New rare atropisomers: structure elucidation, absolute configuration and antimicrobial activity

Fungi are very known to produce polyketides, which are structurally a very diverse family of natural products with interesting biological activities and pharmacological properties. We report in this study the chemical investigation of two endophytic fungi, Stemphylium globuliferum and Talaromyces wortmanii. Several rare new atropisomers were isolated and identified, including homo- and heterodimeric bisanthraquinones. The structure of isolated compounds were determined on the basis of one- and two-dimensional NMR spectroscopy and mass spectrometry. The absolute stereochemistry of the new compounds was established by means of TDDFT ECD calculations. Furthermore, the isolated compounds exhibited antibacterial activity against multi drug resistant strains of Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecium and Enterococcus cloacae. In addition, the anti-fungal activity of the isolated compounds was measured against drug resistant strains of Aspergillus fumigatus, Aspergillus faecalis, Candida albicans and Candida krusei. Interestingly, among the compounds isolated, only the new altersolanol N, tetrahydroaltersolanol B and altersolanol C were active against HV2 and HV8 human viruses.

Keywords: Endophytes, Atropisomers, Spectroscopy, CD calculation, Antimicrobial activity