Maria Chiara Zonno

Since 1987, several cytochalasins were isolated from Phoma exigua var. heteromorpha, the causal agent of foliar blight disease of oleander (Nerium oleander L.), and chemically and biologically characterised. During the purification process of a large-scale production of cytochalasins A and B, necessary to continue the study on their anticancer activity, a metabolite having a different carbon skeleton compared to that of cytochalasans, was isolated. It was identified as terpestacin, a well-known toxic fungal stestertepenoid, isolated for the first time from P. exigua var. heteromorpha, by spectroscopic investigation (essentially 1D and 2D ¹H and ¹³C-NMR and ESI MS) and optical methods in comparison with the literature data. Terpestacin and some its derivatives (including a natural one, fusaproliferin) were prepared and tested for their biological activity. Terpestacin and fusaproliferin had some inhibitory effects on seed germination of Phelipanche ramosa, whereas none of the compounds caused phytotoxic effects on weed leaves. Graphical Abstract

Colletotrichum lupini is the causal agent of lupin (Lupinus albus L.) anthracnose, a destructive seed-borne disease affecting stems and pods. Despite that several biological studies have been carried out on this pathogen, the production of secondary metabolites has not yet been investigated. Thus, a strain of C. lupini, obtained from symptomatic stems of L. albus, has been grown in vitro to evaluate its ability to produce bioactive compounds. From its culture filtrates, a 3-substituted indolinone, named lupindolinone, and a 5,6-disubstituted tetrahydro-α-pyrone, named lupinlactone, were isolated together with the known (3R)-mevalonolactone and tyrosol. Lupindolinone and lupinlactone were characterized as 3-ethylindolin-2-one and 5-hydroxy-6-methyltetrahydropyran-2-one by spectroscopic methods (essentially nuclear magnetic resonance [NMR] and high-resolution electrospray ionization mass spectrometry [HR ESI-MS]). The R absolute configuration (AC) at C-5 of lupinlactone was determined by applying the modified Mosher’s method. Thus, considering its relative stereochemistry assigned by NMR spectroscopy, the AC of lupinlactone could be formulated as 5R,6S. Lupindolinone was isolated as racemic mixture as shown by investigation using chiroptical methods. The metabolites were assayed in different biological tests and proved to have some activities at the used concentration.

Inuloxin A is a promising plant phytotoxic sesquiterpene that deserves further studies to evaluate its potential as a bioherbicide. However, its low solubility in water and its bioavailability could hamper its practical applications. For this reason, inuloxin A was complexed with β-cyclodextrins by using three different methods, i.e., kneading, co-precipitation and grinding. The resulted complexes were fully characterized by different techniques such as ¹H NMR, UV-vis, XRD, DSC and SEM, and they were biologically assayed in comparison with the pure compound in several biological systems. The efficacy of the kneading and grinding complexes was similar to that of inuloxin A and these complexes almost completely inhibit Phelipanche ramosa seed germination. The complete solubility in water and the preservation of the biological properties of these two complexes could allow further studies to develop a novel natural herbicide for parasitic plant management based on these formulations.

A strain of the pathogenic fungus Ascochyta lentis isolated from lentil (Lens culinaris) was studied to ascertain its capability to produce bioactive metabolites. From the culture filtrates were found three new anthraquinone derivatives, named lentiquinones A (1), B (2), and C (3), and the known lentisone. From the mycelium, four known analogues were identified, namely pachybasin (in larger amount), ω-hydroxypachybasin, 1,7-dihydroxy-3-methylanthracene-9,10-dione, and phomarin. Lentiquinones A–C were characterized by spectroscopic methods as 3,4,6-trihydroxy-8-methyl-2H-benzo[g]chromene-5,10-dione, 2,3,4,5,10-pentahydroxy-7-methyl-3,4,4a,10-tetrahydroanthracen-9(2H)-one, and its 2-epimer, respectively, and the relative configuration of the two latter compounds was deduced by X-ray diffraction data analysis. The absolute configuration of lentiquinones B and C was determined as (2R,3S,4S,4aS,10R) and (2S,3S,4S,4aS,10R), respectively, by electronic circular dichroism (ECD) in solution and solid state, and TDDFT calculations. When tested by using different bioassays, the novel compounds showed interesting activities. In particular, applied to punctured leaves of host and nonhost plants, the three new compounds and lentisone caused severe necrosis, with lentiquinone A being the most active among the new metabolites. On cress (Lepidium sativum), this latter compound proved to be particularly active in inhibiting root elongation. On Lemna minor all the compounds reduced the content of chlorophyll, with 1,7-dihyroxy-3-methylanthracene-9,10-dione being the most active. The new compounds, together with lentisone, proved to have antibiotic properties.