Novel carbon-bridged citrinin dimers from a volcano ash-derived fungus Penicillium citrinum and their cytotoxic and cell cycle arrest activities

Three novel carbon-bridged citrinin dimers, dicitrinones A–C (1–3), were isolated from a volcano ash-derived fungus Penicillium citrinum. Their structures were elucidated by spectroscopic methods. Dicitrinone A (1) and B (2) are two atropisomeric mixtures, which were verified by both NMR and quantum chemical calculations. Their cytotoxicity against four tumor cell lines (HL-60, MOLT-4, A-549, and BEL-7402) was evaluated by SRB and MTT methods. Dicitrinone B (2) arrested the HL-60 cell cycle at the G2/M phase, which was analyzed using flow cytometry.