Spiroaspertrione A, a Bridged Spirocyclic Meroterpenoid, as a Potent Potentiator of Oxacillin against Methicillin-Resistant Staphylococcus aureus from Aspergillus sp TJ23

Bioassay-guided isolation of cultures of Aspergillus sp. TJ23 yielded a novel terpene-polyketide hybrid spiromeroterpenoid, spiroaspertrione A (1), bearing a unique spiro[bicydo[3.2.2]nonane-2,1'-cyclohexane] carbocydic skeleton, and a new biointermediate, andiconin B (2). Their structures and absolute configurations were elucidated by spectroscopic analyses, single-crystal X-ray diffraction, and electronic circular dichroism calculations. Compound 1 demonstrated potent resensitization of oxacillin against methicillin-resistant Staphylococcus aureus by lowering the oxacillin minimal inhibitory concentration up to 32-fold from 32 to 1 mu g/mL.