Alkaloids from a deep ocean sediment-derived fungus Penicillium sp. and their antitumor activities.

Four new alkaloids, including two new meleagrin analogs, meleagrin D (1) and E (2), and two new diketopiperazines, roquefortine H (3) and I (4), were isolated from a deep ocean sediment-derived fungus Penicillium sp. Meleagrin D (1) and E (2) possess unprecedented acetate-mevalonate-derived side chains on the imidazole moiety. These new meleagrins showed weak cytotoxicity against the A-549 cell line, whereas meleagrin B (5) and meleagrin (6), which were isolated previously from the same strain, induced HL-60 cell apoptosis or arrested the cell cycle through G(2)/M phase, respectively. The results indicate that the distinct substitutions on the imidazole ring significantly influence the cytotoxicity of the meleagrin alkaloids.