Development of a rapid and sensitive HPLC method for the identification and quantification of cavoxin and cavoxone in <i>Phoma cava</i> culture filtrates

<p>Cavoxin is a tetrasubstituted phytotoxic chalcone and cavoxone is the corresponding chroman-4-one, both produced <i>in vitro</i> by <i>Phoma cava</i>, a fungus isolated from chestnut. Cavoxin showed biofungicide potential against fungal species responsible for food moulding. Therefore, cavoxin has potential to be incorporated into biopolymer to generate ‘intelligent food packaging’. To reach this objective, large-scale production of cavoxin by <i>P. cava</i> fermentation needs to be optimized. A rapid and efficient method for cavoxin analysis, as well as of cavoxone, in the fungal culture filtrates and the corresponding organic extracts is the first experimental step. Thus, a HPLC method was developed and applied to quantify cavoxin and cavoxone production in two different fungal culture conditions. The analysis proved that cavoxin production in stirred culture filtrates is significantly higher than in static ones.</p

Gulypyrones A and B and Phomentrioloxins B and C Produced by <i>Diaporthe gulyae</i>, a Potential Mycoherbicide for Saffron Thistle (<i>Carthamus lanatus</i>)

A virulent strain of <i>Diaporthe gulyae</i>, isolated from stem cankers of sunflower and known to be pathogenic to saffron thistle, has been shown to produce both known and previously undescribed metabolites when grown in either static liquid culture or a bioreactor. Together with phomentrioloxin, a phytotoxic geranylcyclohexenetriol recently isolated from a strain of <i>Phomopsis</i> sp., two new phytotoxic trisubstituted α-pyrones, named gulypyrones A and B (<b>1</b> and <b>2</b>), and two new 1,<i>O</i>- and 2,<i>O</i>-dehydro derivatives of phomentrioloxin, named phomentrioloxins B and C (<b>3</b> and <b>4</b>), were isolated from the liquid culture filtrates of <i>D. gulyae</i>. These four metabolites were characterized as 6-[(2<i>S</i>)­2-hydroxy-1-methylpropyl]-4-methoxy-5-methylpyran-2-one (<b>1</b>), 6-[(1<i>E</i>)-3-hydroxy-1-methylpropenyl]-4-methoxy-3-methylpyran-2-one (<b>2</b>), 4,6-dihydroxy-5-methoxy-2-(7-methyl-3-methylene­oct-6-en-1-ynyl)­cyclohex-2-enone (<b>3</b>), and 2,5-dihydroxy-6-methoxy-3-(7-methyl-3-methylene­oct-6-en-1-ynyl)­cyclohex-3-enone (<b>4</b>) using spectroscopic and chemical methods. The absolute configuration of the hydroxylated secondary carbon of the 2-hydroxy-1-methylpropyl side chain at C-6 of gulypyrone A was determined as <i>S</i> by applying a modified Mosher’s method. Other well-known metabolites were also isolated including 3-nitropropionic, succinic, and <i>p</i>-hydroxy- and <i>p</i>-methylbenzoic acids, <i>p</i>-hydroxybenzaldehyde, and nectriapyrone. When assayed using a 5 mM concentration on punctured leaf disks of weedy and crop plants, apart from 3-nitropropionic acid (the main metabolite responsible for the strong phytotoxicity of the culture filtrate), phomentrioloxin B caused small, but clear, necrotic spots on a number of plant species, whereas gulypyrone A caused leaf necrosis on <i>Helianthus annuus</i> plantlets. All other compounds were weakly active or inactive

Lathyroxins A and B, Phytotoxic Monosubstituted Phenols Isolated from <i>Ascochyta lentis</i> var. <i>lathyri</i>, a Fungal Pathogen of Grass Pea (<i>Lathyrus sativus</i>)

<i>Ascochyta lentis</i> var. <i>lathyri</i> has recently been reported to be the causal agent of Ascochyta blight of grass pea (<i>Lathyrus sativus</i>), a disease characterized by the appearance of necrotic lesions of leaves and stems. Considering the novelty of the pathogen and the possible involvement of secondary metabolites in symptom appearance, a study was carried out to ascertain the capability of this fungus to produce bioactive metabolites. Some phytotoxic phenols were isolated from the culture filtrates of the fungus. In particular, two new phytotoxic metabolites, named lathyroxins A and B, were characterized by spectroscopic methods as 4-(2-hydroxy-3,3-dimethoxypropyl)­phenol and 3-(4-hydroxyphenyl)­propane-1,2-diol, respectively, and the <i>R</i> absolute configuration of C-2 of their 2-dimethoxy- and 2,3-diol-propyl side chain was assigned. Moreover, other well-known fungal metabolites, namely, <i>p</i>-hydroxybenzaldehyde, <i>p</i>-methoxyphenol, and tyrosol, were also identified. Lathyroxins A and B showed interesting phytotoxic properties, being able to cause necrosis on leaves and to inhibit seed germination and rootlet elongation. Moreover, both of the new metabolites had no effect against bacteria, arthropods, and nematodes

Phomentrioloxin, a Fungal Phytotoxin with Potential Herbicidal Activity, and its Derivatives: A Structure–Activity Relationship Study

Phomentrioloxin is a phytotoxic geranylcyclohexenetriol produced in liquid culture by <i>Phomopsis</i> sp. (teleomorph: <i>Diaporthe gulyae</i>), a potential mycoherbicide proposed for the control of the annual weed <i>Carthamus lanatus.</i> In this study, seven derivatives obtained by chemical modifications of the toxin were assayed for phytotoxic, antimicrobial, and zootoxic activities, and the structure–activity relationships were examined. Each compound was tested on nonhost weedy and agrarian plants, fungi, Gram+ and Gram– bacteria, and on brine shrimp larvae. The results provide insights into an investigation of the structural requirements for activity. The hydroxy groups at C-2 and C-4 appeared to be important features for the phytotoxicity, as well as an unchanged cyclohexentriol ring. A role seemed also to be played by the unsaturations of the geranyl side chain. These findings could be useful for understanding the mechanisms of action of new natural products, for identifying the active sites, and possibly in devising new herbicides of natural origin

Higginsianins A and B, Two Diterpenoid α‑Pyrones Produced by <i>Colletotrichum higginsianum</i>, with <i>in Vitro</i> Cytostatic Activity

Two new diterpenoid α-pyrones, named higginsianins A (<b>1</b>) and B (<b>2</b>), were isolated from the mycelium of the fungus <i>Colletotrichum higginsianum</i> grown in liquid culture. They were characterized as 3-[5a,9b-dimethyl-7-methylene-2-(2-methylpropenyl)­dodecahydro­naphtho­[2,1-<i>b</i>]­furan-6-ylmethyl]-4-hydroxy-5,6-dimethylpyran-2-one and 4-hydroxy-3-[6-hydroxy-5,8a-dimethyl-2-methylene-5-(4-methylpent-3-enyl)­decahydro­naphthalen-1-ylmethyl]-5,6-dimethylpyran-2-one, respectively, by using NMR, HRESIMS, and chemical methods. The structure and relative configuration of higginsianin A (<b>1</b>) were confirmed by X-ray diffractometric analysis, while its absolute configuration was assigned by electronic circular dichroism (ECD) experiments and calculations using a solid-state ECD/TDDFT method. The relative and absolute configuration of higginsianin B (<b>2</b>), which did not afford crystals suitable for X-ray analysis, were determined by NMR analysis and by ECD in comparison with higginsianin A. <b>1</b> and <b>2</b> were the C-8 epimers of subglutinol A and diterpenoid BR-050, respectively. The evaluation of <b>1</b> and <b>2</b> for antiproliferative activity against a panel of six cancer cell lines revealed that the IC₅₀ values, obtained with cells reported to be sensitive to pro-apoptotic stimuli, are by more than 1 order of magnitude lower than their apoptosis-resistant counterparts (1 vs >80 μM). Finally, three hemisynthetic derivatives of <b>1</b> were prepared and evaluated for antiproliferative activity. Two of these possessed IC₅₀ values and differential sensitivity profiles similar to those of <b>1</b>

Higginsianins A and B, Two Diterpenoid α‑Pyrones Produced by <i>Colletotrichum higginsianum</i>, with <i>in Vitro</i> Cytostatic Activity

Two new diterpenoid α-pyrones, named higginsianins A (<b>1</b>) and B (<b>2</b>), were isolated from the mycelium of the fungus <i>Colletotrichum higginsianum</i> grown in liquid culture. They were characterized as 3-[5a,9b-dimethyl-7-methylene-2-(2-methylpropenyl)­dodecahydro­naphtho­[2,1-<i>b</i>]­furan-6-ylmethyl]-4-hydroxy-5,6-dimethylpyran-2-one and 4-hydroxy-3-[6-hydroxy-5,8a-dimethyl-2-methylene-5-(4-methylpent-3-enyl)­decahydro­naphthalen-1-ylmethyl]-5,6-dimethylpyran-2-one, respectively, by using NMR, HRESIMS, and chemical methods. The structure and relative configuration of higginsianin A (<b>1</b>) were confirmed by X-ray diffractometric analysis, while its absolute configuration was assigned by electronic circular dichroism (ECD) experiments and calculations using a solid-state ECD/TDDFT method. The relative and absolute configuration of higginsianin B (<b>2</b>), which did not afford crystals suitable for X-ray analysis, were determined by NMR analysis and by ECD in comparison with higginsianin A. <b>1</b> and <b>2</b> were the C-8 epimers of subglutinol A and diterpenoid BR-050, respectively. The evaluation of <b>1</b> and <b>2</b> for antiproliferative activity against a panel of six cancer cell lines revealed that the IC₅₀ values, obtained with cells reported to be sensitive to pro-apoptotic stimuli, are by more than 1 order of magnitude lower than their apoptosis-resistant counterparts (1 vs >80 μM). Finally, three hemisynthetic derivatives of <b>1</b> were prepared and evaluated for antiproliferative activity. Two of these possessed IC₅₀ values and differential sensitivity profiles similar to those of <b>1</b>