Cytotoxic anthrone–cyclopentenone heterodimers from the fungus Penicillium sp. guided by molecular networking

(±)-Penicithrones A–D (1a/1b–4a/4b), four new pairs of anthrone–cyclopentenone heterodimers featuring a unique bridged 6/6/6−5 tetracyclic core skeleton, along with three known compounds (5–7), were isolated from the crude extract of the mangrove-derived fungus Penicillium sp., guided by HSQC-based small molecule accurate recognition technology (SMART 2.0) and LC-MS/MS-based molecular networking. The structures of new compounds were elucidated by extensive spectroscopic data, and the absolute configurations were determined by DP4 + ¹³C NMR calculations and ECD calculations. Compounds 1a/1b–4a/4b showed modest cytotoxicity against three human cancer cell lines HeLa, HCT116 and MCF-7 with IC₅₀ values ranging from 15.95 ± 1.64 to 28.56 ± 2.59 μM.