The Fungal Endophyte Nigrospora oryzae Produces Quercetin Monoglycosides Previously Known Only from Plants

Abstract

Three quercetin-3-O-glycosides (1–3) were obtained from the endophytic fungus Nigrospora oryzae isolated from leaves of the Nigerian mistletoe Loranthus micranthus. The compounds were unequivocally identified based on their one and two dimensional NMR spectra and on their mass spectra. A fourth flavonoid glycoside (4) was tentatively identified as a luteolin monoglycoside. Comparative HPLC analyses of extracts of the endophyte and of the host plant indicated that compounds (1–3) were present as minor constituents in the extract of the host plant Loranthus micranthus whereas the latter was dominated by different gallic acid and by catechin derivatives that were missing in the endophyte extract. The presence of flavonoid glycosides in a fungal endophyte is remarkable and is unequivocally confirmed here for the first time. So far, compounds (1–3) were only known as commonly occurring plant secondary metabolites. This study adds further evidence to the remarkable plasticity of fungal secondary metabolism which has repeatedly been shown to produce the same compounds as present in plants.