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Cytotoxic Isomalabaricane Derivatives and a Monocyclic Triterpene Glycoside from the Sponge Rhabdastrella globostellata

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posted on 24.09.2010, 00:00 authored by Miyabi Hirashima, Kazuomi Tsuda, Toshiyuki Hamada, Hiroaki Okamura, Tatsuhiko Furukawa, Shin-ichi Akiyama, Yusuke Tajitsu, Ryuji Ikeda, Masaharu Komatsu, Matsumi Doe, Yoshiki Morimoto, Motoo Shiro, Rob W. M. van Soest, Kaoru Takemura, Tetsuo Iwagawa
Seven new isomalabaricane derivatives, rhabdastins A−G (17), and a new monocyclic triterpene glycoside, rhabdastoside A (8), have been isolated from the methanol extract of the sponge Rhabdastrella globostellata, collected at Amami-oshima, Japan. Three of them were isolated as their corresponding methyl esters, rhabdastins A−D (13). Their structures were determined on the basis of spectroscopic and X-ray diffraction analyses. The isolated compounds were evaluated for their cytotoxicity against the proliferation of promyelocytic leukemia HL-60 cells. Compounds 4, 5, 7, and 11, possessing a cyclopentane side chain, exhibited weak activity, with IC50 values of 21, 29, 44, and 11 μM, respectively, while compounds 1, 2, and 3, with a 2-substituted-propanoate side chain, were inactive at 100 μM. In addition, the mechanism of cytotoxicity of compounds 4 and 5 was investigated.