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Bridged Epipolythiodiketopiperazines from Penicillium raciborskii, an Endophytic Fungus of Rhododendron tomentosum Harmaja

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journal contribution
posted on 08.04.2016, 13:34 by Marena Kajula, Joshua M. Ward, Ari Turpeinen, Mysore V. Tejesvi, Juho Hokkanen, Ari Tolonen, Heikki Häkkänen, Pere Picart, Janne Ihalainen, Hans-Georg Sahl, Anna Maria Pirttilä, Sampo Mattila
Three new epithiodiketopiperazine natural products [outovirin A (1), outovirin B (2), and outovirin C (3)] resembling the antifungal natural product gliovirin have been identified in extracts of Penicillium raciborskii, an endophytic fungus isolated from Rhododendron tomentosum. The compounds are unusual for their class in that they possess sulfide bridges between α- and β-carbons rather than the typical α–α bridging. To our knowledge, outovirin A represents the first reported naturally produced epimonothio­diketopiperazine, and antifungal outovirin C is the first reported trisulfide gliovirin-like compound. This report describes the identification and structural elucidation of the compounds by LC-MS/MS and NMR.