New crambescidin-type alkaloids from the Indonesian marine sponge Clathria bulbotoxa

Abstract

A crude methanolic extract of the Indonesian sponge <i>Clathria bulbotoxa</i> showed a potent cytotoxic activity against the human epidermoid carcinoma A431 cells. An investigation of the active components led to the isolation of three new compounds named crambescidins 345 (<b>1</b>), 361 (<b>2</b>), and 373 (<b>3</b>), together with the known related metabolites crambescidins 359 (<b>4</b>), 657 (<b>5</b>), and 800 (<b>6</b>). The structures of the compounds were determined by spectroscopic analysis. These compounds <b>1</b>-<b>4</b> that possess a simple pentacyclic guanidine core exhibited moderate cytotoxicity against the A431 cells with the IC₅₀ values of 7.0, 2.5, 0.94, and 3.1 μM, respectively, while the known compounds <b>5</b> and <b>6</b> that possess a long aliphatic side chain were found to be significantly cytotoxic. On the other hand, in an anti-oomycete activity test against the fungus-like plant pathogen <i>Phytophthora capsici</i>, <b>1</b>-<b>4</b> showed a higher activity than that of <b>5</b> and <b>6</b>, suggesting that the long aliphatic side chain plays a significant role for cytotoxicity, but is not effective or suppressive for anti-oomycete activity.

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