3rd Portuguese Meeting on Medicinal Chemistry and 1st Portuguese-Spanish-Brazilian Meeting on Medicinal Chemistry, Aveiro, 28-30 Novembro 2012.New drugs from natural sources have been targets of the drug discovery program and some bioactive compounds from macroalgae such as sulfated polysaccharides, steroids and diterpens have found their applications in the pharmaceutical industry.[1,2] Consequently, we have investigated the chemical composition and the in vitro antitumor potential of the metabolites isolated from the macroalga Ulva rigida, collected from the Azorean coast, an environmentally healthy habitat with a high level of biodiversity. We hereby describe isolation of isofucosterol (1) and 7(E)-3ẞ-hidroxy-5α, 6α-epoxymegastigmane (2) from the methanol extract of Ulva rigida, collected in May of 2011 in the Sea of St Miguel Island - Azores archipelago. The process of isolation of these metabolites involved chlorophylls elimination by the method previously described[3] and fractionation by column chromatography. The structures of 1 and 2 were established by 1D and 2D NMR spectral analysis and specific rotation as well as comparison of their spectral data with those described in the literature.[4,5] Compounds 1 and 2 were evaluated for their capacity to inhibit the in vitro growth of three human cancer cell lines: MCF-7 (breast adenocarcinoma), NCI-H460 (non-small cell lung cancer) and A375-C5 (human skin cell line), using the protein binding dye SRB method. The results showed that compound 1 exhibited only a weak activity against MCF-7 (GI50 = 122.2 ± 17.9 μM), NCI-H460 (GI50 = 128.4 ± 32.4 μM), A375-C5 (GI50 = 119.2 ± 28.9 μM), while compound 2 was inactive against all the three cell lines (GI50 >200 μM).This work was financially supported by the project, Bioactive products in marine algae of Azores (PTDC/MAR/100482/2008) from Fundação para a Ciência e a Tecnologia (FCT). Madalena Silva thanks FCT for the young researcher scholarship under PTDC/MAR/100482/2008 project
