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A bioactive disubstituted nonenolide, named truncatenolide, was produced by Colletotrichum truncatum, which was collected from infected tissues of soybean showing anthracnose symptoms in Argentina. This is a devastating disease that drastically reduces the yield of soybean production in the world. The fungus also produced a new trisubstituted oct-2-en-4-one, named truncatenone, and the well-known tyrosol and N-acetyltyramine. Truncatenolide and truncatenone were characterized by spectroscopic (essentially one-dimensional (1D) and two-dimensional (2D) 1H and 13C NMR and HR ESIMS) and chemical methods as (5E,7R,10R)-7-hydroxy-10-methyl-3,4,7,8,9,10-hexahydro-2H-oxecin-2-one and (Z)-6-hydroxy-3,5-dimethyloct-2-en-4-one, respectively. The geometry of the double bond of truncatenolide was assigned by the value of olefinic proton coupling constant and that of truncatenone by the correlation observed in the corresponding NOESY spectrum. The relative configuration of each stereogenic center was assigned with the help of 13C chemical shift and 1H-1H scalar coupling DFT calculations, while the absolute configuration assignment of truncatenolide was performed by electronic circular dichroism (ECD). When tested on soybean seeds, truncatenolide showed the strongest phytotoxic activity. Tyrosol and N-acetyltyramine also showed phytotoxicity to a lesser extent, while truncatenone weakly stimulated the growth of the seed root in comparison to the control. When assayed against Macrophomina phaseolina and Cercospora nicotianae, other severe pathogens of soybean, truncatenolide showed significant activity against M. phaseolina and total inhibition of C. nicotianae. Thus, some other fungal nonenolides and their derivatives were assayed for their antifungal activity against both fungi in comparison with truncatenolide. Pinolidoxin showed to a less extent antifungal activity against both fungi, while modiolide A selectively and totally inhibited only the growth of C. nicotianae. The SAR results and the potential of truncatenolide, modiolide A, and pinolidoxin as biofungicides were also discussed.

Biotic stresses (fungi, bacteria, insects, weeds, etc.) are some of the most important causes of the decrease in the quality and quantity of crops that could become an emergency due to a noteworthy increase in the world population. Thus, to overcome these problems, massive use of chemical pesticides has been carried out with heavy consequences for environmental pollution and food safety. An eco-friendly alternative can be using natural compound-based biopesticides with high efficacy and selectivity. Some bacterial lipodepsipeptides (tolaasins I, II, A, D, and E and WLIP together with hexacetyl- and tetrahydro-tolaasin I and WLIP methyl ester) and cyclic dipeptides (cyclo(l-Pro-l-Tyr), cyclo(d-Pro-l-Tyr), cyclo(l-Pro-l-Val), and cyclo(l-Pro-l-Leu)) were assayed against several pathogenic bacteria and fungi of important agrarian plants. Lipodepsipeptides showed strong growth inhibition of all microorganisms tested in the range of 0.1-0.8 μg/mL, while cyclodipeptides, despite preserving this ability, showed a noteworthily reduced antimicrobial activity being active only in the range of 15-900 μg/mL. Among the lipodepsipeptides and cyclic dipeptides assayed, tolaasin d and cyclo(l-Pro-l-Tyr) (also named maculosin-1) appeared to be the most toxic compounds. Some structure-activity relationships of lipodepsipeptides were also discussed along with their practical application as biopesticides in agriculture.

Phytotoxic metabolites produced in liquid culture by six species of Lasiodiplodia isolated in Brazil and causing Botryosphaeria dieback of grapevine were chemically identified. As ascertained by LC/MS, L. brasiliense, L. crassispora, L. jatrophicola, and L. pseudotheobromae produced jasmonic acid, and L. brasiliense synthesized, besides jasmonic acid, also (3R,4S)-4-hydroxymellein. L. euphorbicola and L. hormozganensis produced some low molecular weight lipophilic toxins. Specifically, L. euphorbicola produced (-)-mellein, (3R,4R)-(-)- and (3R,4S)-(-)-4-hydroxymellein, and tyrosol, and L. hormozganensis synthesized tyrosol and p-hydroxybenzoic acid. This is the first report on the production of the above cited metabolites from L. euphorbicola and L. hormozganensis. The phytotoxic activity of the metabolites produced is also discussed and related to the symptoms these pathogens cause in the grapevine host plants.

Grapevines are produced worldwide with important impact on local economies. Several biotic stresses induce serious diseases of grapevine, which severly affect the quantity and the quality of production. One of the most important problems of vineyards worldwide is the high incidence of grapevine trunk diseases (GTD) induced by fungi belonging to several genera. Environmental-friendly methods for GTD control are being studied. This manuscript offers a perspective and an advanced overview on the fungal phytotoxins involved in GTD and their eventual role in the development of disease symptoms.

Polyphenols were characterized from Dothiorella vidmadera (DAR78993), which was isolated from a grapevine in Australia. In total, six polyphenols were isolated including a new polyphenol characterized by a spectroscopic method (essentially NMR and HR ESIMS) as 5-hydroxymethyl-2-isopropoxyphenol. Tyrosol, benzene-1,2,4-triol, resorcinol, 3-(hydroxymethyl)phenol, and protocatechuic alcohol, the latter being the main metabolite, were also isolated. Although these are already known as naturally occurring compounds in microorganisms and plants, this is the first time they have been isolated from fungal organisms involved in grapevine trunk disease. When assayed on tomato seedlings, all the compounds show similar phytotoxic effects. However, when assayed on grapevine leaves (Vitis vinifera cv Shiraz), resorcinol was the most toxic compound, followed by protocatechuic alcohol and 5-hydroxymethyl-2-isopropoxyphenol.

Three new polycyclic ethanones, named alternethanoxins C-E, were isolated together with the well-known and closely related alternethanoxins A and B, from the solid culture of Alternaria sonchi, a fungal pathogen proposed for perennial sowthistle (Sonchus arvensis L.) biocontrol. Alternethanoxins C-E were characterized by spectroscopic methods (essentially NMR and HRESI MS) as 2'-dihydroxymethyl-2,5,6,6'-tetrahydroxy-3'-methoxy-biphenyl-3-carboxylic acid methyl ester, 1,4,6,9,10-pentahydroxy-7-methoxy-6H-benzo[c]chromene-2-carboxylic acid methyl ester, and 7,9-dihydroxy-2-methoxy-9H-4,8-dioxa-cyclopenta[def]phenanthrene-5-carboxylic acid methyl ester. When assayed on leaf segments of weeds (Sonchus arvensis and Elytrigia repens), alternethanoxins A and C showed phytotoxic activity inducing notable necrotic lesions. Alternethanoxins C and D possess notable antimicrobial activity when tested against Bacillus subtilis (MIC 10 μg/disc) and Candida tropicalis (MIC 25 μg/disc). Alternethanoxins A and B had low activity against these microbes, while alternethanoxin E was inactive.

Orobanche and Phelipanche species (the broomrapes) are root parasitic plants, some of which cause heavy yield losses on important crops. The development of herbicides based on natural metabolites from microbial and plant origin, targeting early stages on parasitic plant development, might contribute to the reduction of broomrape seed bank in agricultural soils. Therefore, the effect of metabolites belonging to different classes of natural compounds on broomrape seed germination and radicle development was assayed in vitro. Among the metabolites tested, epi-sphaeropsidone, cyclopaldic acid, and those belonging to the sesquiterpene class induced broomrape germination in a species-specific manner. epi-Epoformin, sphaeropsidin A, and cytochalasans inhibited germination of GR24-treated broomrape seeds. The growth of broomrape radicle was strongly inhibited by sphaeropsidin A and compounds belonging to cyclohexene epoxide and cytochalasan classes. Broomrape radicles treated with epi-sphaeropsidone developed a layer of papillae while radicles treated with cytochalasans or with sphaeropsidin A turned necrotic. These findings allow new lead natural herbicides for the management of parasitic weeds to be identified., The research was carried out in part in the frame of Programme STAR, financially supported by UniNA and Compagnia di San Paolo, and in part in the frame of project FP7-ARIMNetMEDILEG. This work was carried out within the COST ACTION FA1206 Strigolactones: biological roles and applications. Monica Fernandez-Aparicio has received support from the ́ European Union, in the framework of the Marie-Curie FP7 COFUND People Programme, through the award of an AgreenSkills’ fellowship (under grant agreement n° PCOFUNDGA-2010−267196). A. E. is associated with the Istituto di Chimica Biomolecolare del CNR, Pozzuoli, Italy.

A new tetrasubstituted pyran-2-one and a new dihydrobenzofuran, named colletochlorins E and F (1 and 2, respectively), were isolated from the culture filtrates of the fungus Colletotrichum higginsianum together with the already known colletochlorin A, 4-chloroorcinol, and colletopyrone. Colletochlorin E, the main metabolite, and colletochlorin F were characterized by spectroscopic (NMR, HRESIMS) and chemical methods as 3-[7-chloro-4-hydroxy-2-(1-hydroxy-1-methylethyl)-6-methyl-2,3-dihydrobenzofuran-5-ylmethyl]-4-hydroxy-5,6-dimethylpyran-2-one and 7-chloro-2-(1-hydroxy-1-methylethyl)-6-methyl-2,3-dihydrobenzofuran-4-ol, respectively. The absolute configuration 2′S of 1 was deduced by X-ray diffractometric analysis, whereas 2S of 2 was deduced by comparison of its NMR and CD data with those of 1. When assayed by leaf puncture on Sonchus arvensis and tomato leaves, 2 caused quite large necrosis (>1 cm), whereas 4-chloroorcinol proved to be the most active compound. These results were confirmed by those obtained in assays on Lemna minor and Phelipanche ramosa seed germination. Furthermore 1, colletochlorin A and colletopyrone were less or modestly active in the latter assay, respectively. Interestingly, the phytotoxicity was not associated with an antibiotic activity, whereas only 4-chloroorcinol and colletochlorin F exhibited zootoxic activity.

Orobanche crenata is a parasitic weed that causes severe yield losses in important grain and forage legume crops. Cereals have been reported to inhibit O. crenata parasitism when grown intercropped with susceptible legumes, but the responsible metabolites have not been identified. A number of metabolites have been reported in cereals that have allelopathic properties against weeds, pests, and pathogens. We tested the effect of several allelochemicals identified in cereals on O. crenata seed germination and radicle development. We found that 2-benzoxazolinone, its derivative 6-chloroacetyl-2-benzoxazolinone, and scopoletin significantly inhibited O. crenata seed germination. Benzoxazolinones, l-tryptophan, and coumalic acid caused the stronger inhibition of radicle growth. Also, other metabolites reduced radicle length, this inhibition being dose-dependent. Only scopoletin caused cell necrotic-like darkening in the young radicles. Prospects for their application to parasitic weed management are discussed. © 2013 American Chemical Society., This research is supported by projects FP7-ARIMNet-MEDILEG and AGL2011-22524 (cofinanced by FEDER funds).

Agropyrenol is a phytotoxic substituted salicylic aldehyde produced in liquid culture by Ascochyta agropyrina var. nana , a potential mycoherbicide proposed for the control of the perennial weed Elytrigia repens. In this study, six 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 non-host weedy and agrarian plants, fungi, Gram-positive and Gram-negative bacteria, and brine shrimp larvae. The results provide insights into the structure-activity relationships of agropyrenol. Both the double bond and the diol system of the 3,4-dihydroxypentenyl side chain as well as the aldehyde group at C-1 of the phenolic ring of agropyrenol proved to be important for the phytotoxicity. The lesser polar 3',4'-O,O'-isopropylidene of agropyrenol also showed significant zootoxic and slight antimicrobial activities. This finding could be useful in devising new natural herbicides for practical application in agriculture.

The Gram-negative bacterium Flavobacterium columnare is the cause of columnaris disease, which can occur in channel catfish ( Ictalurus punctatus ). In a previous study, the betaine-type alkaloid ungeremine, 1, obtained from Pancratium maritimum L. was found to have strong antibacterial activity against F. columnare. In this study, analogues of 1 were evaluated using a rapid bioassay for activity against F. columnare to determine if the analogues might provide greater antibacterial activity and to determine structure-activity relationships of the test compounds. Several ungeremine analogues were prepared by hydrochlorination of the alkaloid and by selenium dioxide oxidation of both lycorine, 7, and pseudolycorine, 8, which yielded the isomer of ungeremine, 3, and zefbetaine, 4, respectively. The treatment of lycorine with phosphorus oxychloride allowed the synthesis of an anhydrolycorine lactam, 5, showing, with respect to 1, the deoxygenation and oxygenation of C-2 and C-7 of the C and B rings, respectively. The results of the structure-activity relationship studies showed that the aromatization of the C ring and the oxidation to an azomethine group of C-7 of the B ring are structural features important for antibacterial activity. In addition, the position of the oxygenation of the C ring as well as the presence of the 1,3-dioxole ring joined to the A ring of the pyrrolo[de]phenanthridine skeleton also plays a significant role in imparting antibacterial activity. On the basis of 24-h 50% inhibition concentration (IC(50)) results, ungeremine hydrochloride, 2, was similar in toxicity to 1, whereas 5 had the lowest activity. Analogue 2 is soluble in water, which may provide the benefit for use as an effective feed additive or therapeutant compared to ungeremine.

Three new polycyclic ethanones, named alternethanoxins C-E, were isolated together with the well-known and closely related alternethanoxins A and B, from the solid culture of Alternaria sonchi, a fungal pathogen proposed for perennial sowthistle (Sonchus arvensis L.) biocontrol. Alternethanoxins C-E were characterized by spectroscopic methods (essentially NMR and HRESI MS) as 2'-dihydroxymethyl-2,5,6,6'-tetrahydroxy-3'-methoxy-biphenyl-3-carboxylic acid methyl ester, 1,4,6,9,10-pentahydroxy-7-methoxy-6H-benzo[c]chromene-2-carboxylic acid methyl ester, and 7,9-dihydroxy-2-methoxy-9H-4,8-dioxa-cyclopenta[def]phenanthrene-5-carboxylic acid methyl ester. When assayed on leaf segments of weeds (Sonchus arvensis and Elytrigia repens), alternethanoxins A and C showed phytotoxic activity inducing notable necrotic lesions. Alternethanoxins C and D possess notable antimicrobial activity when tested against Bacillus subtilis (MIC 10 μg/disc) and Candida tropicalis (MIC 25 μg/disc). Alternethanoxins A and B had low activity against these microbes, while alternethanoxin E was inactive.