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■ 1-Hydroxyethylhalenaquinone: A New Proteasome Inhibitor from the Marine Sponge Xestospongia sp.

Michiko Yamakuma, Hikaru Kato, Kanae Matsuo, Ahmed H. El-Desoky, Tetsuro Kawabata, Fitje Losung, Remy E. P. Mangindaan, Nicole J. de Voogd, Hideyoshi Yokosawa, and Sachiko Tsukamoto*

*Graduate School of Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-hon-machi, Kumamoto 862-0973, Japan

Abstract

A new halenaquinone derivative, 1-hydroxyethylhalenaquinone (1), was isolated from the marine sponge Xestospongia sp. as a proteasome inhibitor together with three known compounds, halenaquinone (2) and 3-ketoadociaquinones A (3) and B (4). 1-Hydroxyethylhalenaquinone (1) was the first halenaquinone derivative containing an alkyl group at the keto-furan C-1 position. Compounds 1 and 2 inhibited the chymotrypsin-like activity of the proteasome with IC50 values of 0.19 and 0.63 μM, respectively, whereas 3 or 4, each containing a thiomorpholine 1,1-dioxide moiety, scarcely inhibited its activity, even at a concentration of 5 μM.