Phytotoxins produced by Phoma chenopodiicola, a fungal pathogen of Chenopodium album Marco Evidente a , Alessio Cimmino a , Maria Chiara Zonno b , Marco Masi a , Alexander Berestetskyi c , Ernesto Santoro d , Stefano Superchi d , Maurizio Vurro b , Antonio Evidente a,⇑ a Department of Chemical Sciences, University of Naples ‘‘Federico II’’, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Napoli, Italy b Institute of Sciences of Food Production, National Research Council, Via Amendola 122/O, 70125 Bari, Italy c All-Russian Institute of Plant Protection, Russian Academy of Agricultural Sciences, Pushkin, Saint-Petersburg 196608, Russia d Department of Sciences, University of Basilicata, Via dell’Ateneo Lucano 10, 85100 Potenza, Italy article info Article history: Received 24 April 2015 Received in revised form 29 June 2015 Accepted 10 July 2015 Keywords: Chenopodium album Phoma chenopodiicola Phytotoxins Furopyrans ent-Pimaradiene Isocoumarines Herbicides abstract Two phytotoxins were isolated from the liquid culture of Phoma chenopodiicola, a fungal pathogen proposed for the biological control of Chenopodium album, a common worldwide weed of arable crops. The two phy- totoxins appeared to be a new tetrasubstituted furopyran and a new ent-pimaradiene. From the same cul- ture a new tetrasubstituted isocoumarin was also isolated. These compounds were characterized by using spectroscopic (essentially 1D and 2D NMR and HR ESI MS) and chemical methods as 3-(3-methoxy-2,6- dimethyl-7aH-furo[2,3-b]pyran-4-yl)-but-2-en-1-ol (chenopodolan D, 1) (1S,2S,3S,4S,5S,9R,10S,12S,13S)- 1,3,12-triacetoxy-2,hydroxy-6-oxo-ent-pimara-7(8),15-dien-18-oic acid 2,18-lactone (chenopodolin B, 3), and, 4,5,7-trihydroxy-3-methyl-isochroman-1-one (chenisocoumarin, 2) The absolute configuration of chenisocoumarin was assigned by applying an advanced Mosher’s method through the derivatization of its secondary hydroxylated carbon C-4, while that of chenopodolan D by application of quantum mechan- ical calculations of chiroptical (ECD and ORD) properties. When assayed by leaf puncture against non-host weeds, chenopodolan D and chenopodolin B showed phytotoxicity while chenisocoumarin and the 9-O- acetyl derivative of chenopodolan D were inactive. These results confirm that the nature of the side chain at C-4 in chenopodolans, and in particular its hydroxylation, are important features for activity. The activity of chenopodolin B could also be explained by its possible hydrolysis to chenopodolin. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Fungal pathogens responsible for foliar and stem diseases of Chenopodium album L., a worldwide diffused weed of arable crops (Holm et al., 1997) also known as common lambsquarters or fat hen, have been studied both as potential biocontrol agents, and as sources of bioactive metabolites. Ascochyta caulina (P. Karst.) v.d. Aa and v. Kest has been extensively studied for both purposes and, more recently Phoma chenopodiicola. From this latter organism a new phytotoxic unrearranged ent-pimaradiene diterpene, named chenopodolin (Cimmino et al., 2013a), along with three novel tetrasubstituted furopyrans, named chenopodolans A–C (Cimmino et al., 2013b) were recently isolated from liquid culture. The relation between the structural features and the phytotoxic activity against some weeds was determined by biological assay of the natural toxins and some of their hemisynthetic derivatives (Cimmino et al., 2013a,b). A further analysis of the organic extracts of the fungus, aimed both at re-isolating chenopodolans A–C to assign their absolute configuration, and to understand why the phytotoxicity of the extracts was higher than that expected by the content of chenopo- dolin and chenopodolans A–C, was undertaken. This permitted us to determine the presence of further bioactive metabolites and to identify them. In particular this manuscript reports on: (a) the isolation and the chemical characterization of three new metabolites produced by P. chenopodiicola, named chenopodolan D (1), chenisocoumarin (2) and chenopodolin B (3)(Fig. 1); (b) the preliminary studies to evaluate their potential as natural herbicides; (c) the assignment of the absolute configuration of 1 by quantum mechanical calculations of Optical Rotatory Dispersion (ORD) and Electronic Circular Dichroism (ECD), and of 2 by applying an advanced Mosher’s method. http://dx.doi.org/10.1016/j.phytochem.2015.07.008 0031-9422/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: evidente@unina.it (A. Evidente). Phytochemistry 117 (2015) 482–488 Contents lists available at ScienceDirect Phytochemistry journal homepage: www.elsevier.com/locate/phytochem