Production of unusual dispiro metabolites in Pestalotiopsis virgatula endophyte cultures: HPLC-SPE-NMR, electronic circular dichroism, and time-dependent density-functional computation study

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Julie Regitze Kesting, Lars Olsen, Dan Stærk, Mysore V Tejesvi, Kukkundoor R Kini, Harishchandra S Prakash, Jerzy W. Jaroszewski

The endophytic fungus Pestalotiopsis virgatula, derived from the plant Terminalia chebula and previously found to produce a large excess of a single metabolite when grown in the minimal M1D medium, was induced to produce a variety of unusual metabolites by growing in potato dextrose broth medium. Analysis of the fermentation medium extract was performed using an HPLC-PDA-MS-SPE-NMR hyphenated system, which led to the identification of a total of eight metabolites (1-8), six of which are new. Most of the metabolites are structurally related and are derivatives of benzo[c]oxepin, rare among natural products. This includes dispiro derivatives 7 and 8 (pestalospiranes A and B), having a novel 1,9,11,18-tetraoxadispiro[6.2.6.2]octadecane skeleton. Relative and absolute configurations of the latter were determined by a combination of NOESY spectroscopy and electronic circular dichroism spectroscopy supported by time-dependent density-functional theory calculations (B3LYP/TZVP level). This work demonstrates that a largely complete structure elucidation of numerous metabolites present in a raw fermentation medium extract can be performed by the HPLC-SPE-NMR technique using only a small amount of the extract, even with unstable metabolites that are difficult to isolate by traditional methods.
Original languageEnglish
JournalJournal of Natural Products
Volume74
Issue number10
Pages (from-to)2206-2215
ISSN0163-3864
DOIs
Publication statusPublished - 26 Sep 2011

ID: 34528049