Semisynthesis of Mallotus B from Rottlerin: Evaluation of Cytotoxicity and Apoptosis-Inducing Activity

Mallotus B (<b>2d</b>) is a prenylated dimeric phloroglucinol compound isolated from <i>Mallotus philippensis.</i> There have been no reports on the synthesis or biological activity of this compound. In the present paper, a semisynthetic preparation of mallotus B is reported via base-mediated intramolecular rearrangement of rottlerin (<b>1</b>), which is one of the major constituents of <i>M. philippensis</i>. The homodimer “rottlerone” was also formed as one of the products of this base-mediated intramolecular reaction. Rottlerin (<b>1</b>), along with rottlerone (<b>2c</b>) and mallotus B (<b>2d</b>), was evaluated for cytotoxicity against a panel of cancer cell lines including HEPG2, Colo205, MIAPaCa-2, PC-3, and HL-60 cells. Mallotus B (<b>2d</b>) displayed cytotoxicity for MIAPaCa-2 and HL-60 cells with IC<sub>50</sub> values of 9 and 16 μM, respectively. Microscopic studies in HL-60 cells indicated that mallotus B (<b>2d</b>) induces cell cycle arrest at the G1 phase and causes defective cell division. It also induces apoptosis, as evidenced by distinct changes in cell morphology.