Furanoids from the Gymnadenia conopsea (Orchidaceae) seed germination supporting fungus Ceratobasidium sp. (GS2)

Five furanoids including a new analog ( S )-1,4-di(furan-2-yl)-2-hydroxybutane-1,4-dione ( 1 ) together with four known ones, rhizosolaniol ( 2 ), 5-hydroxymethylfurfural ( 3 ), 2-furoic acid ( 4 ) and (2-furyl) oxoacetamide ( 5 ), were isolated from the fungal strain Ceratobasidium sp. (GS2) inducing seed germination of the endangered medicinal plant Gymnadenia conopsea of Orchidaceae. The structure of new furanoid 1 was determined mainly based on HR-ESI-MS and NMR spectral data. Modified Mosher’s reactions were used to establish the stereochemistry of the hydroxyl group in 1 , which was not stable in Mosher’s reagents and transformed into four analogs 6 – 9 . These degraded products ( 6 – 9 ) were elucidated based on UPLC-Q-TOF-MS/MS analysis, and compound 8 was further isolated from the degraded mixture and its structure was characterized through NMR experiments. Therefore, the absolute configuration of compound 1 was determined by electronic circular dichroism combined with quantum-chemical calculations adopting time-dependent density functional theory. Compounds ( 1 – 5 ), and 8 showed weak antioxidant activities, and compounds ( 2 – 4 ) displayed phytotoxicity on punctured detached green foxtail leaves. In addition, compounds 3 and 4 strongly showed inhibition activities on the seed germination of G. conopsea . This was the first chemical investigation of the symbiotic fungus of G. conopsea .