Academic literature on the topic 'Pectenotoxins'

Pectenotoxins (PTXs) are produced by Dinophysis spp., along with okadaic acid, dinophysistoxin 1, and dinophysistoxin 2. The okadaic acid group toxins cause diarrhetic shellfish poisoning (DSP), so are therefore regulated. New Zealand currently includes pectenotoxins within the DSP regulations. To determine the impact of this decision, shellfish biotoxin data collected between 2009 and 2019 were examined. They showed that 85 samples exceeded the DSP regulatory limit (0.45%) and that excluding pectenotoxins would have reduced this by 10% to 76 samples. The incidence (1.3%) and maximum concentrations of pectenotoxins (0.079 mg/kg) were also found to be low, well below the current European Food Safety Authority (EFSA) safe limit of 0.12 mg/kg. Inclusion within the DSP regulations is scientifically flawed, as pectenotoxins and okadaic acid have a different mechanism of action, meaning that their toxicities are not additive, which is the fundamental principle of grouping toxins. Furthermore, evaluation of the available toxicity data suggests that pectenotoxins have very low oral toxicity, with recent studies showing no oral toxicity in mice dosed with the PTX analogue PTX2 at 5000 µg/kg. No known human illnesses have been reported due to exposure to pectenotoxins in shellfish, a fact which combined with the toxicity data indicates that they pose negligible risk to humans. Regulatory policies should be commensurate with the level of risk, thus deregulation of PTXs ought to be considered, a stance already adopted by some countries.

Several planktonic dinoflagellate species of the genus Dinophysis produce one or two groups of lipophilic toxins: (i) okadaic acid (OA) and its derivatives, the dinophysistoxins (DTXs), and (ii) pectenotoxins (PTXs) [...]

Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xviii, 211 p.; also includes graphics Includes bibliographical references (p. 128-134). Available online via OhioLINK's ETD Center

Pectenotoxins (PTXs) are a group of large cyclic polyether compounds associated with diarrhetic shellfish poisoning (DSP) as they are often found in combination with other DSPs such as okadaic acid (OA) and dinophysis toxins (DTXs) in shellfish. Although classified and regulated with the DSPs, there is debate over whether these toxins should be classified with DSP toxins. To date, ten different analogues of PTXs have been identified from shellfish and algae, and of these, the pectenotoxin-2 seco acids (PTX2-SAs) are of particular interest as they have previously been implicated in a shellfish poisoning incident in Australia, but relatively little was known of their toxicology. One such incident occurred in December 1997, when approximately 200 people were reported with severe diarrhoetic shellfish poisoning in Northern New South Wales (NSW). Analysis of the shellfish associated with this incident revealed relatively high PTX2-SA concentrations (approx. 300 micrograms/kg shellfish meat), with only trace amounts of pectenotoxin-2 (PTX2) and OA. Following this incident, PTX2-SAs were considered a health threat and guidelines were implemented in the absence of toxicological data, which has caused a great economic burden to shellfish industries around the globe, in particular to Australia, New Zealand and Ireland. Such regulation created in the absence of scientific data demonstrated the need to determine the toxicology of PTX2-SAs in commercial shellfish. Thus a comprehensive study on the toxicology and possible health implications of the PTX2-SAs in Australian shellfish was conducted. PTX2-SAs were isolated in different batches from shellfish (pipis, oysters and mussels) and from algal bloom samples of Dinophysis caudata. Toxin extraction was conducted with several purification stages and chemical analysis was performed with high-performance liquid chromatography coupled to a tandem mass spectrometer (HPLC-MS/MS). The chemical stability of the PTX2-SAs was investigated to ensure consistency of doses between toxicology experiments. Acute dosing studies with mice were then performed and included toxicopathology investigations with light microscopy and electron microscopy, in addition to toxin distribution studies and investigation of in vivo lipid peroxidation. In vitro studies with HepG2 cells included cytotoxicity assays, cell cycle investigations using flow cytometry and gene expression profiling of cells exposed to PTX2-SAs employing cDNA microarray technology. Acute pathology studies demonstrated that the PTX2-SAs do not cause the characteristic symptoms or lesions associated with DSP toxins. No diarrhoea was observed at any dose level in mice and no deaths occurred up to the maximum dosing level of 1.6mg/kg PTX2-SA. Only one batch of PTX2-SA extract produced toxic lesions characteristic of a DSP toxin (batch 1-pilot study) but after follow up studies, it was determined that this first batch of shellfish most likely contained an additional unidentified shellfish toxin or contaminant that co-extracted with PTX2-SAs during toxin isolation and purification procedures. This finding highlighted the importance of supporting the inclusion of the mice bioassay in procedures for shellfish toxin testing to enable detection of new toxins, and also highlighted the importance of toxin purification for toxicology studies. A significant rise in malondialdehyde excretion was observed within 24 hours of dosing mice, indicating that the PTX2-SAs may cause damage by lipid peroxidation in vivo. In vitro studies showed HepG2 cells to have cell cycle and gene expression changes within 24 hours of a dose of 800ng/mL PTX2-SAs. Cell cycle arrest was observed at the G2/M checkpoint and gene expression changes included alterations in genes involved in cell cycle control, lipid metabolism and transport, lipid genesis and trace metal transport. Many genes involved in DNA repair processes were moderated at the 24 hour point, but as no apoptosis was observed up to 72 hours post dosing it is a promising indication that any DNA damage that may have been caused by the administration of PTX2-SAs was not lethal, and was able to be repaired. In light of the information provided by toxicology investigations in this PhD, with particular reference to evidence of in vivo lipid peroxidation by raised levels of MDA in mouse urine, and changes in cell cycle distribution and gene expression in a cultured human cell line, it is concluded that there is potential for these toxins to induce biological changes in mammalian cells in vivo and in vitro, and hence potential for PTX2-SAs to cause health effects in humans. During the course of this three-year study, developments in techniques for shellfish toxin identification within our laboratories have revealed that the shellfish responsible for the 1997 NSW poisoning incident contained significant concentrations of okadaic acid acyl esters that were not detected at the time of the NSW incident. Although reportedly less toxic than okadaic acid itself, the OA ester concentrations present may have been sufficient to cause the observed symptoms. It is also theorized that these esters could be hydrolyzed in the human gastro-intestinal tract to release okadaic acid. In the light of this new evidence and with no pathology lesions or symptoms of diarrhoea being observed in PTX2-SA dosing studies with mice, we now believe these OA acyl esters to be the causative agent in the 1997 NSW DSP incident and not the PTX2-SAs. Nothing is currently known of the chronic toxicology of PTX2-SAs and thus their potential implications to public health in the long term cannot determined. The toxicology investigations in this thesis were acute studies, and it has not been established if the observed changes could be repaired or returned within normal limits without the manifestation of illness or disease occurring. Utilizing the acute toxicology information in this thesis, a health risk assessment for consumption of PTX2-SA contaminated shellfish was performed. This risk assessment, employing numerous safety factors essential for an incomplete data set, produced guideline values that are lower than the current recommend concentrations. To date, there has been no solid evidence that PTX2-SAs cause illness in humans – all documented incidents involving the PTX2-SAs have also included other DSP contaminants that are known to cause human illness. Pathology has not unequivocally been demonstrated in animal studies and thus, in consideration of the epidemiological evidence, PTX2-SAs cannot be considered as high a risk to public health as was previously thought. For the reasons discussed above, and weighing up risk-benefit considerations of the economic burden the current guideline values are causing to shellfish industries around the globe, it is recommended that levels of PTX2-SAs be monitored in recognition of the precautionary principle, but no longer regulated as tightly with other DSPs until such a time that toxicological or epidemiological evidence can prove that the PTX2-SAs are a DSP and are a more considerable threat to human health than has been indicated by toxicology studies in this thesis. This study has produced a substantial amount of acute toxicology data and has provided a good basis for future chronic toxicology investigations with the PTX2-SAs for regulatory purposes.

Pectenotoxins (PTXs) are a group of large cyclic polyether compounds associated with diarrhetic shellfish poisoning (DSP) as they are often found in combination with other DSPs such as okadaic acid (OA) and dinophysis toxins (DTXs) in shellfish. Although classified and regulated with the DSPs, there is debate over whether these toxins should be classified with DSP toxins. To date, ten different analogues of PTXs have been identified from shellfish and algae, and of these, the pectenotoxin-2 seco acids (PTX2-SAs) are of particular interest as they have previously been implicated in a shellfish poisoning incident in Australia, but relatively little was known of their toxicology. One such incident occurred in December 1997, when approximately 200 people were reported with severe diarrhoetic shellfish poisoning in Northern New South Wales (NSW). Analysis of the shellfish associated with this incident revealed relatively high PTX2-SA concentrations (approx. 300 micrograms/kg shellfish meat), with only trace amounts of pectenotoxin-2 (PTX2) and OA. Following this incident, PTX2-SAs were considered a health threat and guidelines were implemented in the absence of toxicological data, which has caused a great economic burden to shellfish industries around the globe, in particular to Australia, New Zealand and Ireland. Such regulation created in the absence of scientific data demonstrated the need to determine the toxicology of PTX2-SAs in commercial shellfish. Thus a comprehensive study on the toxicology and possible health implications of the PTX2-SAs in Australian shellfish was conducted. PTX2-SAs were isolated in different batches from shellfish (pipis, oysters and mussels) and from algal bloom samples of Dinophysis caudata. Toxin extraction was conducted with several purification stages and chemical analysis was performed with high-performance liquid chromatography coupled to a tandem mass spectrometer (HPLC-MS/MS). The chemical stability of the PTX2-SAs was investigated to ensure consistency of doses between toxicology experiments. Acute dosing studies with mice were then performed and included toxicopathology investigations with light microscopy and electron microscopy, in addition to toxin distribution studies and investigation of in vivo lipid peroxidation. In vitro studies with HepG2 cells included cytotoxicity assays, cell cycle investigations using flow cytometry and gene expression profiling of cells exposed to PTX2-SAs employing cDNA microarray technology. Acute pathology studies demonstrated that the PTX2-SAs do not cause the characteristic symptoms or lesions associated with DSP toxins. No diarrhoea was observed at any dose level in mice and no deaths occurred up to the maximum dosing level of 1.6mg/kg PTX2-SA. Only one batch of PTX2-SA extract produced toxic lesions characteristic of a DSP toxin (batch 1-pilot study) but after follow up studies, it was determined that this first batch of shellfish most likely contained an additional unidentified shellfish toxin or contaminant that co-extracted with PTX2-SAs during toxin isolation and purification procedures. This finding highlighted the importance of supporting the inclusion of the mice bioassay in procedures for shellfish toxin testing to enable detection of new toxins, and also highlighted the importance of toxin purification for toxicology studies. A significant rise in malondialdehyde excretion was observed within 24 hours of dosing mice, indicating that the PTX2-SAs may cause damage by lipid peroxidation in vivo. In vitro studies showed HepG2 cells to have cell cycle and gene expression changes within 24 hours of a dose of 800ng/mL PTX2-SAs. Cell cycle arrest was observed at the G2/M checkpoint and gene expression changes included alterations in genes involved in cell cycle control, lipid metabolism and transport, lipid genesis and trace metal transport. Many genes involved in DNA repair processes were moderated at the 24 hour point, but as no apoptosis was observed up to 72 hours post dosing it is a promising indication that any DNA damage that may have been caused by the administration of PTX2-SAs was not lethal, and was able to be repaired. In light of the information provided by toxicology investigations in this PhD, with particular reference to evidence of in vivo lipid peroxidation by raised levels of MDA in mouse urine, and changes in cell cycle distribution and gene expression in a cultured human cell line, it is concluded that there is potential for these toxins to induce biological changes in mammalian cells in vivo and in vitro, and hence potential for PTX2-SAs to cause health effects in humans. During the course of this three-year study, developments in techniques for shellfish toxin identification within our laboratories have revealed that the shellfish responsible for the 1997 NSW poisoning incident contained significant concentrations of okadaic acid acyl esters that were not detected at the time of the NSW incident. Although reportedly less toxic than okadaic acid itself, the OA ester concentrations present may have been sufficient to cause the observed symptoms. It is also theorized that these esters could be hydrolyzed in the human gastro-intestinal tract to release okadaic acid. In the light of this new evidence and with no pathology lesions or symptoms of diarrhoea being observed in PTX2-SA dosing studies with mice, we now believe these OA acyl esters to be the causative agent in the 1997 NSW DSP incident and not the PTX2-SAs. Nothing is currently known of the chronic toxicology of PTX2-SAs and thus their potential implications to public health in the long term cannot determined. The toxicology investigations in this thesis were acute studies, and it has not been established if the observed changes could be repaired or returned within normal limits without the manifestation of illness or disease occurring. Utilizing the acute toxicology information in this thesis, a health risk assessment for consumption of PTX2-SA contaminated shellfish was performed. This risk assessment, employing numerous safety factors essential for an incomplete data set, produced guideline values that are lower than the current recommend concentrations. To date, there has been no solid evidence that PTX2-SAs cause illness in humans – all documented incidents involving the PTX2-SAs have also included other DSP contaminants that are known to cause human illness. Pathology has not unequivocally been demonstrated in animal studies and thus, in consideration of the epidemiological evidence, PTX2-SAs cannot be considered as high a risk to public health as was previously thought. For the reasons discussed above, and weighing up risk-benefit considerations of the economic burden the current guideline values are causing to shellfish industries around the globe, it is recommended that levels of PTX2-SAs be monitored in recognition of the precautionary principle, but no longer regulated as tightly with other DSPs until such a time that toxicological or epidemiological evidence can prove that the PTX2-SAs are a DSP and are a more considerable threat to human health than has been indicated by toxicology studies in this thesis. This study has produced a substantial amount of acute toxicology data and has provided a good basis for future chronic toxicology investigations with the PTX2-SAs for regulatory purposes.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Public Health
Faculty of Health Sciences
Full Text

This thesis details the application of two synthetic methodologies, developed by the Donohoe group, to the synthesis of the ABC fragment of pectenotoxin-4, a macrolide marine natural product that consists of 19 stereogenic centres, three tetrahydrofuran rings, one spiroketal and one bicyclic ketal embedded within a 26-membered macrocycle. Pivotal to the developed synthetic route was the utilisation of an unprecedented cascade osmium catalysed oxidative cyclisation for the construction of two THF rings (the BC ring system). After successfully developing a model system for the synthesis of the AB anomeric 6,5 spiroketal, which involved the employment of a hydride shift initiated oxo carbenium ion formation followed by intramolecular spiroketalisation, the developed system was then applied to the fully elaborated synthesis of the ABC fragment. The synthesis of the ABC fragment of pectenotoxin-4 was completed in 20 linear steps, with an overall yield of 3.3%.

The EFG-ring system of pectenotoxin-4 was synthesised via a novel pathway which ultilised a cobalt-mediated oxidative cyclisation to access the trans F-ring, and an osmium-mediated oxidative cyclisation to form the cis E-ring. Subsequent union of these fragments, under modified Julia-Kocienski olefination conditions, facilitated the synthesis of the EFG-ring system of pectenotoxin-4. Introduction This chapter reports the previous total syntheses of pectenotoxin molecules, along with completed syntheses of pectenotoxin fragments, including the Donohoe group's synthesis of the ABC-ring system of pectenotoxin-4. Results and Discussion The synthesis of the FG-ring system and subsequent coupling to the E-ring fragment are detailed in this chapter. The final steps from the Julia adduct to the EFG-ring system conclude this chapter.

This thesis details the optimisation and development to the synthesis of the ABC fragment of pectenotoxin-4, a 26-membered macrolide marine natural product bearing 19 stereogenic centres, three tetrahydrofuran rings, one spiroketal and one bicyclic ketal. Introduction This section briefly discusses the isolation, structure elucidation, and biological activity of penctenotoxins, along with a review of previous synthetic efforts on the pectenotoxin family, especially the ABC fragment. It also summarises our group's work in pursuing the total synthesis of this compound. Results and Discussion This section details synthetic efforts to improve the overall yield of the ABC fragment. In particular, it contains the optimisation of a low yield Carreira alkynylation reaction and a revised protecting group strategy to allow orthogonal deprotection on the ABC fragment for further elaborations. The revised route for the ABC fragment of pectenotoxin-4 contains 21 longest linear steps (27 steps in total) from D-mannitol with an overall yield of 2.1% (on average 83% per step).

This thesis explores new synthetic routes for the formation of CDE & EFG fragments of pectenotoxin-4. Chapter 1: Introduction and Previous Work: This chapter reviews the discovery and biological activities of members of the pectenotoxin family. Two previous total syntheses are discussed, and previous work regarding the synthesis of ABC, E and FG fragments within the group is introduced. Chapter 2: Synthesis of the E Ring Fragment of Pectenotoxin-4: The synthesis of the E ring fragment is discussed. Key reactions include Negishi coupling and osmium mediated oxidative cyclisation. Chapter 3: First Generation Strategy for the Synthesis of the D ring: A simple model towards the D ring core was completed using alkyne-epoxide opening strategy. The application on a more sophisticated system was tested. Chapter 4: Second Generation Strategy for the Synthesis of the D ring: Sonogashira coupling was successfully tested as key step to unite two coupling partners; and further functionalisation towards the D ring skeleton was studied. Chapter 5: Third Generation Strategy for the Synthesis of the D ring: The new strategy including a Lewis acid assisted coupling and mercury mediated hydration of alkyne sequence was completed on a simple model. The application on a more sophisticated system was tested. Chapter 6: Synthesis of EFG Fragment of Pectenotoxin-4: Key Julia-Kocienski olefination between E ring fragment and FG ring fragment was examined. The further functionalisation of the resulting coupling product towards EFG fragment was finished. Chapter 7: Experimental: Full experimental procedures and characterisation of compounds are reported.

Thesis (Ph. D.)--Ohio State University, 2002.
Title from first page of PDF file. Document formatted into pages; contains xiv, 242 p.). Includes abstract and vita. Advisor: Leo A. Paquette, Dept. of Chemistry. Includes bibliographical references (p. 233-242).

The cobalt-catalysed oxidative cyclisation of 5-hydroxy alkenes has been demonstrated to be a powerful synthetic tool for the formation of trans-THFs with excellent diastereoselectivity. This thesis describes the utilisation of this methodology in the synthesis of the FG fragment of pectenotoxin-4, allowing the scope of the reaction to be further explored. Introduction: This section introduces the pectenotoxins, a family of structurally complex closed-chain polyether macrolides with promising biological activities. The isolation, structural elucidation, and biological properties of the pectenotoxins are reviewed, along with a summary of previous syntheses towards the FG fragment of pectenotoxin-4. In addition, the cobalt-catalysed oxidative cyclisation of 5-hydroxy alkenes and its application in synthesis is discussed. Results and Discussion: An outline of the synthetic strategy employed in this project and details of the novel retrosynthesis of the C31-C40 fragment of pectenotoxin-4 is described. The synthetic studies carried out towards the synthesis of the FG fragment of pectenotoxin-4 are discussed in detail, with the exploitation of a cobalt-catalysed oxidative cyclisation as the key step to form the trans-THF F-ring. Overall, the FG fragment, which contains six stereogenic centres, was achieved in 18 total synthetic steps (13 longest linear sequence).

trans-2,5-Disubstituted tetrahydrofurans (THFs) are a common structural motif in a multitude of biologically active natural products. This thesis explores new synthetic routes for their synthesis and subsequent application towards the C_31-40 fragment of pectenotoxin-4. Chapter 1: Introduction This chapter reviews methods for the synthesis of trans-2,5-disubstituted tetrahydrofurans with a special emphasis on those that have been applied towards the synthesis of natural products. Chapter 2: Results and Discussion The Acyloin Coupling Reaction towards trans-THFs A brief overview of the acyloin coupling reaction is followed by description of the aim for this part of the project, using this process as a key step towards trans-THFs. Work directed towards the stereoselective protonation of the bis-enolate intermediate formed during the acyloin coupling is discussed. The exploitation of A^1,3 strain was the most effective strategy found to control the diastereoselectivity in the protonation of the bis-enolate intermediate. Desymmetrisation Using Sharpless Asymmetric Epoxidation towards trans-THFs Strategy developed towards the synthesis of a 2,5-disubstituted 3-hydroxy trans-THF is studied. The optimisation of the synthesis of meso-hepta-1,6-diene-3,5-diol was examined and subsequent desymmetrisation using the Sharpless asymmetric epoxidation was explored. Approaches towards the FG Fragment of Pectenotoxin-4 The previous synthesis of the FG fragment was reviewed. Details of the retrosynthesis to be employed for the preparation of the southern hemisphere of pectenotoxin-4 are discussed. The desymmetrisation strategy previously explored was applied towards forming the F ring of pectenotoxin-4. The C_31-40 carbon skeleton was successfully formed in 12 steps using a convergent synthesis. The elucidation of an X-ray crystal structure requires further exploration to confirm the relative and absolute configuration of the THF formed. Chapter 3: Experimental Full experimental procedures and characterisation of compounds are reported.