Conjugated Polyene Ketones From the Marine Sponge Clathria (Thalysias) Reinwardti (Vosmaer, 1880) and Their Cytotoxic Activity

Abstract

Five conjugated polyene ketones (1-5) were isolated from the methanol extract of the marine sponge Clathria (Thalysias) reinwardti (Vosmaer, 1880) living in the coastal waters of Vietnam. Their structures were determined to be 8-(2′,3′,4′-trimethylphenyl)-6-methyl-oct-3(E),5(E),7(E)-trien-2-one (1), 13-apoastaxanthinone (2), 9-apoastaxanthinone (3), 2,3-dehydro-4-oxo-β-ionone (4), and 4-(2′,3′,4′-trimethylphenyl)-but-3(E)-en-2-one (5), by extensive analysis of high-resolution electron spray ionization mass spectrum (HR-ESI-MS), one-dimensional, and two-dimensional (2D) nuclear magnetic resonance (NMR) spectra, as well as by comparison of the spectral data with those reported in the literature. Compound 1 was new, compounds 2 to 4 were isolated from nature for the first time, and the chemical structure as well as the NMR assignments, of 5 were indicated by 2D NMR for the first time. Additionally, compound 5 exhibited cytotoxic activity against the human cancer cells SK-LU-1, SK-Mel-2, MCF-7, and Hep-G2 with half-minimal inhibitory concentration (IC50) values of 15.12 ± 3.43, 17.41 ± 2.83, 33.12 ± 3.39, and 34.38 ± 3.52 µM, respectively, but displayed only a weak cytotoxic effect on the normal HEK-239A cells (IC50 64.67 ± 3.67 µM). Compound 5 also significantly increased Caspase-3 activity in SK-LU-1 cells at concentrations of 10, 15, and 20 µM.