Anthraquinones and naphthopyrones from the marine echinoderm Comanthus sp.

A detailed analysis of a Philippine specimen of the marine echinoderm Comanthus sp. yielded fifteen compounds including four anthraquinones identified as 1'-deoxyrhodoptilometrin (1) along with its 6-O-sulfate derivative (3), and rhodoptilometrin (2) with its 6-O-sulfate derivative (4). In addition five naphthpyrones including comaparvin (5), 6-methoxycomaparvin (6), 6-methoxycomaparvin-5-methylether (7), 6-methoxycomaparvin-5-methylether-8-O-sulfate (8), and 6-hydroxycomaparvin-8-O-sulfate (9) were likewise isolated and identified. Further compounds include steroids and a nucleoside derivative. The structures of the isolated compounds were unambiguously elucidated based on HRESIMS analysis, 1D and 2D NMR, and by comparison with the literature. For compounds 2 and 4 the absolute configurations were identified for the first time using the Mosher reaction. Both compounds are (S)-(-) enantiomers. All isolated compounds were evaluated for their cytotoxic activities against cancer cells using the (MTT) assay and compared to the well known marine cancer drug candidate kahalalide F (EC₅₀=6.3 µg/mL). 1'-Deoxyrhodoptilometrine (1) and an unseparable mixture of comaparvin (5) and 6-methoxycomaparvin (6) exhibited pronounced cytotoxicity against mouse lymphoma L5178Y cells with EC₅₀ values of 2.3 and 5.2 µg/mL, respectively.