title: Production of unusual dispiro metabolites in Pestalotiopsis virgatula endophyte cultures: HPLC-SPE-NMR, electronic circular dichroism, and time-dependent density-functional computation study.
abstract: 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.
authors.affiliation: Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
authors.forename: Julie R
authors.initials: JR
authors.lastname: Kesting
authors.forename: Lars
authors.initials: L
authors.lastname: Olsen
authors.forename: Dan
authors.initials: D
authors.lastname: Staerk
authors.forename: Mysore V
authors.initials: MV
authors.lastname: Tejesvi
authors.forename: Kukkundoor R
authors.initials: KR
authors.lastname: Kini
authors.forename: Harishchandra S
authors.initials: HS
authors.lastname: Prakash
authors.forename: Jerzy W
authors.initials: JW
authors.lastname: Jaroszewski
mesh_terms: D001584:Benzoxepins / Q000737:chemistry / Q000302:isolation & purification*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002942:Circular Dichroism / Q000379:methods*; D060026:Endophytes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015394:Molecular Structure; D013141:Spiro Compounds / Q000737:chemistry / Q000302:isolation & purification*; D029766:Terminalia / Q000382:microbiology; D013997:Time Factors
chemical_list: D001584:Benzoxepins; D013141:Spiro Compounds; C569077:pestalospirane A; C569078:pestalospirane B