AUTHOR=Shi Lixin , Han Li , Zhao Zeyu , Li Qi , Wang Yanduo , Ding Gang , Xing Xiaoke 

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

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1037292

DOI=10.3389/fmicb.2022.1037292

ISSN=1664-302X

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