Expanstines A-D: four unusual isoprenoid epoxycyclohexenones generated by Penicillium expansum YJ−15 fermentation and photopromotion
Two new isoprenoid epoxycyclohexenones, expanstines A-B (1-2), and two novel isoprenoid epoxycyclohexenones, expanstines C-D (3-4), featuring an unusual oxetane ring were isolated from Penicillium expansum YJ-15. Their structures were initially investigated in detail by NMR spectroscopy, HRESIMS, XRD and ECD experiments. Expanstines A-D were derived under UV and visible light from 5 and 6, which plausibly underwent a rare intramolecular photoene reaction and a [2+2] Paternò–Büchi photoaddition respectively. Both 3 and 4 exhibited potent antibacterial activities against B. subtilis, with an MIC of 0.25 μg/mL.