Tricyclic guanidine alkaloids from the marine sponge Acanthella cavernosa that stabilize the tumor suppressor PDCD4

A review of natural products and small-molecule therapeutics acting on central nervous system malignancies: Approaches for drug development, targeting pathways, clinical trials, and challenges

In 2021, the World Health Organization released the fifth edition of the central nervous system (CNS) tumor classification. This classification uses histopathology and molecular pathogenesis to group tumors into more biologically and molecularly defined entities. The prognosis of brain cancer, particularly malignant tumors, has remained poor worldwide, approximately 308,102 new cases of brain and other CNS tumors were diagnosed in the year 2020, with an estimated 251,329 deaths. The cost and time-consuming nature of studies to find new anticancer agents makes it necessary to have well-designed studies. In the present study, the pathways that can be targeted for drug development are discussed in detail. Some of the important cellular origins, signaling, and pathways involved in the efficacy of bioactive molecules against CNS tumorigenesis or progression, as well as prognosis and common approaches for treatment of different types of brain tumors, are reviewed. Moreover, different study tools, including cell lines, in vitro, in vivo, and clinical trial challenges, are discussed. In addition, in this article, natural products as one of the most important sources for finding new chemotherapeutics were reviewed and over 700 reported molecules with efficacy against CNS cancer cells are gathered and classified according to their structure. Based on the clinical trials that have been registered, very few of these natural or semi-synthetic derivatives have been studied in humans. The review can help researchers understand the involved mechanisms and design new goal-oriented studies for drug development against CNS malignancies.

Genus Acanthella-A Wealthy Treasure: Secondary Metabolites, Synthesis, Biosynthesis, and Bioactivities

Marine sponges are multicellular and primitive animals that potentially represent a wealthy source of novel drugs. The genus Acanthella (family Axinellidae) is renowned to produce various metabolites with various structural characteristics and bioactivities, including nitrogen-containing terpenoids, alkaloids, and sterols. The current work provides an up-to-date literature survey and comprehensive insight into the reported metabolites from the members of this genus, as well as their sources, biosynthesis, syntheses, and biological activities whenever available. In the current work, 226 metabolites have been discussed based on published data from the period from 1974 to the beginning of 2023 with 90 references.

Marine Natural Products from Flora and Fauna of the Western Australian Coast: Taxonomy, Isolation and Biological Activity

Marine natural products occurring along the Western Australian coastline are the focus of this review. Western Australia covers one-third of the Australian coast, from tropical waters in the far north of the state to cooler temperate and Antarctic waters in the south. Over 40 years of research has resulted in the identification of a number of different types of secondary metabolites including terpenoids, alkaloids, polyketides, fatty acid derivatives, peptides and arsenic-containing natural products. Many of these compounds have been reported to display a variety of bioactivities. A description of the compound classes and their associated bioactivities from marine organisms found along the Western Australian coastline is presented.

Fused Tricyclic Guanidine Alkaloids: Insights into Their Structure, Synthesis and Bioactivity

A marine natural product possesses a diverse and unique scaffold that contributes to a vast array of bioactivities. Tricyclic guanidine alkaloids are a type of scaffold found only in marine natural products. These rare skeletons exhibit a wide range of biological applications, but their synthetic approaches are still limited. Various stereochemical assignments of the compounds remain unresolved. Batzelladine and ptilocaulins are an area of high interest in research on tricyclic guanidine alkaloids. In addition, mirabilins and netamines are among the other tricyclic guanidine alkaloids that contain the ptilocaulin skeleton. Due to the different structural configurations of batzelladine and ptilocaulin, these two main skeletons are afforded attention in many reports. These two main skeletons exhibit different kinds of compounds by varying their ester chain and sidechain. The synthetic approaches to tricyclic guanidine alkaloids, especially the batzelladine and ptilocaulin skeletons, are discussed. Moreover, this review compiles the first and latest research on the synthesis of these compounds and their bioactivities, dating from the 1980s to 2022.

Anti-inflammatory aromadendrane- and cadinane-type sesquiterpenoids from the South China Sea sponge Acanthella cavernosa

One new aromadendrane-type sesquiterpenoid, namely ximaocavernosin P [(+)-1], and three new cadinane-type sesquiterpenoids, namely (+)-maninsigin D [(+)-4], (+)- and (−)-ximaocavernosin Q [(+)- and (−)-5], together with five related known ones [2, 3, (−)-4, 6, and 7], were isolated from the Hainan sponge Acanthella cavernosa. Compounds 4 and 5 were isolated as racemic forms, which were further separated to the corresponding enantiomers [(+)-4/(−)-4 and (+)-5/(−)-5], respectively, by using chiral-phase HPLC. The structures of new compounds were elucidated by extensive spectroscopic analysis and comparison with the reported data. In addition, the absolute configuration of optically pure (+)-1 and 2 were determined by time-dependent density functional theory/electronic circular dichroism (TDDFT-ECD) calculations or X-ray diffraction analysis. A plausible biosynthetic pathway of these sesquiterpenoids and their internal correlation were proposed and discussed. In an in vitro bioassay, (+)-aristolone (3) exhibited promising anti-inflammatory activity by the inhibition of LPS-induced TNF-α and CCL2 release in RAW 264.7 macrophages.

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.

A Soft Spot for Chemistry-Current Taxonomic and Evolutionary Implications of Sponge Secondary Metabolite Distribution

Marine sponges are the most prolific marine sources for discovery of novel bioactive compounds. Sponge secondary metabolites are sought-after for their potential in pharmaceutical applications, and in the past, they were also used as taxonomic markers alongside the difficult and homoplasy-prone sponge morphology for species delineation (chemotaxonomy). The understanding of phylogenetic distribution and distinctiveness of metabolites to sponge lineages is pivotal to reveal pathways and evolution of compound production in sponges. This benefits the discovery rate and yield of bioprospecting for novel marine natural products by identifying lineages with high potential of being new sources of valuable sponge compounds. In this review, we summarize the current biochemical data on sponges and compare the metabolite distribution against a sponge phylogeny. We assess compound specificity to lineages, potential convergences, and suitability as diagnostic phylogenetic markers. Our study finds compound distribution corroborating current (molecular) phylogenetic hypotheses, which include yet unaccepted polyphyly of several demosponge orders and families. Likewise, several compounds and compound groups display a high degree of lineage specificity, which suggests homologous biosynthetic pathways among their taxa, which identifies yet unstudied species of this lineage as promising bioprospecting targets.

Metabolites from Marine Sponges and Their Potential to Treat Malarial Protozoan Parasites Infection: A Systematic Review

Malaria is an infectious disease caused by protozoan parasites of the Plasmodium genus through the bite of female Anopheles mosquitoes, affecting 228 million people and causing 415 thousand deaths in 2018. Artemisinin-based combination therapies (ACTs) are the most recommended treatment for malaria; however, the emergence of multidrug resistance has unfortunately limited their effects and challenged the field. In this context, the ocean and its rich biodiversity have emerged as a very promising resource of bioactive compounds and secondary metabolites from different marine organisms. This systematic review of the literature focuses on the advances achieved in the search for new antimalarials from marine sponges, which are ancient organisms that developed defense mechanisms in a hostile environment. The principal inclusion criterion for analysis was articles with compounds with IC₅₀ below 10 µM or 10 µg/mL against P. falciparum culture. The secondary metabolites identified include alkaloids, terpenoids, polyketides endoperoxides and glycosphingolipids. The structural features of active compounds selected in this review may be an interesting scaffold to inspire synthetic development of new antimalarials for selectively targeting parasite cell metabolism.

Control Mechanisms of the Tumor Suppressor PDCD4: Expression and Functions

PDCD4 is a novel tumor suppressor to show multi-functions inhibiting cell growth, tumor invasion, metastasis, and inducing apoptosis. PDCD4 protein binds to the translation initiation factor eIF4A, some transcription factors, and many other factors and modulates the function of the binding partners. PDCD4 downregulation stimulates and PDCD4 upregulation inhibits the TPA-induced transformation of cells. However, PDCD4 gene mutations have not been found in tumor cells but gene expression was post transcriptionally downregulated by micro environmental factors such as growth factors and interleukins. In this review, we focus on the suppression mechanisms of PDCD4 protein that is induced by the tumor promotors EGF and TPA, and in the inflammatory conditions. PDCD4-protein is phosphorylated at 2 serines in the SCF^βTRCP ubiquitin ligase binding sequences via EGF and/or TPA induced signaling pathway, ubiquitinated, by the ubiquitin ligase and degraded in the proteasome system. The PDCD4 protein synthesis is inhibited by microRNAs including miR21.

Recent Advances in the Isolation, Synthesis and Biological Activity of Marine Guanidine Alkaloids

Marine organisms are prolific resources of guanidine-containing natural products with intriguing structures and promising biological activities. These molecules have therefore attracted the attention of chemists and biologists for their further studies towards potential drug leads. This review focused on the guanidine alkaloids derived from marine sources and discussed the recent progress on their isolation, synthesis and biological activities, covering the literature from the year 2010 to the present.

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) 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 (1378 in 456 papers for 2014), 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.

The chemistry and biology of guanidine natural products

The present review discusses the isolation, structure determination, synthesis, biosynthesis and biological activities of secondary metabolites bearing a guanidine group.

De Novo Asymmetric Synthesis of (+)-Monanchorin

A de novo asymmetric total synthesis of the guanidine alkaloid natural product (+)-monanchorin has been achieved in nine steps from the commodity chemicals furan and caproic acid. The asymmetry of the route was introduced by a Noyori reduction of an acylfuran. In addition, this route relies upon an Achmatowicz rearrangement, a diastereoselective palladium catalyzed glycosylation, reductive amination, and an acid catalyzed bicyclic guanidine mixed acetal formation.