Furanones and Anthranilic Acid Derivatives from the Endophytic Fungus Dendrothyrium variisporum

Abstract

Extracts from an endophytic fungus isolated from the roots of the Algerian plant Globularia alypum showed prominent antimicrobial activity in a screening for novel antibiotics. The producer organism was identified as Dendrothyrium variisporum by means of morphological studies and molecular phylogenetic methods. Studies on the secondary metabolite production of this strain in various culture media revealed that the major components from shake flasks were massarilactones D (1) and H (2) as well as two new furanone derivatives for which we propose the trivial names (5S)-cis-gregatin B (3) and graminin D (4). Scale-up of the fermentation in a 10 L bioreactor yielded massarilactone D and several further metabolites. Among those were three new anthranilic acid derivatives (5-7), two known anthranilic acid analogues (8 and 9) and three cyclopeptides (10-12). Their structures were elucidated on the basis of extensive spectroscopic analysis (1D- and 2D-NMR), high-resolution mass spectrometry (HRESIMS), and the application of the modified Mosher's method. The isolated metabolites were tested for antimicrobial and cytotoxic activities against various bacteria, fungi, and two mammalian cell lines. The new Metabolite 5 and Compound 9 exhibited antimicrobial activity while Compound 9 showed cytotoxicity activity against KB3.1 cells.

Keywords: Dendrothyrium variisporum; Montagnulaceae; anthranilic acid derivatives; antimicrobial activity; cytotoxicity; fermentation; furancarboxylic acid derivatives.

Figure 1

Structures of secondary metabolites isolated from Dendrothyrium variisporum.

Figure 2

Selected HMBC correlations for Compounds 3 and 4.

Figure 3

ECD spectra of Compounds 3 and 4 in ethanol.

Figure 4

Δδ^SR values (ppm) for the C-4′′ MTPA esters of Compound 4.

Figure 5

Selected HMBC correlations for Compounds 5–7.