Cytotoxic diterpenoid pseudodimers from the Korean sponge Phorbas gukhulensis

Chemical and biological diversity of new natural products from marine sponges: a review (2009-2018)

Marine sponges are productive sources of bioactive secondary metabolites with over 200 new compounds isolated each year, contributing 23% of approved marine drugs so far. This review describes statistical research, structural diversity, and pharmacological activity of sponge derived new natural products from 2009 to 2018. Approximately 2762 new metabolites have been reported from 180 genera of sponges this decade, of which the main structural types are alkaloids and terpenoids, accounting for 50% of the total. More than half of new molecules showed biological activities including cytotoxic, antibacterial, antifungal, antiviral, anti-inflammatory, antioxidant, enzyme inhibition, and antimalarial activities. As summarized in this review, macrolides and peptides had higher proportions of new bioactive compounds in new compounds than other chemical classes. Every chemical class displayed cytotoxicity as the dominant activity. Alkaloids were the major contributors to antibacterial, antifungal, and antioxidant activities while steroids were primarily responsible for pest resistance activity. Alkaloids, terpenoids, and steroids displayed the most diverse biological activities. The statistic research of new compounds by published year, chemical class, sponge taxonomy, and biological activity are presented. Structural novelty and significant bioactivities of some representative compounds are highlighted. Marine sponges are rich sources of novel bioactive compounds and serve as animal hosts for microorganisms, highlighting the undisputed potential of sponges in the marine drugs research and development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00132-3.

Total Synthesis of Gukulenin B via Sequential Tropolone Functionalizations

The synthesis of functionalized aromatic compounds is a central theme of research for modern organic chemistry. Despite the increasing finesse in the functionalization of five- and six-membered aromatic rings, their seven-membered-ring sibling, tropolone (2-hydroxy-2,4,6-cycloheptatrien-1-one), remains a challenging target for synthetic derivatization. This challenge primarily emanates from the unique structural and chemical properties of tropolonoid compounds, which often lead to unexpected and undesired reaction outcomes under conditions developed for the functionalizations of other aromatic moieties. Herein, we describe the total synthesis of one of the most complex natural tropolonoids, gukulenin B. Our synthetic route features a series of site-selective aromatic C-H bond functionalizations and C-C bond formations, whose reaction conditions are judiciously tuned to allow uncompromised performance on the tropolone nucleus. The flexibility and modularity of our synthesis are expected to facilitate further synthetic and biological studies of the gukulenin family of cytotoxins. In addition, the methods and tactics developed herein for the functionalization of the tropolone moiety could inspire and enable chemists of multiple disciplines to take advantage of this privileged yet underexplored structural motif.

Exploring Chemical Diversity of Phorbas Sponges as a Source of Novel Lead Compounds in Drug Discovery

Porifera, commonly referred to as marine sponges, are acknowledged as major producers of marine natural products (MNPs). Sponges of the genus Phorbas have attracted much attention over the years. They are widespread in all continents, and several structurally unique compounds have been identified from this species. Terpenes, mainly sesterterpenoids, are the major secondary metabolites isolated from Phorbas species, even though several alkaloids and steroids have also been reported. Many of these compounds have presented interesting biological activities. Particularly, Phorbas sponges have been demonstrated to be a source of cytotoxic metabolites. In addition, MNPs exhibiting cytostatic, antimicrobial, and anti-inflammatory activities have been isolated and structurally characterized. This review provides an overview of almost 130 secondary metabolites from Phorbas sponges and their biological activities, and it covers the literature since the first study published in 1993 until November 2021, including approximately 60 records. The synthetic routes to the most interesting compounds are briefly outlined.

Bioactive natural products from marine sponges belonging to family Hymedesmiidae

Natural products of marine origin exhibit extensive biological activities, and display a vital role in the exploration of new compounds for drug development. Marine sponges have been reported at the top with respect to the discovery of biologically active metabolites that have potential pharmaceutical applications. The family Hymedesmiidae belonging to the Demospongiae class includes ten accepted genera, of which four genera were explored for their bioactive metabolites, namely Phorbas, Hamigera, Hemimycale, and Kirkpatrickia. Genus Phorbas has received more attention due to the isolation of various classes of compounds with unique structures mainly diterpenes, alkaloids, sesterterpenes, and steroids that exhibited diverse biological activities including: antiviral, antimicrobial, and anti-inflammatory, whereas anticancer compounds predominated. This review focuses on the isolated secondary metabolites from family Hymedesmiidae with their biological potential and covers the literature from 1989 to 2020.

Natural products of marine origin exhibit extensive biological activities, and display a vital role in the exploration of new compounds for drug development.

Integrated analytical workflow for chromatographic profiling and metabolite annotation of a cytotoxic Phorbas amaranthus extract

Phorbas is a widely studied genus of marine sponge and produce structurally rich cytotoxic metabolites. Still, only few studies have assessed metabolites present in Brazilian species. To circumvent redundancy, in this work, we applied and herein report the use of a scouting liquid chromatographic system associate to the design of experiment produced by the DryLab® software to obtain a fast and efficient chromatographic separation of the active hexane fraction, further enabling untargeted high-resolution mass spectrometry (HRMS) data. To this end, a crude hydroalcoholic extract of the sponge Phorbas amaranthus collected in Brazilian coast was prepared and partitioned. The cytotoxicity of the crude extract and the fractions was evaluated using tumor cell culture models. Fragmentation pathways assembled from HRMS data allowed the annotation of 18 known Phorbas metabolites, while 17 metabolites were inferred based on Global Natural Product Social Molecular Networking (GNPS), matching with a further 29 metabolites annotated through molecular subnetwork. The workflow employed demonstrates that chromatographic method development can be accelerated by the use of automated scouting systems and DryLab®, which is useful for profiling natural product libraries, as well as data curation by molecular clusters and should be incorporated to the tools of natural product chemists.

Anticancer Activity of Gukulenin A Isolated from the Marine Sponge Phorbas gukhulensis In Vitro and In Vivo

Gukulenin A is a bis-tropolone tetraterpenoid isolated from the marine sponge Phorbas gukhulensis. In this study, we examined the anticancer activities of gukulenin A in ovarian cancer cell lines (A2780, SKOV3, OVCAR-3, and TOV-21G) and in an ovarian cancer mouse model generated by injecting A2780 cells. We found that gukulenin A suppressed tumor growth in A2780-bearing mice. Gukulenin A markedly inhibited cell viability in four ovarian cancer cell lines, including the A2780 cell line. Gukulenin A treatment increased the fraction of cells accumulated at the sub G1 phase in a dose-dependent manner and the population of annexin V-positive cells, suggesting that gukulenin A induces apoptotic cell death in ovarian cancer cells. In addition, gukulenin A triggered the activation of caspase-3, -8, and -9, and caspase inhibitors attenuated gukulenin A-induced A2780 cell death. The results suggest that gukulenin A may be a potential therapeutic agent for ovarian cancer.

Progress toward the Total Synthesis of Gukulenin A: Photochemically Triggered Two-Carbon Ring Expansion Key to α-Tropolonic Ether Synthesis

The ex-chiral-pool synthesis of an advanced gukulenin A precursor from (-)-piperitone is revealed. Key C/C connecting maneuvers to the synthesis of a C₂ dissymmetric bis(α-tropolonic) ether building block are a ring-contracting Meinwald rearrangement, a photochemically triggered two-carbon ring expansion, and a homodimerization by cross-metathesis.

Isolation, Biosynthesis and Chemical Modifications of Rubterolones A-F: Rare Tropolone Alkaloids from Actinomadura sp. 5-2

The discovery of six new, highly substituted tropolone alkaloids, rubterolones A-F, from Actinomadura sp. 5-2, isolated from the gut of the fungus-growing termite Macrotermes natalensis is reported. Rubterolones were identified by using fungus-bacteria challenge assays and a HRMS-based dereplication strategy, and characterised by NMR and HRMS analyses and by X-ray crystallography. Feeding experiments and subsequent chemical derivatisation led to a first library of rubterolone derivatives (A-L). Genome sequencing and comparative analyses revealed their putative biosynthetic pathway, which was supported by feeding experiments. This study highlights how gut microbes can present a prolific source of secondary metabolites.

Marine natural products

This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) 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 (1163 for 2013), 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.