Ustusolate A

Chemical investigation of a coculture of the marine-derived fungi Beauveria felina KMM 4639 and Aspergillus carneus KMM 4638 led to the identification of three new drimane-type sesquiterpenes, asperflavinoids B, D and E (2, 4, 5), and nine previously reported related compounds. The structures of these compounds were established using spectroscopic methods and by comparison with known analogues. We also investigated the cytotoxic activity of the isolated compounds against several cancer and normal cell lines. Asperflavinoid C (3) and ustusolate E (9) exerted a significant effect on human breast cancer MCF-7 cell viability, with IC50 values of 10 µM, and induced in caspase-dependent apoptosis and arrest of the MCF-7 cell cycle in the G2/M phase in these cells.

Four new drimane sesquiterpenoids (1-4) and three known ones (5-7) were isolated from the fermentation broth of the mangrove-derived Aspergillus ustus 094102. Compound 5 was further resolved as four purified compounds 5a-5d. By means of extensive spectroscopic and ECD analysis as well as the chemical transformation, their structures were identified as (2R,3R,5S,9R,10S)-2,3,9,11-tetrahydroxydrim-7-en-6-one (ustusol F, 1), (2R,3R,5R,9S,10R)-2,3,11-trihydroxydrim-7-en-6-one (9-deoxyustusol F, 2), (3S,5R,9R,10R)-3,11,12-trihydroxydrim-7-en-6-one (ustusol G, 3), (5S,6R,9S,10S, 11R,2'E,4'E)-(11-dideoxy-11-hydroxystrobilactone A-6-yl)-5-carboxypenta-2,4-dienoate (ustusolate H, 4), ((5S,6R,9S,10S)-strobilactone A-6-yl) (2E,4E)-6,7-dihydroxyocta-2,4-dienoate (ustusolate I, 5), (2'E,4'E;6',7'-erythro)-ustusolate I (5a) and (2'E,4'E;ent-6',7'-erythro)-ustusolate I (5b), (2'E,4'E,6'R,7'R)-ustusolate I (5c) and (2'E,4'E,6'S,7'S)-ustusolate I (5d), (5S,6R,9S,10S,2'E,4'E)-(strobilactone A-6-yl)-5-carboxypenta-2,4-dienoate (ustusolate J, 6), and (2S,5S,9R,10S)-2,9,11-trihydroxydrim-7-en-6-one (ustusol B, 7), respectively. Compound 5 showed antiproliferation against the human tumor cells CAL-62 and MG-63 with the IC50 values of 16.3 and 10.1 µM, respectively.

Bioactivity-guided isolation of Aspergillus ustus led to the discovery of five new drimane sesquiterpenes, named ustusal A, ustusolate F and G, and ustusoic acid A and B, 1-5 respectively. Structural elucidation of these fungal terpenes relied on 1D and 2D NMR techniques, high-resolution mass spectrometry, and chiroptical properties. Their relative configurations were determined by NMR methods, while the absolute configurations were established using comparative analyses of computed and experimental NMR chemical shifts and ECD spectra. The sesquiterpenes exhibited weak activity against the clinically relevant pathogens vancomycin-resistant Enterococcus faecium and multidrug-resistant Staphylococcus aureus; however, the activity of 5 was drastically enhanced when equal amounts of stromemycin (6), a known metabolite coisolated from the same fraction from A. ustus, was added.