title: Reassessing the structure of pyranonigrin.
abstract: Fermentation extracts of the marine fungus Aspergillus niger LL-LV3020 were found to have relevant activity in a number of assays. Chemical screening of the extracts revealed that this organism produced numerous secondary metabolites in addition to its principal metabolite, citric acid. The compound with the most significant UV peak was isolated and its structure elucidated. Physical data suggested that this compound is identical with pyranonigrin A (1); however, our structure elucidation led to a different assignment than previously reported. On the basis of analysis of all data, we propose a correction to the structure of pyranonigrin A. Its absolute configuration was determined by electronic circular dichroism measurements in comparison with theoretical values calculated via ab initio time-dependent density functional theory and assigned as (7R)-3,7-dihydroxy-2-[(1E)-prop-1-enyl]-6,7-dihydropyrano[2,3-c]pyrrole-4,5-dione.
authors.affiliation: Department of Natural Products, Chemical and Screening Sciences, Wyeth Research, 401 North Middletown Road, Pearl River, New York 10965, USA. schling@wyeth.com
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schlingmann
authors.forename: Tohru
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Haiyin
authors.initials: H
authors.lastname: He
authors.forename: Ramunas
authors.initials: R
authors.lastname: Bigelis
authors.forename: Hui Y
authors.initials: HY
authors.lastname: Yang
authors.forename: Frank E
authors.initials: FE
authors.lastname: Koehn
authors.forename: Guy T
authors.initials: GT
authors.lastname: Carter
authors.forename: Nina
authors.initials: N
authors.lastname: Berova
mesh_terms: D001234:Aspergillus niger / Q000737:chemistry*; D019343:Citric Acid / Q000378:metabolism; D018360:Crystallography, X-Ray; D008968:Molecular Conformation; D015394:Molecular Structure; D011753:Pyrones / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D011753:Pyrones; D011758:Pyrroles; C522144:pyranonigrin A; D019343:Citric Acid