Structurally diverse secondary metabolites from the dung-inhabiting fungus Botryotrichum murorum

Abstract

Abstract A combination of confidence-aware MS/MS-based metabolomics and conventional chemical screening approaches was employed to investigate the metabolome of Botryotrichum murorum DSM 113281, isolated from tortoise dung. The metabolomic survey revealed a high degree of chemical diversity; however, low production rates necessitated large-scale solid-state cultivation to purify the major constituents. This approach led to the discovery of tortoisellide A ( 1 ), which features a rare polyketide γ-lactol scaffold, an unprecedented thio-substituted analogue 2 of the 14-membered bis-macrolactone antibiotic grahamimycin A, alongside the known sesquiterpenoid eremophilane cryptosphaerolide ( 3 ) and isocochliodinol ( 4 ). All planar structures were elucidated by HR-MS and NMR analysis. Tortoisellide A ( 1 ) displayed pronounced tautomerism at its hemiacetal carbon C–23, manifesting in the duplication of most NMR signals. Mosher ester analysis supported the assignment of the 2’ S configuration of compound 2 , while the configurations at C–2 and C–8 were tentatively assigned by analogy to the natural (−)-grahamimycin A1. The previously unassigned side-chain configuration of 3 was determined as 17 S , 19 S , 21 S by NMR chemical shift and J -based configurational analyses (Murata’s method) supported by computational modeling. Compounds showed varying degrees of cytotoxicity against mammalian cell lines, with isocochliodinol being most active displaying potency in the nanomolar range. The metabolite diversity of B. murorum broadens the chemical repertoire of coprophilous fungi and knowledge on the diversification of secondary metabolism in the Sordariales.