Auslactones A-E, austalide meroterpenoids from Aspergillus ustus NRRL 275

Five new austalide meroterpenoids, named auslactones A - E (1-5), one new natural product (6), together with ten known analogues (7-16), were isolated from the fungus Aspergillus ustus NRRL 275. Auslactones A - B (1-2) represent a class of austalides containing 5/6/6/6/6/5 hexacyclic ring with a hydroxymethyl group at C-15. Auslactones C - D (3-4) enrich the type of 5/6/6/6/5/6/5 heptacyclic austalides. Auslactone E (5) contains 5/6/6/6 tetracyclic ring system. Meanwhile, the NMR data of auslactone F (6) were reported for the first time. Their structures were elucidated by extensive spectroscopic analysis. The absolute configuration of compound 1 was established by single-crystal X-ray diffraction, whereas those for the others were established by circular dichroism (CD) data analysis. No cytotoxic or immunosuppressive activity was found for compounds 1-6.