Graziano Guella | University of Trento (original) (raw)

Papers by Graziano Guella

In eukaryotic cells the ubiquitous thioredoxin reductase-thioredoxin system (TrxR-Trx) catalyses ... more In eukaryotic cells the ubiquitous thioredoxin reductase-thioredoxin system (TrxR-Trx) catalyses substrate disulfide reduction using NADPH as a source of reducing equivalents. Thioredoxin forms a superfamily with several other proteins sharing little sequence similarity but possessing a common active site. Among these, protein disulfide isomerase (PDI) is colocalized, in cells,with TrxR and there are now some in vitro evidences that PDI can be a substrate of TrxR1. To further demonstrate this interaction we have now produced a fluorogenic substrate suitable to test TrxR-dependent PDI activity. The substrate was formed by two identical cys-containing tri-peptides linked at the N-terminus to a molecule of fluorescein-5-isothiocyanate (FITC) and held together by a disulfide bridge between the cysteines; it was called pep-FITC. The reduction of pep-FITC was measured at 25\ub0C in a Fluoromax spectrofluorimeter and was demonstrated by an increase of the FITC fluorescence at 520nm with excitation at 494nm. We could show that the TrxR-PDI system successfully reduced pep-FITC, while the isolated components did not. Further proofs of the interaction between PDI and TrxR were obtained by fluorescence resonant energy transfer (FRET). In this case we labelled the enzymes with Alexa Fluor 546 and Alexa Fluor 488 respectively, two dyes forming a donor/acceptor pair with a Forster distance of 58 \uc5.A FRET was observed under suitable conditions confirming tight interaction

Fluorescent Assay to Demonstrate the Interaction of Thioredoxin Reductase and Protein Disulfide I... more Fluorescent Assay to Demonstrate the Interaction of Thioredoxin Reductase and Protein Disulfide Isomerase Tomazzolli R.1, Guella G.2, Bellisola G.3, Colombatti M.3 and Menestrina G.1 1: ITC-CNR IBF Unit at Trento, Via Sommarive 18, 38050 Povo (TN), Italy 2: Lab Bioorg Chem, Dep Physics, Uni Trento, Via Sommarive 14, 38050 Povo, Italy 3: Dep Pathology, Sect of Immunol, Uni Verona, L.go Scuro 10, 37134 Verona, Italy In eukaryotic cells, the ubiquitous thioredoxin reductase-thioredoxin system (TrxR-Trx) and the glutathione reductase-glutathione system (GSHR-GSSG) catalyse substrate disulfide reduction using NADPH as a source of reducing equivalents. TrxR reduces the redox protein Trx as well as other endogenous and exogenous compounds, while the glutathione system plays a key role in protecting cellular macromolecules from damage caused by reactive oxygen species. Due to a second redox-active site, mammalian TrxR has a broader substrate specificity than glutathione reductase and Escherichia coli TrxR [1]. Thioredoxin forms a superfamily with several other proteins sharing little sequence similarity but possessing a common active site [2]. Among these, protein disulfide isomerase (PDI) is colocalized, in cells, with TrxR. In vitro there are now some evidences that PDI can be a substrate of TrxR [3, 4]. To further demonstrate this interaction we have produced a fluorogenic substrate suitable to test TrxR-dependent PDI activity. The substrate is constituted by two identical cys-containing tri-peptides linked at the N-terminus to a molecule of fluorescein-5-isothiocyanate (FITC) and held together by a disulfide bridge between the cysteines. The preparation follows a few steps: the tri-peptide is labelled with FITC; it is separated from FITC excess by two reverse phase liquid chromatography elutions and analysed by electrospray ionization mass spectrometry (ESI-MS); oxidation occurs spontaneously or is induced by DMSO. The final substrate, named pep-FITC, is characterized by NMR and ESI-MS. The reduction of pep-FITC was measured at 25\ub0C in a Fluoromax spectrofluorimeter and was indicated by an increase of the FITC fluorescence at 520nm with excitation at 494nm. All the fluorescence measurements were taken in NaP 0.1M, EDTA 2mM pH 7.5. We demonstrated that the TrxR (both mammalian and bacterial)-PDI system successfully reduced pep-FITC while the single components didn\u2019t. GSHR didn\u2019t reduce pep-FITC, in spite of its aminoacidic sequence similarity to GSSG but was active on a fluorogenic GSSG, labelled at N-termini with FITC, thus demonstrating the narrow substrate specificity of GSHR. Further proofs of the interaction between PDI and TrxR we obtained by fluorescence resonant energy transfer (FRET). In this case we labelled the enzymes with Alexa Fluor 546 and Alexa Fluor 488 respectively, two dyes forming a donor/acceptor pair with a Forster distance of 58 \uc5 [5]. A FRET was observed under suitable conditions confirming tight interaction. (1) Mustacich D, Powis G. 2000. Biochem. J., 346: 1-8. (2). Hirota K, Nakamura H, Masutani H, Yodoi J. 2002. Ann. NY Acad. Sci., 957:189-99. (3). Lundstrom J, Holmgren A. 1990. J. Biol. Chem., 265: 9114-9120. (4). Bellisola G, Fracasso G, Ippoliti R, Menestrina G, Rosen A, Solda S, Udali S, Tomazzolli R, Tridente G, Colombatti M. 2004. Biochem. Pharmacol., 67: 1721-1731. (5). Epe B, Steinhauser KG, Woolley P. 1983. Proc. Natl. Acad. Sci. USA 80 (May), 2579-2583

Journal of Eukaryotic Microbiology, 2022

Ciliates are a rich source of molecules synthesized to socialize, compete ecologically, and inter... more Ciliates are a rich source of molecules synthesized to socialize, compete ecologically, and interact with prey and predators. Their isolation from laboratory cultures is often straightforward, permitting the study of their mechanisms of action and their assessment for applied research. This review focuses on three classes of these bioactive molecules: (i) water‐borne, cysteine‐rich proteins that are used as signaling pheromones in self/nonself recognition phenomena; (ii) cell membrane‐associated lipophilic terpenoids that are used in interspecies competitions for habitat colonization; (iii) cortical granule‐associated molecules of various chemical nature that primarily serve offence/defense functions.

Journal of Nanoscience and Nanotechnology, 2016

Thiol-functionalized oligosilsesquioxanes have been synthesized by sol-gel chemistry via the in-s... more Thiol-functionalized oligosilsesquioxanes have been synthesized by sol-gel chemistry via the in-situ water production (ISWP) approach, exploiting the esterification reaction of chloro-acetic acid and 1-propanol. The extent of hydrolysis-condensation of 3-Mercaptopropyltrimethoxysilane (McPTMS) has been studied by FT-IR and NMR spectroscopy, gel permeation chromatography (GPC) and MALDI-TOF techniques. The esterification reaction plays a key role in ruling out the oligomer structural development. In this work, we have investigated the influence of the theoretical amount of water available for the organosilane hydrolysis, defined by the ratio of chloro-acetic acid to McPTMS in the reaction mixture, and the role of different catalysts like trifluoroacetic acid (TFA) and dibutyldilauryltin (DBTL). The behavior of the catalyst is complex since, according to its nature, it may improve the kinetics of the sol-gel reactions and the esterification reaction as well. Comparing the reactions carried out with under-stoichiometric water content, the degree of condensation of the silsesquioxanes is higher if the reaction is catalyzed by TFA than by DBTL, because TFA may improve the kinetics of both hydrolysis-condensation and esterification reactions. The use of DBTL in understoichiometric and stoichiometric hydrolytic conditions raises the yield in ladder-like structures. The degree of condensation generally increases increasing the hydrolysis ratio as well as the yield in cage-like structures. However, when an over-stoichiometric amount of water is provided for the sol-gel reaction, condensation degree and ratio among cages and ladder-like structures appear unaffected by the employed catalyst.

Biology

Heterotrich ciliates typically retain toxic substances in specialized ejectable organelles, calle... more Heterotrich ciliates typically retain toxic substances in specialized ejectable organelles, called extrusomes, which are used in predator-prey interactions. In this study, we analysed the chemical defence strategy of the freshwater heterotrich ciliate Stentor polymorphus against the predatory ciliate Coleps hirtus, and the microturbellarian flatworm Stenostomum sphagnetorum. The results showed that S. polymorphus is able to defend itself against these two predators by deploying a mix of bioactive sterols contained in its extrusomes. Sterols were isolated in vivo and characterized by liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR), as ergosterol, 7-dehydroporiferasterol, and their two peroxidized analogues. The assessment of the toxicity of ergosterol and ergosterol peroxide against various organisms, indicated that these sterols are essential for the effectiveness of the chemical defence in S. polymorphus.

Food Chemistry, 2012

Lipid profiles of fish oil extracted from trout heads, spines and viscera using supercritical car... more Lipid profiles of fish oil extracted from trout heads, spines and viscera using supercritical carbon dioxide and Randall extraction with hexane were measured. The amount of unsaturated fatty acids (as a percentage of total fatty acids) was within the range of 72.6-75.3% in all the substrates. A significant presence of the most important omega-3 fatty acids was detected. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content in oil from spines, heads and viscera resulted to be 8.7% and 7.3%, 7.9% and 6.3%, and 6.4% and 6.0%, respectively. A low (≈3%), but worth noting, presence of lipids with omega-1 polyunsaturated fatty chains was observed in all the oils. Finally, significant differences were noticed in the relative amounts of triacylglycerides (TAG), diacylglycerides (DAG) and free fatty acids (FFA). Whereas oil from heads and spines was essentially composed of TAG (≈98%), in viscera oil the molar distribution ratio became TAG:DAG:FFA=87:8:5.

Plasma Processes and Polymers, 2017

We have investigated the treatment of a mixture of fatty acid methyl esters by an RF-plasma jet w... more We have investigated the treatment of a mixture of fatty acid methyl esters by an RF-plasma jet with He-H2O and He-O2 gas feed. We have measured the concentration of the hydroxyl radical in the jet by laser induced fluorescence, looking for correlation with the lipid reactivity. We have detected four product families, whose yields increase with the OH exposure: volatile products, polymerization products, reduced chains and oxidised chains. Theoretical calculations give insights on the radical attack to the lipid chain and show that none of the products can be attributed exclusively to reactions with OH. Therefore, the observed reactant conversion as function of the OH exposure must be interpreted as a qualitative relationship with the total amount of radical species present in the plasma jet.

Acta horticulturae, Apr 1, 2017

Background: The ripening of fleshy fruits is a complex developmental program characterized by ext... more Background: The ripening of fleshy fruits is a complex developmental program characterized by extensive transcriptomic and metabolic remodeling in the pericarp tissues (pulp and skin) making unripe green fruits soft, tasteful and colored. The onset of ripening is regulated by a plethora of endogenous signals tuned to external stimuli. In grapevine and tomato, which are classified as non-climacteric and climacteric species respectively, the accumulation of hydrogen peroxide (H 2 O 2) and extensive modulation of reactive oxygen species (ROS) scavenging enzymes at the onset of ripening has been reported, suggesting that ROS could participate to the regulatory network of fruit development. In order to investigate this hypothesis, a comprehensive biochemical study of the oxidative events occurring at the beginning of ripening in Vitis vinifera cv. Pinot Noir has been undertaken. Results: ROS-specific staining allowed to visualize not only H 2 O 2 but also singlet oxygen (1 O 2) in berry skin cells just before color change in distinct subcellular locations, i.e. cytosol and plastids. H 2 O 2 peak in sample skins at véraison was confirmed by in vitro quantification and was supported by the concomitant increase of catalase activity. Membrane peroxidation was also observed by HPLC-MS on galactolipid species at véraison. Mono-and digalactosyl diacylglycerols were found peroxidized on one or both α-linolenic fatty acid chains, with a 13(S) absolute configuration implying the action of a specific enzyme. A lipoxygenase (PnLOXA), expressed at véraison and localizing inside the chloroplasts, was indeed able to catalyze membrane galactolipid peroxidation when overexpressed in tobacco leaves. Conclusions: The present work demonstrates the controlled, harmless accumulation of specific ROS in distinct cellular compartments, i.e. cytosol and chloroplasts, at a definite developmental stage, the onset of grape berry ripening. These features strongly candidate ROS as cellular signals in fruit ripening and encourage further studies to identify downstream elements of this cascade. This paper also reports the transient galactolipid peroxidation carried out by a véraison-specific chloroplastic lipoxygenase. The function of peroxidized membranes, likely distinct from that of free fatty acids due to their structural role and tight interaction with photosynthesis protein complexes, has to be ascertained.

Phytochemistry, May 1, 2012

Yellow passion fruit is one of the most well-known tropical fruits and much of its success comes ... more Yellow passion fruit is one of the most well-known tropical fruits and much of its success comes from its typical aroma. Key compounds in explaining yellow passion fruit scent are volatile thiols. These molecules are reported to be present in several fruits and originate from non-volatile precursors. Such free thiols are particularly appreciated in white wines and considerable efforts have been made to try to maximise their production and understand their biosynthesis. Two main precursors have been identified so far: S-glutathionylated and S-cysteinylated precursors, the latter originating in the breaking down of the glycyl and glutamyl moieties of the former. Improving knowledge about this pathway is currently one of the main challenges in the field of aroma chemistry. Only S-cysteinylated precursors have been reported in the literature for yellow passion fruit, thus much of the biochemical pathway remains unknown. In this paper a combination of organic synthesis, MS and NMR experiments was developed in order to investigate this pathway in yellow passion fruit. The three missing stages leading to the S-cysteinylated precursor were clearly identified. Both intermediate species between S-glutathionyl and S-cysteinyl 3-mercaptohexan-1-ol were found, suggesting that the plant is capable of activating both metabolic routes. The information gained would appear to be crucial for study of this important pathway and for potentially extending this knowledge to other plants, in particular the grapevine.

Plant Pathology, Jun 12, 2012

ABSTRACT Ppdfn1 is a defensin gene previously identified in peach (Prunus persica). The biologica... more ABSTRACT Ppdfn1 is a defensin gene previously identified in peach (Prunus persica). The biological role of Ppdfn1 was investigated by analysing its expression profile in leaves, flowers and fruits, either inoculated with the Monilinia laxa fungal pathogen or mock-inoculated. Ppdfn1 expression was highest in flowers and, in fruits, did not vary upon M. laxa inoculation. To charac-terize the PpDFN1 antifungal activity, the recombinant mature peptide was expressed in Escherichia coli and purified; recombinant PpDFN1 displays antifungal activity against Botrytis cinerea, M. laxa and Penicillium expansum, with IC 50 values of 15AE1, 9AE9 and 1AE1 lg mL)1 , respectively. Treatment of fungal hyphae with FITC-labelled PpDFN1 indicated that the peptide is not internalized by fungal hyphae, but localizes on their external cell surface. At this site, PpDFN1 is capable of membrane destabilization and permeabilization, as demonstrated by SYTOX Green fluorescence uptake by the treated mycelia. Using artificial lipid monolayers, it was shown that PpDFN1 interacts with sphingolipid-containing membranes; however the strongest interaction occurs with monolayers composed of lipids extracted from sensitive fungi, such as P. ex-pansum. These data suggest that the lipid composition of fungal membranes is of key relevance for defensin specificity.

Australian Journal of Grape and Wine Research, Aug 28, 2011

Background and Aims: In the Vitaceae, stilbenoid viniferins constitute a relatively restricted gr... more Background and Aims: In the Vitaceae, stilbenoid viniferins constitute a relatively restricted group of molecules based on a trans-resveratrol structure and represent the main known phytoalexins. The aim of this work was the development of a new method for the chromatographic separation and accurate quantification of viniferins found in grapevine leaves following infection with Plasmopara viticola. Methods and Results: An interspecific F1 population was used, deriving from the cross between Merzling and Teroldego, respectively, partially resistant and susceptible to P. viticola. Analysis was carried on a liquid chromatography-mass spectrometry (LC-MS) system, using a reverse phase column. A method was validated for detailed metabolite profiling, with accurate identification and quantification of trans-resveratrol, trans-piceid, transpterostilbene, a condensation product between (+)-catechin and caffeic acid, and the whole class of stilbenoid viniferins in P. viticola-infected grapevine leaves, using their respective standards. Synthesis was ongoing, and 6 days after infection, it was possible to see the highest concentration of stilbenoids for all genotypes. On the other hand, the intensity of stilbene induction did not show a clear and homogeneous correlation with the position of the leaves in the young shoot. Conclusions: The method described in this paper provides the basis for performing in a single run a targeted analysis of resveratrol, piceid, pterostilbene and the whole class of stilbenoids in P. viticola-infected grapevine genotypes. Significance of the Study: To our knowledge, this is the first paper that has reported on detailed metabolite profiling with accurate identification and quantification of the main viniferins in grape leaves following infection with P. viticola, using the respective standards.

Molecules, Dec 18, 2019

To differentiate extra virgin olive oils (EVOO) according to the origin of purchase, such as mono... more To differentiate extra virgin olive oils (EVOO) according to the origin of purchase, such as monocultivar Italian EVOO with protected denomination of origin (PDO) and commercially-blended EVOO purchased in supermarkets, a number of samples was subjected to the analysis of various lipid species by liquid chromatography/mass spectrometry (LC-ESI-MS/MS, LC-ESI-IT-MS) and proton nuclear magnetic resonance analysis (1 H-NMR). Many putative chemical markers were extracted as differentiators by uni-and multivariate statistical analysis. Commercially-blended EVOO contained higher concentrations of the majority of minor lipids, including free fatty acids, their alkyl (methyl and ethyl) esters, monoglycerides, and diglycerides, which may be indicative of a higher degree of triglyceride lipolysis in these than in monocultivar PDO EVOO. Triterpenoids and particular TAG species were also found in higher proportions in the samples from the commercially-blended EVOO class, suggesting a possible influence of factors such as the cultivar and geographical origin. The largest differences between the classes were determined for the concentrations of uvaol and oleanolic acid. The results of the analysis by isotopic ratio mass spectrometry (IRMS) were reasonably consistent with the information about the geographical origin declared on the labels of the investigated EVOOs, showing considerable variability, which possibly also contributed to the differences in lipid composition observed between the two investigated classes of EVOO.

ACS Omega, 2019

The increasing popularity of "Mirto" liqueur, produced from Myrtus communis berries, has led to t... more The increasing popularity of "Mirto" liqueur, produced from Myrtus communis berries, has led to the planting of domesticated cultivars, expanding myrtle berry production. To promote the use of cultivated berries, the content in the nutraceutical compounds ellagitannins has been investigated both in spontaneous and cultivated fruits. Oenothein B and eugeniflorin D 2 , characterized by 1 H and 13 C NMR, were isolated and quantified using ultrahigh-performance liquid chromatography−diode array detector−tandem mass spectrometry (UPLC−DAD−MS/MS). The antifungal and anti-inflammatory activities of oenothein B were assayed in vitro. Large amounts of oenothein B and eugeniflorin D 2 were detected in seeds (12 ± 2.4 and 5.8 ± 1.2 mg/g). The oenothein B concentration in liqueurs was 194 ± 22 mg/L. This macrocyclic ellagitannin dimer showed anti-Candida (minimal inhibitory concentration <8−64 μg/mL) and anti-inflammatory properties. Cultivated myrtle berries are a source of nutraceutical compounds. The high concentration of oenothein B in liqueur suggests a possible contribution to the organoleptic and biological properties of the beverage.

Journal of Agricultural and Food Chemistry, May 3, 2011

In the Vitaceae, viniferins represent a relatively restricted group of trans-resveratrol oligomer... more In the Vitaceae, viniferins represent a relatively restricted group of trans-resveratrol oligomers with antifungal properties, thus enabling plants to cope with pathogen attack. The aim of this study was to perform isolation and structural characterization of the whole class of viniferins accumulating in the leaves of hybrid Vitis vinifera (Merzling Â Teroldego) genotypes infected with Plasmopara viticola. Infected leaves of resistant plants were collected 6 days after infection, extracted with methanol, and prepurified by flash chromatography using ENVþ and Toyopearl HW 40S resins. Further fractionation using normal-phase preparative chromatography and then reversed-phase preparative chromatography allowed isolation of 14 peaks. The isolated compounds were identified using advanced mass spectrometry techniques and extensive one-and two-dimensional nuclear magnetic resonance measurements, UV, CD, optical properties, and molecular mechanic calculations. The results demonstrated the presence in infected leaves of seven dimers (six stilbenes and one stilbenoid), of which four were new in grapevine (ampelopsin D, quadrangularin A, E-ω-viniferin, and Z-ω-viniferin), four trimers (three stilbenes and one stilbenoid), of which two (Z-miyabenol C and E-cis-miyabenol C) were new in grapevine, three tetramer stilbenoids, all new in grapevine, isohopeaphenol, ampelopsin H, and a vaticanol C-like isomer. The isolation of a dimer deriving from the condensation of (þ)-catechin with trans-caffeic acid also indicated that other preformed phenolics are structurally modified in tissues infected with P. viticola.

Italy-The conversion of natural gas into more useful compounds, represents one of the present-day... more Italy-The conversion of natural gas into more useful compounds, represents one of the present-day most attractive goals. Particularly relevant is the dry reforming process that realizes the simultaneous conversion of methane and carbon dioxide into syngas. Since CH4 and CO2 are both greenhouse gases, this process is of great environmental interest because it couples the advantages of an efficient transformation of natural gas into useful chemicals with the potential positive effects on global warming related to CO2 recycling. In a dielectric barrier discharge of CH4/CO2 at atmospheric pressure, in addition to syngas we have observed the formation of liquid chemicals. This is quite fascinating since the production of liquid fuels by CH4 and CO2 is a very attractive way to store and transport energy. The nature of the liquid has been investigated by using gas-chromatography, infrared spectroscopy and nuclear magnetic resonance spectroscopy. The non volatile component of the liquid products consists of a broad distribution of hydrocarbons, highly branched mainly by methyl groups. In addition we have observed the production of a minor amount (5%) of oxygenated compounds (tertiary alcohols, ketones, esters and carboxylic acids).

Rapid Communications in Mass Spectrometry, 2003

Electrospray ionization-quadrupole ion trap mass spectrometry (ESI-QITMS), either in positive- or... more Electrospray ionization-quadrupole ion trap mass spectrometry (ESI-QITMS), either in positive- or in negative-ion mode, has been used to establish the chemical structures (chain length, degree of unsaturation, positional distribution) of the fatty acids attached to the primary (sn-1) and secondary (sn-2) hydroxyl groups of the glycerol moiety of natural monogalactosyl- (MGDG) and digalactosyldiacylglycerols (DGDG), isolated from the freshwater dinoflagellate Glenodinium sanguineum and from a marine diatom belonging to the genus Chaetoceros. Fragmentation by collision-induced dissociation of a single component in MGDG and DGDG mixtures, separated by high-performance liquid chromatography (HPLC) and detected on-line by tandem positive-ion ESI-MS, leads to a clear-cut determination of the positional distribution of the sn-glycerol-bound fatty acyl chains. Reversed-phase liquid chromatography allowed a partial resolution of the component mixture before ESI-MS/MS analysis. These results were validated by comparison with ESI-MS data obtained for the sn-2 lysoglyceroglycolipids synthesized via regiospecific enzymatic hydrolysis of the corresponding diacylglycerols by Rhizopus arrhizus lipase. Copyright © 2003 John Wiley & Sons, Ltd.

Biochemistry, 2006

The actinoporins are a family of proteins from sea anemones that lyse cells by forming pores in c... more The actinoporins are a family of proteins from sea anemones that lyse cells by forming pores in cell membranes. Sphingomyelin plays an important role in their lytic activity, with membranes lacking this lipid being resistant to these toxins. Pore formation by the actinoporin equinatoxin II (EqTII) proceeds by membrane binding via a surface rich in aromatic residues, followed by translocation of the N-terminal region to the membrane and, finally, across the bilayer to form a functional pore. A key feature of this mechanism is the ability of the N-terminal region to form a stable, bilayer-spanning helix in the membrane, which in turn requires dissociation of the N-terminus from the bulk of the protein and significant extension of the N-terminal helix of native EqTII. In this study the structures of three peptides corresponding to residues 11-29, 11-32, and 1-32, respectively, of EqTII have been investigated by high-resolution nuclear magnetic resonance and Fourier transform infrared spectroscopy. The 32-residue peptide lacks ordered secondary structure in water, but residues 6-28 form a helix in dodecylphosphocholine micelles. Although this helix is long enough to span a bilayer membrane, this peptide and the shorter analogues display limited permeabilizing activity in large unilamellar vesicles and very weak hemolytic activity in human red blood cells. Thus, while the N-terminal region has the structural features required for this unusual mechanism of pore formation, the lack of activity of the isolated N-terminus shows that the bulk of the protein is essential for efficient pore formation by facilitating initial membrane binding, interacting with sphingomyelin, or stabilizing the oligomeric pore.

Helvetica Chimica Acta, 1996

Euplotin C((+)-3), the most abundant of the niche-exploitation terpenoids of the marine ciliate m... more Euplotin C((+)-3), the most abundant of the niche-exploitation terpenoids of the marine ciliate morphospecies Euplotes crassus, was found to undergo degradation in mildly basic H2O/MeOH by initial hydrolysis of the acetate group, followed by, in turn, hydrolytic ring-A and ring-C opening and ring-A reclosure with indiscriminate C(1)/C(15) methanol trapping to give four diastereoisomeric aldehydic hemiacetals 5–8 in similar proportions; 7, as a model for its congeners, proved biologically inactive. From these, the absolute configuration was assigned via Mosher's ester methodology. These processes may be assumed to mimic inactivation of the euplotins in sea water. Degradation of (+)-3 in either stronger base or acidic medium was also examined.

Tetrahedron Letters, 1997