Acetate labeling patterns of dinoflagellate polyketides, amphidinols 2, 3 and 4

Investigating A Multi-Domain Polyketide Synthase in Amphidinium carterae

Dinoflagellates are unicellular organisms that are implicated in harmful algal blooms (HABs) caused by potent toxins that are produced through polyketide synthase (PKS) pathways. However, the exact mechanisms of toxin synthesis are unknown due to a lack of genomic segregation of fat, toxins, and other PKS-based pathways. To better understand the underlying mechanisms, the actions and expression of the PKS proteins were investigated using the toxic dinoflagellate Amphidinium carterae as a model. Cerulenin, a known ketosynthase inhibitor, was shown to reduce acetate incorporation into all fat classes with the toxins amphidinol and sulpho-amphidinol. The mass spectrometry analysis of cerulenin-reacted synthetic peptides derived from ketosynthase domains of A. carterae multimodular PKS transcripts demonstrated a strong covalent bond that could be localized using collision-induced dissociation. One multi-modular PKS sequence present in all dinoflagellates surveyed to date was found to lack an AT domain in toxin-producing species, indicating trans-acting domains, and was shown by Western blotting to be post-transcriptionally processed. These results demonstrate how toxin synthesis in dinoflagellates can be differentiated from fat synthesis despite common underlying pathway.

A Comparison of Dinoflagellate Thiolation Domain Binding Proteins Using In Vitro and Molecular Methods

Dinoflagellates play important roles in ecosystems as primary producers and consumers making natural products that can benefit or harm environmental and human health but are also potential therapeutics with unique chemistries. Annotations of dinoflagellate genes have been hampered by large genomes with many gene copies that reduce the reliability of transcriptomics, quantitative PCR, and targeted knockouts. This study aimed to functionally characterize dinoflagellate proteins by testing their interactions through in vitro assays. Specifically, nine Amphidinium carterae thiolation domains that scaffold natural product synthesis were substituted into an indigoidine synthesizing gene from the bacterium Streptomyces lavendulae and exposed to three A. carterae phosphopantetheinyl transferases that activate synthesis. Unsurprisingly, several of the dinoflagellate versions inhibited the ability to synthesize indigoidine despite being successfully phosphopantetheinated. However, all the transferases were able to phosphopantetheinate all the thiolation domains nearly equally, defying the canon that transferases participate in segregated processes via binding specificity. Moreover, two of the transferases were expressed during growth in alternating patterns while the final transferase was only observed as a breakdown product common to all three. The broad substrate recognition and compensatory expression shown here help explain why phosphopantetheinyl transferases are lost throughout dinoflagellate evolution without a loss in a biochemical process.

Discovery of benthol A and its challenging stereochemical assignment: opening up a new window for skeletal diversity of super-carbon-chain compounds

Super-carbon-chain compounds (SCCCs) are marine organic molecules featuring long polyol carbon chains with numerous stereocenters. Polyol-polyene compounds (PPCs) and ladder-frame polyethers (LFPs) are two major families. It is highly challenging to establish the absolute configurations of SCCCs. In this century, few new SCCC families have been reported. Benthol A, an aberrant SCCC, was obtained from a South China Sea benthic dinoflagellate that should belong to a new taxon. Its planar structure and absolute configuration, containing thirty-five carbon stereocenters, were unambiguously established by a combination of extensive NMR spectroscopic investigations, periodate degradation of the 1,2-diol groups, ozonolysis of the carbon-carbon double bonds, J-based configurational analysis, NOE interactions, modified Mosher's MTPA ester method, and DFT-NMR ¹³C chemical-shift calculations aided by DP4+ statistical analysis. Benthol A displayed potent antimalarial activity against Plasmodium falciparum 3D7 parasites. This new molecule combines extraordinary structural features, particularly eight scattered ether rings on a C₇₂ backbone chain, which places it within a new SCCC family between PPCs and LFPs, herein termed polyol-polyether compounds. This suggestion was strongly supported by principal component analysis. The discovery of benthol A does not only provide new insights into the untapped biosynthetic potential of marine dinoflagellates, but also opens up a new window for skeletal diversity of SCCCs.

A Global Approach to Estimating the Abundance and Duplication of Polyketide Synthase Domains in Dinoflagellates

Many dinoflagellate species make toxins in a myriad of different molecular configurations but the underlying chemistry in all cases is presumably via modular synthases, primarily polyketide synthases. In many organisms modular synthases occur as discrete synthetic genes or domains within a gene that act in coordination thus forming a module that produces a particular fragment of a natural product. The modules usually occur in tandem as gene clusters with a syntenic arrangement that is often predictive of the resultant structure. Dinoflagellate genomes however are notoriously complex with individual genes present in many tandem repeats and very few synthetic modules occurring as gene clusters, unlike what has been seen in bacteria and fungi. However, modular synthesis in all organisms requires a free thiol group that acts as a carrier for sequential synthesis called a thiolation domain. We scanned 47 dinoflagellate transcriptomes for 23 modular synthase domain models and compared their abundance among 10 orders of dinoflagellates as well as their co-occurrence with thiolation domains. The total count of domain types was quite large with over thirty-thousand identified, 29 000 of which were in the core dinoflagellates. Although there were no specific trends in domain abundance associated with types of toxins, there were readily observable lineage specific differences. The Gymnodiniales, makers of long polyketide toxins such as brevetoxin and karlotoxin had a high relative abundance of thiolation domains as well as multiple thiolation domains within a single transcript. Orders such as the Gonyaulacales, makers of small polyketides such as spirolides, had fewer thiolation domains but a relative increase in the number of acyl transferases. Unique to the core dinoflagellates, however, were thiolation domains occurring alongside tetratricopeptide repeats that facilitate protein-protein interactions, especially hexa and hepta-repeats, that may explain the scaffolding required for synthetic complexes capable of making large toxins. Clustering analysis for each type of domain was also used to discern possible origins of duplication for the multitude of single domain transcripts. Single domain transcripts frequently clustered with synonymous domains from multi-domain transcripts such as the BurA and ZmaK like genes as well as the multi-ketosynthase genes, sometimes with a large degree of apparent gene duplication, while fatty acid synthesis genes formed distinct clusters. Surprisingly the acyl-transferases and ketoreductases involved in fatty acid synthesis (FabD and FabG, respectively) were found in very large clusters indicating an unprecedented degree of gene duplication for these genes. These results demonstrate a complex evolutionary history of core dinoflagellate modular synthases with domain specific duplications throughout the lineage as well as clues to how large protein complexes can be assembled to synthesize the largest natural products known.

A Water-Soluble 5/14-Carbobicyclic Steroid with a trans-9,11-Epoxy Ring from the Marine Dinoflagellate Amphidinium gibbosum: Insights into Late-Stage Diversification of Steroids

Gibbosterol A (1), a water-soluble 14-membered carbocyclic steroid with a twisted trans-9,11-epoxy ring, was discovered from the South China Sea dinoflagellate, Amphidinium gibbosum, together with its acid-induced cyclization product 2. It exhibits marked agonistic effects against human pregnane-X-receptor in a dose-dependent manner within the concentration range of 100 nM to 10 μM. Its 5/14-carbobicyclic nucleus is proposed to be originated from late-stage oxidative cleavage of the C5-C10 and C8-C9 bonds of β-sitosterol.

LC-MS/MS Method Development for the Discovery and Identification of Amphidinols Produced by Amphidinium

Amphidinols are polyketides produced by dinoflagellates suspected of causing fish kills. Here, we demonstrate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the identification and quantification of amphidinols (AM). Novel AM were detected by neutral loss (NL) scan and then quantified together with known AM by selection reaction monitoring (SRM). With the new method, AM were detected in four of eight analyzed strains with a maximum of 3680 fg toxin content per cell. In total, sixteen novel AM were detected by NL scan and characterized via their fragmentation patterns. Of these, two substances are glycosylated forms. This is the first detection of glycosylated AM.

Research Progress in the Biosynthetic Mechanisms of Marine Polyether Toxins

Marine polyether toxins, mainly produced by marine dinoflagellates, are novel, complex, and diverse natural products with extensive toxicological and pharmacological effects. Owing to their harmful effects during outbreaks of marine red tides, as well as their potential value for the development of new drugs, marine polyether toxins have been extensively studied, in terms of toxicology, pharmacology, detection, and analysis, structural identification, as well as their biosynthetic mechanisms. Although the biosynthetic mechanisms of marine polyether toxins are still unclear, certain progress has been made. In this review, research progress and current knowledge on the biosynthetic mechanisms of polyether toxins are summarized, including the mechanisms of carbon skeleton deletion, pendant alkylation, and polyether ring formation, along with providing a summary of mined biosynthesis-related genes. Finally, future research directions and applications of marine polyether toxins are discussed.

HPLC-HRMS Quantification of the Ichthyotoxin Karmitoxin from Karlodinium armiger

Being able to quantify ichthyotoxic metabolites from microalgae allows for the determination of ecologically-relevant concentrations that can be simulated in laboratory experiments, as well as to investigate bioaccumulation and degradation. Here, the ichthyotoxin karmitoxin, produced by Karlodinium armiger, was quantified in laboratory-grown cultures using high-performance liquid chromatography (HPLC) coupled to electrospray ionisation high-resolution time-of-flight mass spectrometry (HRMS). Prior to the quantification of karmitoxin, a standard of karmitoxin was purified from K. armiger cultures (80 L). The standard was quantified by fluorescent derivatisation using Waters AccQ-Fluor reagent and derivatised fumonisin B₁ and fumonisin B₂ as standards, as each contain a primary amine. Various sample preparation methods for whole culture samples were assessed, including six different solid phase extraction substrates. During analysis of culture samples, MS source conditions were monitored with chloramphenicol and valinomycin as external standards over prolonged injection sequences (>12 h) and karmitoxin concentrations were determined using the response factor of a closely eluting iturin A2 internal standard. Using this method the limit of quantification was 0.11 μg·mL^-1, and the limit of detection was found to be 0.03 μg·mL^-1. Matrix effects were determined with the use of K. armiger cultures grown with ¹³C-labelled bicarbonate as the primary carbon source.

The Missing Piece in Biosynthesis of Amphidinols: First Evidence of Glycolate as a Starter Unit in New Polyketides from Amphidinium carterae

Two new members of the amphidinol family, amphidinol A (1) and its 7-sulfate derivative amphidinol B (2), were isolated from a strain of Amphidinium carterae of Lake Fusaro, near Naples (Italy), and chemically identified by spectroscopic and spectrometric methods. Amphidinol A showed antifungal activity against Candida albicans (MIC = 19 µg/mL). Biosynthetic experiments with stable isotope-labelled acetate allowed defining the elongation process in 1. For the first time the use of glycolate as a starter unit in the polyketide biosynthesis of amphidinol metabolites was unambiguously demonstrated.

Karmitoxin: An Amine-Containing Polyhydroxy-Polyene Toxin from the Marine Dinoflagellate Karlodinium armiger

Marine algae from the genus Karlodinium are known to be involved in fish-killing events worldwide. Here we report for the first time the chemistry and bioactivity of a natural product from the newly described mixotrophic dinoflagellate Karlodinium armiger. Our work describes the isolation and structural characterization of a new polyhydroxy-polyene named karmitoxin. The structure elucidation work was facilitated by use of 13C enrichment and high-field 2D NMR spectroscopy, where 1H-13C long-range correlations turned out to be very informative. Karmitoxin is structurally related to amphidinols and karlotoxins; however it differs by containing the longest carbon-carbon backbone discovered for this class of compounds, as well as a primary amino group. Karmitoxin showed potent nanomolar cytotoxic activity in an RTgill-W1 cell assay as well as rapid immobilization and eventual mortality of the copepod Acartia tonsa, a natural grazer of K. armiger.

Transcriptome Analysis of Core Dinoflagellates Reveals a Universal Bias towards "GC" Rich Codons

Although dinoflagellates are a potential source of pharmaceuticals and natural products, the mechanisms for regulating and producing these compounds are largely unknown because of extensive post-transcriptional control of gene expression. One well-documented mechanism for controlling gene expression during translation is codon bias, whereby specific codons slow or even terminate protein synthesis. Approximately 10,000 annotatable genes from fifteen “core” dinoflagellate transcriptomes along a range of overall guanine and cytosine (GC) content were used for codonW analysis to determine the relative synonymous codon usage (RSCU) and the GC content at each codon position. GC bias in the analyzed dataset and at the third codon position varied from 51% and 54% to 66% and 88%, respectively. Codons poor in GC were observed to be universally absent, but bias was most pronounced for codons ending in uracil followed by adenine (UA). GC bias at the third codon position was able to explain low abundance codons as well as the low effective number of codons. Thus, we propose that a bias towards codons rich in GC bases is a universal feature of core dinoflagellates, possibly relating to their unique chromosome structure, and not likely a major mechanism for controlling gene expression.

Biosynthetic Studies of 13-Desmethylspirolide C Produced by Alexandrium ostenfeldii (= A. peruvianum): Rationalization of the Biosynthetic Pathway Following Incorporation of (13)C-Labeled Methionine and Application of the Odd-Even Rule of Methylation

Understanding the biosynthesis of dinoflagellate polyketides presents many unique challenges. Because of the remaining hurdles to dinoflagellate genome sequencing, precursor labeling studies remain the only viable way to investigate dinoflagellate biosynthesis. However, prior studies have shown that polyketide chain assembly does not follow any of the established processes. Additionally, acetate, the common precursor for polyketides, is frequently scrambled, thus compromising interpretation. These factors are further compounded by low production yields of the compounds of interest. A recent report on the biosynthesis of spirolides, a group belonging to the growing class of toxic spiroimines, provided some insight into the polyketide assembly process based on acetate labeling studies, but many details were left uncertain. By feeding (13)C methyl-labeled methionine to cultures of Alexandrium ostenfeldii, the producing organism of 13-desmethylspirolide C, and application of the odd-even methylation rule, the complete biosynthetic pathway has been established.

The cytotoxic mechanism of karlotoxin 2 (KmTx 2) from Karlodinium veneficum (Dinophyceae)

This study demonstrates that the polyketide toxin karlotoxin 2 (KmTx 2) produced by Karlodinium veneficum, a dinoflagellate associated with fish kills in temperate estuaries world-wide, alters vertebrate cell membrane permeability. Microfluorimetric and electrophysiological measurements were used to determine that vertebrate cellular toxicity occurs through non-selective permeabilization of plasma membranes, leading to osmotic cell lysis. Previous studies showed that KmTx 2 is lethal to fish at naturally-occurring concentrations measured during fish kills, while sub-lethal doses severely damage gill epithelia. This study provides a mechanistic explanation for the association between K. veneficum blooms and fish kills that has long been observed in temperate estuaries worldwide.

Amphirionin-4 with potent proliferation-promoting activity on bone marrow stromal cells from a marine dinoflagellate amphidinium species

A linear polyketide, amphirionin-4 (1), has been isolated from cultivated algal cells of the marine dinoflagellate Amphidinium species. The structure was elucidated on the basis of detailed analyses of 1D and 2D NMR data, and the absolute configurations of C-4 and C-8 were determined using the modified Mosher's method. Amphirionin-4 (1) exhibited extremely potent proliferation-promoting activity on murine bone marrow stromal ST-2 cells (950% promotion) at a concentration of 0.1 ng/mL.

Antifungal amphidinol 18 and its 7-sulfate derivative from the marine dinoflagellate Amphidinium carterae

Two new polyketides of the amphidinol family, amphidinol 18 (AM18, 1) and its corresponding 7-sulfate derivative (AM19, 2), have been isolated from the MeOH extract of the dinoflagellate Amphidinium carterae. Structure elucidation of the two polyoxygenated molecules has been accomplished by extensive use of spectroscopic and spectrometric techniques. AM18 exhibited antifungal activity against Candida albicans at 9 μg/mL.

Structure and relative potency of several karlotoxins from Karlodinium veneficum

The karlotoxins are a family of amphidinol-like compounds that play roles in avoiding predation and in prey capture for the toxic dinoflagellate Karlodinium veneficum. The first member of the toxin group to be reported was KmTx 1 (1), and here we report an additional five new members of this family (3-7) from the same strain. Of these additional compounds, KmTx 3 (3) differs from KmTx 1 (1) in having one less methylene group in the saturated portion of its lipophilic arm. In addition, 64-E-chloro-KmTx 3 (4) and 10-O-sulfo-KmTx 3 (5) were identified. Likewise, 65-E-chloro-KmTx 1 (6) and 10-O-sulfo-KmTx 1 (7) were also isolated. Comparison of the hemolytic activities of the newly isolated compounds to that of KmTx 1 shows that potency correlates positively with the length of the lipophilic arm and is disrupted by sulfonation of the polyol arm.

Structure and biosynthesis of amphidinol 17, a hemolytic compound from Amphidinium carterae

Amphidinol 17 (AM17; 1), a novel amphidinol, has been isolated from a Bahamas strain of Amphidinium carterae. This new congener contains the signature hairpin region and a Delta(6) polyene arm, whereas the polyol arm is distinct from those of other amphidinols. The pattern of acetate incorporation in 1 was directly determined by feeding a single labeled substrate, [2-(13)C]acetate. While the highly conserved regions within the amphidinol family of AM17 have exhibited identical occurrences of cleaved acetates to other amphidinols for which the biosynthesis has been explored, the polyol arm for AM17 displays a higher degree of nascent chain processing that shows similarities to amphidinolide biosynthesis. AM17 exhibited an EC(50) of 4.9 microM in a hemolytic assay using human red blood cells but displayed no detectable antifungal activity.

Toxic dinoflagellates (Dinophyceae) from Rarotonga, Cook Islands

Dinoflagellate species isolated from the green calcareous seaweed, Halimeda sp. J.V. Lamouroux, growing in Rarotongan lagoons, included Gambierdiscus australes Faust & Chinain, Coolia monotis Meunier, Amphidinium carterae Hulburth, Prorocentrum lima (Ehrenberg) Dodge, P. cf. maculosum Faust and species in the genus Ostreopsis Schmidt. Isolates were identified to species level by scanning electron microscopy and/or DNA sequence analysis. Culture extracts of G. australes isolate CAWD149 gave a response of 0.04 pg P-CTX-1 equiv. per cell by an N2A cytotoxicity assay (equivalent to ca 0.4 pg CTX-3C cell(-1)). However, ciguatoxins were not detected by LC-MS/MS. Partitioned fractions of the cell extracts potentially containing maitotoxin were found to be very toxic to mice after intraperitoneal (i.p.) injection. A. carterae was also of interest as extracts of mass cultures caused respiratory paralysis in mice at high doses, both by i.p. injection and by oral administration. The Rarotongan isolate fell into a different clade to New Zealand A. carterae isolates, based on DNA sequence analysis, and also had a different toxin profile. As A. carterae co-occurred with G. australes, it may contribute to human poisonings attributed to CTX and warrants further investigation. A crude extract of C. monotis was of low toxicity to mice by i.p. injection, and an extract of Ostreopsis sp. was negative in the palytoxin haemolysis neutralisation assay.

Identification of very-long-chain polyunsaturated fatty acids from Amphidinium carterae by atmospheric pressure chemical ionization liquid chromatography-mass spectroscopy

A method is described for the enrichment of very-long-chain polyunsaturated fatty acids (VLCPUFAs) from total fatty acids of Amphidinium carterae and their identification as picolinyl esters by means of microbore liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization (LC-MS/APCI). The combination of argentation TLC and LC-MS/APCI was used to identify unusual VLCPUFAs up to hexatriacontaoctaenoic acid. Two acids, 36:7n-6 and 36:8n-3, were also synthesized to unambiguously confirm their structure. The possibilities of VLCPUFAs biosynthesis are proposed.

Roles of integral protein in membrane permeabilization by amphidinols

Amphidinols (AMs) are a group of dinoflagellate metabolites with potent antifungal activity. As is the case with polyene macrolide antibiotics, the mode of action of AMs is accounted for by direct interaction with lipid bilayers, which leads to formation of pores or lesions in biomembranes. However, it was revealed that AMs induce hemolysis with significantly lower concentrations than those necessary to permeabilize artificial liposomes, suggesting that a certain factor(s) in erythrocyte membrane potentiates AM activity. Glycophorin A (GpA), a major erythrocyte protein, was chosen as a model protein to investigate interaction between peptides and AMs such as AM2, AM3 and AM6 by using SDS-PAGE, surface plasmon resonance, and fluorescent-dye leakages from GpA-reconstituted liposomes. The results unambiguously demonstrated that AMs have an affinity to the transmembrane domain of GpA, and their membrane-permeabilizing activity is significantly potentiated by GpA. Surface plasmon resonance experiments revealed that their interaction has a dissociation constant of the order of 10 microM, which is significantly larger than efficacious concentrations of hemolysis by AMs. These results imply that the potentiation action by GpA or membrane integral peptides may be due to a higher affinity of AMs to protein-containing membranes than that to pure lipid bilayers.

Synthesis of the C1-C52 fragment of amphidinol 3, featuring a beta-alkoxy alkyllithium addition reaction

An advanced intermediate for the synthesis of amphidinol 3 has been prepared. A cross-metathesis reaction was used to couple the C1-C12 and C13-C26 segments. An unusual beta-alkoxy alkyllithium reagent was generated from this segment and added to a Weinreb amide to assemble the C1-C52 section of amphidinol 3. These compounds represent some of the most advanced intermediates reported to date for the synthesis of amphidinol 3.

Development of an access route to the c31-c52 central core of amphidinol 3

[reaction: see text] An asymmetric synthesis of the heavily oxygenated inner sector of amphidinol 3 constituted of C31-C52 is described. The successful pathway highlights construction of the pair of identical tetrahydropyran subunits from a common intermediate.

Bioactive macrolides and polyketides from marine dinoflagellates of the genus Amphidinium

Marine microorganisms such as bacteria, cyanobacteria, dinoflagellates, and others have attracted many natural product chemists as the real producers of marine toxins such as fish and algal poisons as well as bioactive substances isolated from marine invertebrates such as sponges and tunicates. Among marine microorganisms, dinoflagellates have proved to be important sources of marine toxins and have been investigated worldwide by natural product chemists. We have continued investigations on chemically interesting and biologically significant secondary metabolites from Amphidinium spp., of a genus of symbiotic marine dinoflagellates separated from inside cells of Okinawan marine flatworms. This review covers the results described in our recent publications on a series of cytotoxic macrolides, designated amphidinolides, and long-chain polyketides isolated from Amphidinium spp. In this review, topics include the isolation, structure elucidation, synthesis, biosynthesis, and bioactivity of amphidinolides and long-chain polyketides.

Cryopreservation of economically valuable marine micro-algae in the classes Bacillariophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Haptophyceae, Prasinophyceae, and Rhodophyceae

The ability to routinely cryopreserve micro-algal species reduces costs associated with maintaining large culture collections and reduces the risks of losing particular strains or species through contamination and genetic drift. Cryopreservation is also a useful adjunct in aquaculture hatcheries for strains of micro-algae where the nutritional status may change as a result of continuous sub-culture. In this study, cryopreservation of isolates from seven micro-algal classes was investigated. Successful candidates included the marine dinoflagellates Amphidinium carterae, Amphidinium trulla, and Gymnodinium simplex, and the haptophytes Chrysochromulina simplex, Prymnesium parvum, Prymnesium parvum f. patelliferum, Isochrysis galbana, and Pavlova lutheri. Also successfully cryopreserved were the planktonic diatoms Chaetoceros calcitrans, Chaetoceros muelleri, Chaetoceros sp., and the benthic Nitzschia ovalis, the chlorophyte Chlamydomonas coccoides, the rhodophyte Porphyridium purpureum, the prasinophytes Tetraselmis chuii, and Tetraselmis suecica, and the cyanophytes Raphidiopsis sp., and Aphanizomenon flos-aquae. All species were successfully cryopreserved using 15% Me2SO.

The polyol domain of amphidinol 3. A stereoselective synthesis of the entire C(1)-C(30) sector

[structure: see text] The richly oxygenated C(1)-C(30) polyol segment of amphidinol 3 has been synthesized in protected form. Incorporated in this long chain are 10 of the 25 stereogenic centers housed in the target. The asymmetric pathway that has been developed is based on the efficient union of three independently prepared subunits.

A C-glycosidation approach to the central core of amphidinol 3: synthesis of the c39-c52 fragment

[reaction: see text] A concise route to an advance precursor (3) of the central core of amphidinol 3, a natural occurring polyketide, has been developed by applying a reductive lithiation as key step. The origin of the diastereoselectivity of this reaction was comprehensively studied for nucleophilic C-glycoside donor 5 and differently protected analogues.

Synthesis of the C(1)-C(25) fragment of amphidinol 3: application of the double-allylboration reaction for synthesis of 1,5-diols

[structure: see text] A synthesis of the C(1)-C(25) fragment of amphidinol 3 is described. The synthesis features two applications of double allylboration reaction methodology for the highly stereoselective synthesis of 1,5-diol units in the C(1)-C(15) segment.

The biosynthesis, molecular genetics and enzymology of the polyketide-derived metabolites

This review covers the biosynthesis of aliphatic and aromatic polyketides as well as mixed polyketide/NRPS metabolites, and discusses the molecular genetics and enzymology of the proteins responsible for their formation.

Prorocentin, a New Polyketide from the Marine Dinoflagellate Prorocentrum lima

Prorocentin (1), isolated from an okadaic acid-producing organism, Prorocentrum lima, possessed all-trans trienes, an epoxide, as well as the 6/6/6-trans-fused/spiro-linked polyether ring moieties. The unique structure supports the proposed cyclization mechanism, polyene formation, epoxidation, and cyclization, of marine polyether toxins. The relative stereostructure was determined on the basis of spectral data. [structure: see text]

Membrane-permeabilizing activities of amphidinol 3, polyene-polyhydroxy antifungal from a marine dinoflagellate

Amphidinols, which are polyene-polyhydroxy metabolites produced by the marine dinoflagellate Amphidinium klebsii, possess potent antifungal and hemolytic activities. The membrane permeabilizing actions of amphidinol 3, the most potent homologue, were compared with those of polyene antibiotics, amphotericin B (AmB) and filipin, in hemolytic tests, 23Na nuclear magnetic resonance (NMR)-based membrane permeabilizing assays, and UV spectroscopy for liposome-bound forms. In Na+ flux experiments using large unilamellar vesicles (LUVs), ion efflux by amphidinol 3 was inhibited by cholesterol or ergosterol, which was opposed to previous results [J. Mar. Biotechnol., 5 (1997) 124]. When the effect of the agents on the size of vesicles was examined by light scattering experiments, amphidinol 3 did not significantly alter their size while filipin and synthetic detergent Triton X-100 did. The observations implied that the activity of amphidinol 3 was mainly due to formation of large pores/lesions in liposomes rather than detergent-like disruption of membrane. The pore/lesion size was estimated to be 2.0-2.9 nm in diameter on the basis of osmotic protection experiments using blood cells. The UV spectra in liposomes, which revealed the close interaction of polyene moieties in a lipid bilayer, further implied that the membrane activity of amphidinol 3 is caused by the molecular assemblage formed in biomembrane. These results disclose that amphidinol 3 is one of few non-ionic compounds that possess potent membrane permeabilizing activity with non-detergent mechanism.