Article pubs.acs.org/jnp
Terphenyl Derivatives from Allantophomopsis lycopodina Lars Andernach,† Louis P. Sandjo,†,‡ Johannes C. Liermann,† Ricardo Schlam ̈ ann,§ Christian Richter,⊥ Jan-Peter Ferner,⊥ Harald Schwalbe,⊥ Anja Schüffler,§ Eckhard Thines,§,∥ and Till Opatz*,† †
Institute of Organic Chemistry, Johannes Gutenberg-University, Duesbergweg 10−14, D-55128 Mainz, Germany Departamento de Ciências Farmacêuticas, Centro de Ciências da Saúde, Bloco J/K, Universidade Federal de Santa Catarina, Florianópolis 88040-900, SC, Brazil § Institut für Biotechnologie und Wirkstoff-Forschung gGmbH, Erwin-Schrödinger-Straße 56, D-67663 Kaiserslautern, Germany ⊥ Institute of Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-University Frankfurt, Max-von-Laue-Straße 7, D-60438 Frankfurt am Main, Germany ∥ Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-University Mainz, Johann-Joachim-Becherweg 15, 55128 Mainz, Germany ‡
S Supporting Information *
ABSTRACT: Three secondary fungal metabolites 1−3 with a benzo[b]naphtho[2,1-d]furan skeleton were isolated from submerged cultures of the ascomycete Allantophomopsis lycopodina. The NMR-based structure elucidation was challenging due to a low H/C ratio of only 0.64 and 0.68, respectively. NMR measurements in two different solvents and the use of NMR experiments such as HSQC-TOCSY and LRHSQMBC proved to be helpful in this respect. The proposed structures obtained from the comprehensive analysis of the NMR data were verified by comparison of recorded and computed NMR chemical shifts from quantum chemical calculations of several constitutional isomers and were further analyzed with the aid of the DP4 and DP4+ probabilities. he first natural p-terphenyl, polyporic acid, was described as early as 1877.1 Derivatives of terphenyl quinone pigments were isolated from basidomycetes, such as Tapinella atrotomentosa (= Paxillus atrotomentosus),2,3 Omphalotus subilludens (= Clitocybe subilludens),4 and Punctularia atropurpurascens,5 as well as from ascomycetes, e.g., Ascocoryne sarcoides6 and Aspergillus candidus.7 In 2009, allantofuranone, a fungistatic secondary metabolite, was isolated from cultures of the ascomycete Allantophomopsis lycopodina IBWF58B-05A.8 Feeding experiments were used to demonstrate that polyporic acid is the biosynthetic precursor of allantofuranone.9 In addition, the isolation of 5-hydroxy-3,4,7-triphenyl-2,6-benzo[b]furandione gave evidence that this species is able to produce terphenyl quinone derivatives.9 Allantophomopsis lycopodina is described as a plant pathogen on cranberries 10 and lingonberries.11 In order to investigate phytotoxic secondary metabolites, the fungus IBWF58B-05A was cultured in different media. Although no phytotoxic metabolites were identified, A. lycopodina IBWF58B-05A produced several compounds in the Raulin-Thom medium that were not produced in the other tested media. Three of these compounds were isolated and characterized. The structure elucidation of compounds with a low H/Cratio by NMR spectroscopy can be challenging.12−16 In many of these cases proton-detected heteronuclear experiments such
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as HMBC will not be able to reveal enough correlations to unequivocally establish a proposal for the structure. This problem can be addressed by carbon-detected homonuclear experiments such as 2D-INADEQUATE.17−20 However, such experiments are extremely time-consuming and even with stateof-the-art cryogenic 5 mm probes still not feasible for small amounts (
