Lissoclinotoxins E and F, novel cytotoxic alkaloids from a Philippine didemnid ascidian

Bioassay-guided fractionation of the MeOH extract from a Philippine didemnid ascidian resulted in the isolation of two new dimeric alkaloids, lissoclinotoxins E (1) and F (2). The polysulfide structures for compounds 1 and 2 were determined by interpretation of spectroscopic data and chemical degradation. Computational chemistry studies suggested that the N-alkyl chains about the tricyclic systems of lissoclinotoxins E and F had trans and cis orientations, respectively. Alkaloids 1 and 2 displayed IC50 values of 2.3 and 1.5 mug/mL, respectively, towards the PTEN-deficient human breast carcinoma cell line, MDA-MB-468. (C) 2003 Elsevier Science Ltd. All rights reserved.