Secondary metabolites produced by Colletotrichum lupini, the causal agent of anthachnose of lupin (Lupinus spp.)

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.

KEYWORDS:

• Colletotrichum lupini
• indolinone and tetrahydro-α-pyrones derivatives
• lupin anthracnose
• lupindolinone and lupinlactone
• phytotoxins

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Supplementary material

Selection of 1D and 2D ¹H and ¹³C NMR, HR ESI-MS, IR, and UV spectra.

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Funding

This research was funded by the program STAR 2017, financially supported by Università di Napoli and Compagnia di San Paolo (grant number E62F16001250003). Antonio Evidente is associated with “Istituto di Chimica Biomolecolare del CNR,” Pozzuoli, Italy.