relevance, inspiring diverse biotechnological applications. We thoroughly reviewed microbiome studies (microscopic to metagenomic approaches) of around 171 hosts, worldwide dispersed, occurring at different domains of life (Archaea, Bacteria, Eukarya), to illuminate the functions and bioactive potential of associated organisms in ascidians. Associations with Bacteria are the most prevalent, namely with Cyanobacteria, Proteobacteria, Bacteroidetes, Actinobacteria and Planctomycetes phyla. The microbiomes of ascidians belonging to Aplousobranchia order have been the most studied. The integration of worldwide studies characterizing ascidians' microbiome composition revealed several functions including UV protection, bioaccumulation of heavy metals and defense against fouling or predators through production of natural products, chemical signals or competition. The critical assessment and characterization of these communities is extremely valuable to comprehend their biological/ecological role and biotechnological potential.

Insight into the sequence-specific elements leading to increased DNA bending and ligase-mediated circularization propensity by antitumor trabectedin

DNA curvature is the result of a combination of both intrinsic features of the double helix and external distortions introduced by the environment and the binding of proteins or drugs. The propensity of certain double-stranded DNA (dsDNA) sequences to bend is essential in crucial biological processes, such as replication and transcription, in which proteins are known to either recognize noncanonical DNA conformations or promote their formation upon DNA binding. Trabectedin (Yondelis®) is a clinically used antitumor drug which, following covalent bond formation with the 2-amino group of guanine, induces DNA curvature and enhances the circularization ratio, upon DNA ligation, of several dsDNA constructs but not others. By means of unrestrained molecular dynamics simulations using explicitly solvated all-atom models, we rationalize these experimental findings in structural terms and shed light on the crucial, albeit possibly underappreciated, role played by T4 DNA ligase in stabilizing a bent DNA conformation prior to cyclization. Taken together, our results expand our current understanding on how DNA shape modification by trabectedin may affect both the sequence-specific recognition by transcription factors to promoter sites and RNA polymerase II binding.

Marine Natural Products from Tunicates and Their Associated Microbes

Marine tunicates are identified as a potential source of marine natural products (MNPs), demonstrating a wide range of biological properties, like antimicrobial and anticancer activities. The symbiotic relationship between tunicates and specific microbial groups has revealed the acquisition of microbial compounds by tunicates for defensive purpose. For instance, yellow pigmented compounds, "tambjamines", produced by the tunicate, Sigillina signifera (Sluiter, 1909), primarily originated from their bacterial symbionts, which are involved in their chemical defense function, indicating the ecological role of symbiotic microbial association with tunicates. This review has garnered comprehensive literature on MNPs produced by tunicates and their symbiotic microbionts. Various sections covered in this review include tunicates' ecological functions, biological activities, such as antimicrobial, antitumor, and anticancer activities, metabolic origins, utilization of invasive tunicates, and research gaps. Apart from the literature content, 20 different chemical databases were explored to identify tunicates-derived MNPs. In addition, the management and exploitation of tunicate resources in the global oceans are detailed for their ecological and biotechnological implications.

Natural products: A lead for drug discovery and development

Natural products are used since ancient times in folklore for the treatment of various ailments. Plant-derived products have been recognized for many years as a source of therapeutic agents and structural diversity. A literature survey has been carried out to determine the utility of natural molecules and their modified analogs or derivatives as pharmacological active entities. This review presents a study on the importance of natural products in terms of drug discovery and development. It describes how the natural components can be utilized after small modifications in new perspectives. Various new modifications in structure offer a unique opportunity to establish a new molecular entity with better pharmacological potential. It was concluded that in this current era, new attempts are taken to utilize the compounds derived from natural sources as novel drug candidates, with a focus to find and discover new effective molecules that were referred to as "new entities of natural product drug discovery."

Chemical Research on Antitumor Isoquinoline Marine Natural Products and Related Compounds

The biologically active, naturally occurring 1,2,3,4-tetrahydroisoquinoline-quinone (THIQ) family members isolated from Actinomycetes and marine organisms have been studied thoroughly over the past five decades. Among them, marine natural products along with their reduced compounds, such as renieramycins and ecteinascidins, have attracted interest due to their fantastic structures and meager availability in nature as well as their potent antitumor profiles. As part of our search for new anticancer metabolites through the isolation and characterization of anticancer THIQ compounds from Thai marine animals, we have developed a fascinating THIQ natural product chemistry and medicinal chemistry based on knowledge of the chemistry of saframycin antibiotics as well as their isolation, characterization, transformation, partial synthesis, and total synthesis. This review mainly presents our contributions during 1999-2019 to the field of research on biologically active renieramycin along with ecteinascidin marine natural products.

Renieramycin-type alkaloids from marine-derived organisms: Synthetic chemistry, biological activity and structural modification

Marine natural products are known for their diverse chemical structures and extensive bioactivities. Renieramycins, the member of tetrahydroisoquinoline family of marine natural products, arouse interests because of their strong antitumor activities and similar structures to the first marine antitumor agent ecteinascidin-743, approved by the European Union. According to the literatures, researches on the pharmacological activities of renieramycins mainly focus on their antitumor activities. In addition, by structural modification, derivatives of renieramycins show stronger antiproliferative activity and less accidental necrosis activity on cells. Nevertheless, the difficulties in extraction and separation hinder their further development. Hence, the synthetic chemistry work of renieramycins plays a key role in their further development. In this review, currently reported researches on the synthetic chemistry, pharmacological activities and structural modification of renieramycins are summarized, which will benefit future drug development and innovation.

A look around the West Indies: The spices of life are secondary metabolites

Natural products possess a wide range of bioactivities with potential for therapeutic usage. While the distribution of these molecules can vary greatly there is some correlation that exists between the biodiversity of an environment and the uniqueness and concentration of natural products found in that region or area. The Caribbean and pan-Caribbean area is home to thousands of species of endemic fauna and flora providing huge potential for natural product discovery and by way, potential leads for drug development. This can especially be said for marine natural products as many of are rapidly diluted through diffusion once released and therefore are highly potent to achieve long reaching effects. This review seeks to highlight a small selection of marine natural products from the Caribbean region which possess antiproliferative, anti-inflammatory and antipathogenic properties while highlighting any synthetic efforts towards bioactive analogs.

Seasonal dynamics and starvation impact on the gut microbiome of urochordate ascidian Halocynthia roretzi

Background

Gut microbiota plays important roles in host animal metabolism, homeostasis and environmental adaptation. However, the interplay between the gut microbiome and urochordate ascidian, the most closet relative of vertebrate, remains less explored. In this study, we characterized the gut microbial communities of urochordate ascidian (Halocynthia roretzi) across the changes of season and starvation stress using a comprehensive set of omic approaches including 16S rRNA gene amplicon sequencing, shotgun metagenomics, metabolomic profiling, and transcriptome sequencing.

Results

The 16S rRNA gene amplicon profiling revealed that ascidians harbor indigenous gut microbiota distinctly different to the marine microbial community and significant variations in composition and abundance of gut bacteria, with predominant bacterial orders representing each season. Depressed alpha-diversities of gut microbiota were observed across starvation stress when compared to the communities in aquafarm condition. Synechococcales involving photosynthesis and its related biosynthesis was reduced in abundance while the enrichments of Xanthomonadales and Legionellales may facilitate bile acid biosynthesis during starvation. Metabolomics analysis found that long chain fatty acids, linolenic acid, cyanoamino acid, and pigments derived from gut bacteria were upregulated, suggesting a beneficial contribution of the gut microbiome to the ascidian under starvation stress.

Conclusions

Our findings revealed seasonal variation of ascidian gut microbiota. Defense and energy-associated metabolites derived from gut microbiome may provide an adaptive interplay between gut microbiome and ascidian host that maintains a beneficial metabolic system across season and starvation stress. The diversity-generating metabolisms from both microbiota and host might lead to the co-evolution and environmental adaptation.

Graphical Abstract

Shotgun Proteomics of Ascidians Tunic Gives New Insights on Host-Microbe Interactions by Revealing Diverse Antimicrobial Peptides

Ascidians are marine invertebrates associated with diverse microbial communities, embedded in their tunic, conferring special ecological and biotechnological relevance to these model organisms used in evolutionary and developmental studies. Next-generation sequencing tools have increased the knowledge of ascidians’ associated organisms and their products, but proteomic studies are still scarce. Hence, we explored the tunic of three ascidian species using a shotgun proteomics approach. Proteins extracted from the tunic of Ciona sp., Molgula sp., and Microcosmus sp. were processed using a nano LC-MS/MS system (Ultimate 3000 liquid chromatography system coupled to a Q-Exactive Hybrid Quadrupole-Orbitrap mass spectrometer). Raw data was searched against UniProtKB – the Universal Protein Resource Knowledgebase (Bacteria and Metazoa section) using Proteome Discoverer software. The resulting proteins were merged with a non-redundant Antimicrobial Peptides (AMPs) database and analysed with MaxQuant freeware. Overall, 337 metazoan and 106 bacterial proteins were identified being mainly involved in basal metabolism, cytoskeletal and catalytic functions. 37 AMPs were identified, most of them attributed to eukaryotic origin apart from bacteriocins. These results and the presence of “Biosynthesis of antibiotics” as one of the most highlighted pathways revealed the tunic as a very active tissue in terms of bioactive compounds production, giving insights on the interactions between host and associated organisms. Although the present work constitutes an exploratory study, the approach employed revealed high potential for high-throughput characterization and biodiscovery of the ascidians’ tunic and its microbiome.

Antitumoral compounds from vertebrate sister group: A review of Mediterranean ascidians

Among the diseases that afflict the human population, cancer is one for which many drug treatments are not yet known or effective. Moreover, the pharmacological treatments used often create serious side effects in sick patients and for this reason, it is essential to find effective and less harmful treatments. To date, marine biodiversity is a real source of metabolites with antitumoral activity and among invertebrates' ascidians have been the main source to obtain them. Mediterranean area is the richest in biodiversity and contains several ascidian species used in drugs development during the years. However, many more Mediterranean ascidian species have not been studied and could be a source of useful bioactive compounds. This review aims to summarize the scientific studies that analyzed the antitumor compounds obtained from different Mediterranean ascidians species, encouraging them to search further compounds in other new species to improve pharmacological treatments and human population life.

Highlights of marine natural products having parallel scaffolds found from marine-derived bacteria, sponges, and tunicates

Marine-derived bacteria are a prolific source of a wide range of structurally diverse natural products. This review, dedicated to Professor William Fenical, begins by showcasing many seminal discoveries made at the University of California San Diego from marine-derived actinomycetes. Discussed early on is the 20-year journey of discovery and advancement of the seminal actinomycetes natural product salinosporamide A into Phase III anticancer clinical trials. There are many fascinating parallels discussed that were gleaned from the comparative literature of marine sponge, tunicate, and bacteria-derived natural products. Identifying bacterial biosynthetic machinery housed in sponge and tunicate holobionts through both culture-independent and culture-dependent approaches is another important and expanding subject that is analyzed. Work reviewed herein also evaluates the hypotheses that many marine invertebrate-derived natural products are biosynthesised by associated or symbiotic bacteria. The insights and outcomes from metagenomic sequencing and synthetic biology to expand molecule discovery continue to provide exciting outcomes and they are predicted to be the source of the next generation of novel marine natural product chemical scaffolds.

Recent progress toward the asymmetric synthesis of carbon-substituted piperazine pharmacophores and oxidative related heterocycles

The piperazine drugs are mostly N-substituted compared to only a few C-substituted drugs. To explore this unknown chemical space, asymmetric syntheses of C-substituted piperazines is the subject of this review.

The important requirement for approval of a new drug, in case it happens to be chiral, is that both enantiomers of the drug should be studied in detail, which has led synthetic organic and medicinal chemists to focus their attention on the development of new methods for asymmetric synthesis especially of relevant saturated N-heterocycles. On the other hand, the piperazine ring, besides defining a major class of saturated N-heterocycles, has been classified as a privileged structure in medicinal chemistry, since it is more than frequently found in biologically active compounds including several marketed blockbuster drugs such as Glivec (imatinib) and Viagra (sildenafil). Indeed, 13 of the 200 best-selling small molecule drugs in 2012 contained a piperazine ring. Nevertheless, analysis of the piperazine substitution pattern reveals a lack of structural diversity, with almost every single drug in this category (83%) containing a substituent at both the N1- and N4-positions compared to a few drugs having a substituent at any other position (C2, C3, C5, and C6). Significant chemical space that is closely related to that known to be biologically relevant, therefore, remains unexplored. In order to explore this chemical space, efficient and asymmetric syntheses of carbon-substituted piperazines and related heterocycles must be designed and developed. Initial, recent efforts toward the implementation of this particular target are in fact the subject of this review.

Screening Marine Natural Products for New Drug Leads against Trypanosomatids and Malaria

Neglected Tropical Diseases (NTD) represent a serious threat to humans, especially for those living in poor or developing countries. Almost one-sixth of the world population is at risk of suffering from these diseases and many thousands die because of NTDs, to which we should add the sanitary, labor and social issues that hinder the economic development of these countries. Protozoan-borne diseases are responsible for more than one million deaths every year. Visceral leishmaniasis, Chagas disease or sleeping sickness are among the most lethal NTDs. Despite not being considered an NTD by the World Health Organization (WHO), malaria must be added to this sinister group. Malaria, caused by the apicomplexan parasite Plasmodium falciparum, is responsible for thousands of deaths each year. The treatment of this disease has been losing effectiveness year after year. Many of the medicines currently in use are obsolete due to their gradual loss of efficacy, their intrinsic toxicity and the emergence of drug resistance or a lack of adherence to treatment. Therefore, there is an urgent and global need for new drugs. Despite this, the scant interest shown by most of the stakeholders involved in the pharmaceutical industry makes our present therapeutic arsenal scarce, and until recently, the search for new drugs has not been seriously addressed. The sources of new drugs for these and other pathologies include natural products, synthetic molecules or repurposing drugs. The most frequent sources of natural products are microorganisms, e.g., bacteria, fungi, yeasts, algae and plants, which are able to synthesize many drugs that are currently in use (e.g. antimicrobials, antitumor, immunosuppressants, etc.). The marine environment is another well-established source of bioactive natural products, with recent applications against parasites, bacteria and other pathogens which affect humans and animals. Drug discovery techniques have rapidly advanced since the beginning of the millennium. The combination of novel techniques that include the genetic modification of pathogens, bioimaging and robotics has given rise to the standardization of High-Performance Screening platforms in the discovery of drugs. These advancements have accelerated the discovery of new chemical entities with antiparasitic effects. This review presents critical updates regarding the use of High-Throughput Screening (HTS) in the discovery of drugs for NTDs transmitted by protozoa, including malaria, and its application in the discovery of new drugs of marine origin.

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

Construction of sulfur-containing moieties in the total synthesis of natural products

This review surveys the total syntheses of sulfur-containing natural products where sulfur atoms are introduced with different sulfurization agents to construct related sulfur-containing moieties.

Enriching cancer pharmacology with drugs of marine origin

Marine natural products have proven, over the last half-century, to be effective biological modulators. These molecules have revealed new targets for cancer therapy as well as dissimilar modes of action within typical classes of drugs. In this scenario, innovation from marine-based pharmaceuticals has helped advance cancer chemotherapy in many aspects, as most of these are designated as first-in-class drugs. Here, by examining the path from discovery to development of clinically approved drugs of marine origin for cancer treatment-cytarabine (Cytosar-U®), trabectedin (Yondelis®), eribulin (Halaven®), brentuximab vedotin (Adcetris®), and plitidepsin (Aplidin®)- together with those in late clinical trial phases-lurbinectedin, plinabulin, marizomib, and plocabulin-the present review offers a critical analysis of the contributions given by these new compounds to cancer pharmacotherapy.

Convergent Formal Synthesis of Ecteinascidin 743

A concise formal synthesis of ecteinascidin 743 is described. Key features involve the coupling of the multisubstituted tetrahydroisoquinoline and phenylalaninol moieties via a regio- and stereoselective Pictet-Spengler cyclization as well as the subsequent chemoselective MOM protection of the phenol group, which opens a rapid access to the desirable pentacycle. The synthesis successfully delivered the advanced intermediate with the characteristic macrolactone from sesamol in 23 steps.

Marine-Derived Anticancer Agents: Clinical Benefits, Innovative Mechanisms, and New Targets

The role of the marine environment in the development of anticancer drugs has been widely reviewed, particularly in recent years. However, the innovation in terms of clinical benefits has not been duly emphasized, although there are important breakthroughs associated with the use of marine-derived anticancer agents that have altered the current paradigm in chemotherapy. In addition, the discovery and development of marine drugs has been extremely rewarding with significant scientific gains, such as the discovery of new anticancer mechanisms of action as well as novel molecular targets. Approximately 50 years since the approval of cytarabine, the marine-derived anticancer pharmaceutical pipeline includes four approved drugs and eighteen agents in clinical trials, six of which are in late development. Thus, the dynamic pharmaceutical pipeline consisting of approved and developmental marine-derived anticancer agents offers new hopes and new tools in the treatment of patients afflicted with previously intractable types of cancer.

Structural Simplification of Natural Products

Natural products (NPs) are important sources of clinical drugs due to their structural diversity and biological prevalidation. However, the structural complexity of NPs leads to synthetic difficulties, unfavorable pharmacokinetic profiles, and poor drug-likeness. Structural simplification by truncating unnecessary substructures is a powerful strategy for overcoming these limitations and improving the efficiency and success rate of NP-based drug development. Herein, we will provide a comprehensive review of the structural simplification of NPs with a focus on design strategies, case studies, and new technologies. In particular, a number of successful examples leading to marketed drugs or drug candidates will be discussed in detail to illustrate how structural simplification is applied in lead optimization of NPs.

Biological and Chemical Diversity of Ascidian-Associated Microorganisms

Ascidians are a class of sessile filter-feeding invertebrates, that provide unique and fertile niches harboring various microorganisms, such as bacteria, actinobacteria, cyanobacteria and fungi. Over 1000 natural products, including alkaloids, cyclic peptides, and polyketides, have been isolated from them, which display diverse properties, such as antibacterial, antifungal, antitumor, and anti-inflammatory activities. Strikingly, direct evidence has confirmed that ~8% of natural products from ascidians are actually produced by symbiotic microorganisms. In this review, we present 150 natural products from microorganisms associated with ascidians that have been reported up to 2017.