Biological activities of novel polyether antifungals, gambieric acids A and B from a marine dinoflagellate Gambierdiscus toxicus

Phytoplankton Toxins and Their Potential Therapeutic Applications: A Journey toward the Quest for Potent Pharmaceuticals

Phytoplankton are prominent organisms that contain numerous bioactive substances and secondary metabolites, including toxins, which can be valuable to pharmaceutical, nutraceutical, and biotechnological industries. Studies on toxins produced by phytoplankton such as cyanobacteria, diatoms, and dinoflagellates have become more prevalent in recent years and have sparked much interest in this field of research. Because of their richness and complexity, they have great potential as medicinal remedies and biological exploratory probes. Unfortunately, such toxins are still at the preclinical and clinical stages of development. Phytoplankton toxins are harmful to other organisms and are hazardous to animals and human health. However, they may be effective as therapeutic pharmacological agents for numerous disorders, including dyslipidemia, obesity, cancer, diabetes, and hypertension. In this review, we have focused on the properties of different toxins produced by phytoplankton, as well as their beneficial effects and potential biomedical applications. The anticancer properties exhibited by phytoplankton toxins are mainly attributed to their apoptotic effects. As a result, phytoplankton toxins are a promising strategy for avoiding postponement or cancer treatment. Moreover, they also displayed promising applications in other ailments and diseases such as Alzheimer’s disease, diabetes, AIDS, fungal, bacterial, schizophrenia, inflammation, allergy, osteoporosis, asthma, and pain. Preclinical and clinical applications of phytoplankton toxins, as well as future directions of their enhanced nano-formulations for improved clinical efficacy, have also been reviewed.

Identification and characterization of the novel bioactive compounds from microalgae and cyanobacteria for pharmaceutical and nutraceutical applications

Microalgae and cyanobacteria (blue-green algae) are used as food by humans. They have gained a lot of attention in recent years because of their potential applications in biotechnology. Microalgae and cyanobacteria are good sources of many valuable compounds, including important biologically active compounds with antiviral, antibacterial, antifungal, and anticancer activities. Under optimal growth condition and stress factors, algal biomass produce varieties of potential bioactive compounds. In the current review, bioactive compounds production and their remarkable applications such as pharmaceutical and nutraceutical applications along with processes involved in identification and characterization of the novel bioactive compounds are discussed. Comprehensive knowledge about the exploration, extraction, screening, and trading of bioactive products from microalgae and cyanobacteria and their pharmaceutical and other applications will open up new avenues for drug discovery and bioprospecting.

Emerging Optical Materials in Sensing and Discovery of Bioactive Compounds

Optical biosensors are used in numerous applications and analytical fields. Advances in these sensor platforms offer high sensitivity, selectivity, miniaturization, and real-time analysis, among many other advantages. Research into bioactive natural products serves both to protect against potentially dangerous toxic compounds and to promote pharmacological innovation in drug discovery, as these compounds have unique chemical compositions that may be characterized by greater safety and efficacy. However, conventional methods for detecting these biomolecules have drawbacks, as they are time-consuming and expensive. As an alternative, optical biosensors offer a faster, simpler, and less expensive means of detecting various biomolecules of clinical interest. In this review, an overview of recent developments in optical biosensors for the detection and monitoring of aquatic biotoxins to prevent public health risks is first provided. In addition, the advantages and applicability of these biosensors in the field of drug discovery, including high-throughput screening, are discussed. The contribution of the investigated technological advances in the timely and sensitive detection of biotoxins while deciphering the pathways to discover bioactive compounds with great health-promoting prospects is envisaged to meet the increasing demands of healthcare systems.

Toxicity Screening of a Gambierdiscus australes Strain from the Western Mediterranean Sea and Identification of a Novel Maitotoxin Analogue

Dinoflagellate species of the genera Gambierdiscus and Fukuyoa are known to produce ciguatera poisoning-associated toxic compounds, such as ciguatoxins, or other toxins, such as maitotoxins. However, many species and strains remain poorly characterized in areas where they were recently identified, such as the western Mediterranean Sea. In previous studies carried out by our research group, a G. australes strain from the Balearic Islands (Mediterranean Sea) presenting MTX-like activity was characterized by LC-MS/MS and LC-HRMS detecting 44-methyl gambierone and gambieric acids C and D. However, MTX1, which is typically found in some G. australes strains from the Pacific Ocean, was not detected. Therefore, this study focuses on the identification of the compound responsible for the MTX-like toxicity in this strain. The G. australes strain was characterized not only using LC-MS instruments but also N2a-guided HPLC fractionation. Following this approach, several toxic compounds were identified in three fractions by LC-MS/MS and HRMS. A novel MTX analogue, named MTX5, was identified in the most toxic fraction, and 44-methyl gambierone and gambieric acids C and D contributed to the toxicity observed in other fractions of this strain. Thus, G. australes from the Mediterranean Sea produces MTX5 instead of MTX1 in contrast to some strains of the same species from the Pacific Ocean. No CTX precursors were detected, reinforcing the complexity of the identification of CTXs precursors in these regions.

Applications of Transition-Metal-Catalyzed Asymmetric Allylic Substitution in Total Synthesis of Natural Products: An Update

Metal-catalyzed asymmetric allylic substitution (AAS) reaction is one of the most synthetically useful reactions catalyzed by metal complexes for the formation of carbon-carbon and carbon-heteroatom bonds. It comprises the substitution of allylic substrates with a wide range of nucleophiles or S_N 2'-type allylic substitution, which results in the formation of the above-mentioned bonds with high levels of enantioselective induction. AAS reaction tolerates a broad range of functional groups, thus has been successfully applied in the asymmetric synthesis of a wide range of optically pure compounds. This reaction has been extensively used in the total synthesis of several complex molecules, especially natural products. In this review, we try to highlight the applications of metal (Pd, Ir, Mo, or Cu)-catalyzed AAS reaction in the total synthesis of the biologically active natural products, as a key step, updating the subject from 2003 till date.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Toxicity screening of 13 Gambierdiscus strains using neuro-2a and erythrocyte lysis bioassays

Species in the epi-benthic dinoflagellate genus Gambierdiscus produce ciguatoxins (CTXs) and maitotoxins (MTXs), which are among the most potent marine toxins known. Consumption of fish contaminated with sufficient quantities of CTXs causes Ciguatera Fish Poisoning (CFP), the largest cause of non-bacterial food poisoning worldwide. Maitotoxins, which can be found in the digestive system of fish, could also contribute to CFP if such tissues are consumed. Recently, an increasing number of Gambierdiscus species have been identified; yet, little is known about the variation in toxicity among Gambierdiscus strains or species. This study is the first assessment of relative CTX- and MTX-toxicity of Gambierdiscus species from areas as widespread as the North-Eastern Atlantic Ocean, Pacific Ocean and the Mediterranean Sea. A total of 13 strains were screened: (i) seven Pacific strains of G. australes, G. balechii, G. caribaeus, G. carpenteri, G. pacificus, G. scabrosus and one strain of an undetermined species (Gambierdiscus sp. Viet Nam), (ii) five strains from the North-Eastern Atlantic Ocean (two G. australes, a single G. excentricus and two G. silvae strains), and (iii) one G. carolinianus strain from the Mediterranean Sea. Cell pellets of Gambierdiscus were extracted with methanol and the crude extracts partitioned into a CTX-containing dichloromethane fraction and a MTX-containing aqueous methanol fraction. CTX-toxicity was estimated using the neuro-2a cytoxicity assay, and MTX-toxicity via a human erythrocyte lysis assay. Different species were grouped into different ratios of CTX- and MTX-toxicity, however, the ratio was not related to the geographical origin of species (Atlantic, Mediterranean, Pacific). All strains showed MTX-toxicity, ranging from 1.5 to 86pg MTX equivalents (eq) cell^-1. All but one of the strains showed relatively low CTX-toxicity ranging from 0.6 to 50 fg CTX3C eq cell^-1. The exception was the highly toxic G. excentricus strain from the Canary Islands, which produced 1426 fg CTX3C eq cell^-1. As was true for CTX, the highest MTX-toxicity was also found in G. excentricus. Thus, the present study confirmed that at least one species from the Atlantic Ocean demonstrates similar toxicity as the most toxic strains from the Pacific, even if the metabolites in fish have so far been shown to be more toxic in the Pacific Ocean.

Nabscessins A and B, Aminocyclitol Derivatives from Nocardia abscessus IFM 10029T

Two new aminocyclitol amide derivatives, nabscessins A (1) and B (2), were isolated from the culture broth of a pathogenic actinomycete species, Nocardia abscessus IFM 10029^T. The structures of nabscessins A and B were elucidated by spectral studies, and the compounds showed antifungal activity against Cryptococcus neoformans, with IC₅₀ values of 32 and 16 μg/mL, respectively.

Hyrtinadines C and D, New Azepinoindole-Type Alkaloids from a Marine Sponge Hyrtios sp

New bisindole alkaloids, hyrtinadines C (1) and D (2), have been isolated from an Okinawan marine sponge Hyrtios sp. The structures of hyrtinadines C (1) and D (2) were elucidated based on analyses of the spectral data. Hyrtinadines C (1) and D (2) were the relatively rare alkaloids possessing a 3,4-fused azepinoindole skeleton. Hyrtinadines C (1) and D (2) showed antimicrobial activity.

Antimicrobial Compounds from Eukaryotic Microalgae against Human Pathogens and Diseases in Aquaculture

The search for novel compounds of marine origin has increased in the last decades for their application in various areas such as pharmaceutical, human or animal nutrition, cosmetics or bioenergy. In this context of blue technology development, microalgae are of particular interest due to their immense biodiversity and their relatively simple growth needs. In this review, we discuss about the promising use of microalgae and microalgal compounds as sources of natural antibiotics against human pathogens but also about their potential to limit microbial infections in aquaculture. An alternative to conventional antibiotics is needed as the microbial resistance to these drugs is increasing in humans and animals. Furthermore, using natural antibiotics for livestock could meet the consumer demand to avoid chemicals in food, would support a sustainable aquaculture and present the advantage of being environmentally friendly. Using natural and renewable microalgal compounds is still in its early days, but considering the important research development and rapid improvement in culture, extraction and purification processes, the valorization of microalgae will surely extend in the future.

Characterization of a Strain of Fukuyoa paulensis (Dinophyceae) from the Western Mediterranean Sea

A single cell of the dinoflagellate genus Fukuyoa was isolated from the island of Formentera (Balearic Islands, west Mediterranean Sea), cultured, and characterized by morphological and molecular methods and toxin analyses. This is the first report of the Gambierdiscus lineage (genera Fukuyoa and Gambierdiscus) from the western Mediterranean Sea, which is cooler than its eastern basin. Molecular analyses revealed that the Mediterranean strain belongs to F. paulensis and that it bears LSU rDNA sequences identical to New Zealand, Australian, and Brazilian strains. It also shared an identical sequence of the more variable ITS-rDNA with the Brazilian strain. Toxin analyses showed the presence of maitotoxin, 54-deoxyCTX1B, and gambieric acid A. This is the first observation of the two latter compounds in a Fukuyoa strain. Therefore, both Gambierdiscus and Fukuyoa should be considered when as contributing to ciguatera fish poisoning. Different strains of Fukuyoa form a complex of morphologically cryptic lineages where F. paulensis stands as the most distantly related nominal species. The comparison of the ITS2 secondary structures revealed the absence of CBCs among strains. The study of the morphological and molecular traits depicted an unresolved taxonomic scenario impacted by the low strains sampling.

Prenylated benzophenones from Triadenum japonicum

Six new prenylated benzophenones, (-)-nemorosonol (1) and trijapins A-E (2-6), were isolated from the aerial parts of Triadenum japonicum. (-)-Nemorosonol (1) and trijapins A-C (2-4) have a common tricyclo[4.3.1.0(3,7)]decane skeleton, while 1 is an enantiomer of (+)-nemorosonol previously isolated from Clusia nemorosa. The absolute configuration of (-)-nemorosonol (1) was assigned by ECD spectroscopy. Trijapins A-C (2-4) are analogues of 1 possessing an additional tetrahydrofuran ring. Trijapins D (5) and E (6) are prenylated benzophenones with a 1,2-dioxane moiety and a hydroperoxy group, respectively. (-)-Nemorosonol (1) exhibited antimicrobial activity against Escherichia coli (MIC, 8 μg/mL), Staphylococcus aureus (MIC, 16 μg/mL), Bacillus subtilis (MIC, 16 μg/mL), Micrococcus luteus (MIC, 32 μg/mL), Aspergillus niger (IC50, 16 μg/mL), Trichophyton mentagrophytes (IC50, 8 μg/mL), and Candida albicans (IC50, 32 μg/mL), while trijapin D (5) showed antimicrobial activity against C. albicans (IC50, 8 μg/mL).

Concise synthesis of the A/BCD-ring fragment of gambieric acid A

Gambieric acid A (GAA) and its congeners belong to the family of marine polycyclic ether natural products. Their highly complex molecular architecture and unique biological activities have been of intense interest within the synthetic community. We have previously reported the first total synthesis, stereochemical reassignment, and preliminary structure–activity relationships of GAA. Here we disclose a concise synthesis of the A/BCD-ring fragment of GAA. The synthesis started from our previously reported synthetic intermediate that represents the A/B-ring. The C-ring was synthesized via an oxiranyl anion coupling and a 6-endo cyclization, and the D-ring was forged by means of an oxidative lactonization and subsequent palladium-catalyzed functionalization of the lactone ring. In this manner, the number of linear synthetic steps required for the construction of the C- and D-rings was reduced from 22 to 11.

Total synthesis and complete structural assignment of gambieric acid A, a large polycyclic ether marine natural product

More than thirty years after the discovery of polycyclic ether marine natural products, they continue to receive intense attention from the chemical, biological, and pharmacological communities because of their potent biological activities and highly complex molecular architectures. Gambieric acids are intriguing polycyclic ethers that exhibit potent antifungal activity with minimal toxicity against mammals. Despite the recent advances in the synthesis of this class of natural products, gambieric acids remain unconquered due to their daunting structural complexity, which poses a formidable synthetic challenge to organic chemists. This paper reviews our long-term studies on the total synthesis, complete configurational reassignment, and structure-activity relationships of gambieric acid A over the last decade.

Hikiokoshins A-I, diterpenes from the leaves of Isodon japonicus

Diterpenes, hikiokoshins A-I, and twelve known diterpenes were isolated from the leaves of Isodon japonicus (Burm. f.) H. Hara (Lamiaceae). The hikiokoshins A-I possess various skeletons such as ternifonane {hikiokoshin A}, ent-6,7:8,15-diseco-6,8-cyclokauran-7,20-olide {hikiokoshin B}, ent-6,7-secokauran-7,20-olide {hikiokoshin C}, and ent-7,20-epoxykaurane {hikiokoshins D-I}. Their structures were elucidated on the basis of spectroscopic analysis. Antimicrobial activities of hikiokoshins A and B were evaluated.

Taurospongins B and C, new acetylenic fatty acid derivatives possessing a taurine amide residue from a marine sponge of the family Spongiidae

Two new acetylenic fatty acid derivatives possessing a taurine amide residue, taurospongins B (1) and C (2), have been isolated from an Okinawan marine sponge of the family Spongiidae.

Total synthesis and biological evaluation of (+)-gambieric acid A and its analogues

In this study, we report the first total synthesis and complete stereostructure of gambieric acid A, a potent antifungal polycyclic ether metabolite, in detail. The A/B-ring exocyclic enol ether 32 was prepared through a Suzuki-Miyaura coupling of the B-ring vinyl iodide 18 and the alkylborate 33 and subsequent closure of the A-ring by using diastereoselective bromoetherification as the key transformation. Suzuki-Miyaura coupling of 32 with acetate-derived enol phosphate 49, followed by ring-closing metathesis of the derived diene, produced the D-ring. Subsequent closure of the C-ring through a mixed thioacetalization completed the synthesis of the A/BCD-ring fragment 8. The A/BCD- and F'GHIJ-ring fragments (i.e., 8 and 9) were assembled through Suzuki-Miyaura coupling. The C25 stereogenic center was elaborated by exploiting the intrinsic conformational property of the seven-membered F'-ring. After the oxidative cleavage of the F'-ring, the E-ring was formed as a cyclic mixed thioacetal (i.e., 70) and then stereoselectively allylated by using glycosylation chemistry. Ring-closing metathesis of the diene 3 thus obtained closed the F-ring and completed the polycyclic ether skeleton. Finally, the J-ring side chain was introduced by using a Julia-Kocienski olefination in the presence of CeCl3 to complete the total synthesis of gambieric acid A (1), thereby unambiguously establishing its complete stereostructure. The present total synthesis enabled us to evaluate the antifungal and antiproliferative activities of 1 and several synthetic analogues.

Total synthesis and complete stereostructure of gambieric acid A

Total synthesis of gambieric acid A, a potent antifungal polycyclic ether metabolite, has been accomplished for the first time, which firmly established the complete stereostructure of this natural product.

Prenylated acylphloroglucinols, chipericumins A-D, from Hypericum chinense

Two new tetracyclic prenylated acylphloroglucinols, chipericumins A (1) and B (2), were isolated from the roots of Hypericum chinense, together with two new tricyclic prenylated acylphloroglucinols, chipericumins C (3) and D (4). Their structures were elucidated by spectroscopic data. Chipericumins A-D (1-4) are prenylated acylphloroglucinols having a spiro skeleton with an acyl group, a methyl group, a C(5) unit, and a monoterpene moiety in common.

Studies toward the total synthesis of gambieric acids: stereocontrolled synthesis of a DEFG-ring model compound

A stereocontrolled convergent synthesis of a DEFG-ring model compound of gambieric acids, highly potent antifungal marine polycyclic ether natural products, has been achieved based on Suzuki-Miyaura coupling. Conformational analysis of the model compound revealed that the nine-membered F-ring exists exclusively as a single stable conformer, as opposed to that of ciguatoxins.

Update on methodologies available for ciguatoxin determination: perspectives to confront the onset of ciguatera fish poisoning in Europe

Ciguatera fish poisoning (CFP) occurs mainly when humans ingest finfish contaminated with ciguatoxins (CTXs). The complexity and variability of such toxins have made it difficult to develop reliable methods to routinely monitor CFP with specificity and sensitivity. This review aims to describe the methodologies available for CTX detection, including those based on the toxicological, biochemical, chemical, and pharmaceutical properties of CTXs. Selecting any of these methodological approaches for routine monitoring of ciguatera may be dependent upon the applicability of the method. However, identifying a reference validation method for CTXs is a critical and urgent issue, and is dependent upon the availability of certified CTX standards and the coordinated action of laboratories. Reports of CFP cases in European hospitals have been described in several countries, and are mostly due to travel to CFP endemic areas. Additionally, the recent detection of the CTX-producing tropical genus Gambierdiscus in the eastern Atlantic Ocean of the northern hemisphere and in the Mediterranean Sea, as well as the confirmation of CFP in the Canary Islands and possibly in Madeira, constitute other reasons to study the onset of CFP in Europe [1]. The question of the possible contribution of climate change to the distribution of toxin-producing microalgae and ciguateric fish is raised. The impact of ciguatera onset on European Union (EU) policies will be discussed with respect to EU regulations on marine toxins in seafood. Critical analysis and availability of methodologies for CTX determination is required for a rapid response to suspected CFP cases and to conduct sound CFP risk analysis.

Synthesis of marine polycyclic polyethers via endo-selective epoxide-opening cascades

The proposed biosynthetic pathways to ladder polyethers of polyketide origin and oxasqualenoids of terpenoid origin share a dramatic epoxide-opening cascade as a key step. Polycyclic structures generated in these biosynthetic pathways display biological effects ranging from potentially therapeutic properties to extreme lethality. Much of the structural complexity of ladder polyether and oxasqualenoid natural products can be traced to these hypothesized cascades. In this review we summarize how such epoxide-opening cascade reactions have been used in the synthesis of ladder polyethers and oxasqualenoid natural products.

Synthetic studies on gambieric acids, potent antifungal polycyclic ether natural products: reassignment of the absolute configuration of the nonacyclic polyether core by NMR analysis of model compounds

A highly stereocontrolled, convergent synthesis of the A/B-ring fragment of gambieric acids (GAs) has been developed on the basis of (i) a Suzuki-Miyaura coupling of the C1-C6 alkylborate and the C7-C17 vinyl iodide and (ii) a diastereoselective haloetherification for the construction of the A-ring tetrahydrofuran as key steps. Inspection of the (1)H and (13)C NMR chemical shifts of the synthesized A/B-ring model compounds led to a stereochemical reassignment of the absolute configuration of the polycyclic ether core of GAs. This structure revision was further supported by a synthesis of the A/BC-ring model compound of gambieric acid B and a comparison of its (1)H and (13)C NMR data with those of the natural product.

Bromopyrrole alkaloids from marine sponges of the genus Agelas

Four new bromopyrrole alkaloids, nagelamides O (1) and P (2) and mukanadins E (3) and F (4), were isolated from three collections of Okinawan marine sponges of the genus Agelas. The structures and stereochemistry of 1-4 were elucidated on the basis of their spectroscopic data.

Stereocontrolled synthesis of the A/B-ring fragment of gambieric acid B: reassignment of the absolute configuration of the polycyclic ether region

Stereocontrolled synthesis of the A/B-ring fragment of the originally assigned structure of gambieric acid B and its possible diastereomers has been accomplished. Detailed comparison of their 1H and 13C NMR data with those of the corresponding moiety of the natural product culminated in a stereochemical reassignment of the absolute configuration of the polycyclic ether region of gambieric acid B.

Convergent strategies for the total synthesis of polycyclic ether marine metabolites

Marine polycyclic ether natural products continue to fascinate chemists and biologists due to their exceptionally large and complex molecular architectures and potent and diverse biological activities. Tremendous progress has been made over the past decade toward the total synthesis of marine polycyclic ether natural products. In this area, a convergent strategy for assembling small fragments into an entire molecule always plays a key role in successful total synthesis. This review describes our efforts to develop convergent strategies for the synthesis of polycyclic ethers and their application to the total synthesis of gambierol, gymnocin-A, and brevenal, and to the partial synthesis of the central part of ciguatoxins and the nonacyclic polyether skeleton of gambieric acids.

Synthesis of an A-E gambieric acid subunit with use of a C-glycoside centered strategy

This paper describes our synthesis of the A-E subunit of gambieric acid (GA) in addition to the synthesis of the A-ring and the C-E tricycle. The use of an enol ether-olefin RCM strategy to couple the A and C-E subunits and, in the process, generate the B-ring is noteworthy.

Biotechnological significance of toxic marine dinoflagellates

Dinoflagellates are microalgae that are associated with the production of many marine toxins. These toxins poison fish, other wildlife and humans. Dinoflagellate-associated human poisonings include paralytic shellfish poisoning, diarrhetic shellfish poisoning, neurotoxic shellfish poisoning, and ciguatera fish poisoning. Dinoflagellate toxins and bioactives are of increasing interest because of their commercial impact, influence on safety of seafood, and potential medical and other applications. This review discusses biotechnological methods of identifying toxic dinoflagellates and detecting their toxins. Potential applications of the toxins are discussed. A lack of sufficient quantities of toxins for investigational purposes remains a significant limitation. Producing quantities of dinoflagellate bioactives requires an ability to mass culture them. Considerations relating to bioreactor culture of generally fragile and slow-growing dinoflagellates are discussed. Production and processing of dinoflagellates to extract bioactives, require attention to biosafety considerations as outlined in this review.

Total Synthesis of Gambierol: The Generation of the A–C and F–H Subunits by Using a C-Glycoside Centered Strategy

Gambierol, a representative of the marine ladder toxin family, consists of eight ether rings, 18 stereocenters, and two challenging pyranyl rings having methyl groups that are in a 1,3-diaxial orientation to one another. Herein we describe the generation of gambierol's A-C and F-H ring systems and demonstrate the versatility of the glycosyl anhydride, enol ether-olefin RCM strategy to fused polycyclic ethers. This work has both enabled us to generate sufficient quantities of the gambierol precursors and has enabled us to better understand the chemical transformations that were key to these efforts. Fundamental work included efforts to C-glycosides and C-ketosides, Claisen rearrangements, and enol ether-olefin RCM reactions.