Chemical investigation of the Thai sponge Hyrtios gumminae collected from Similan Island in the Andaman Sea, Thailand, yielded four new sesterterpenoids, similan A (1), 12beta,20-dihydroxy-16beta-acetoxy-17-scalaren-19,20-olide (2), 12beta-acetoxy-20-hydroxy-17-scalaren-19,20-olide (3), and 12beta,16alpha,20-trihydroxy-17-scalaren-19,20-olide (4), together with seven known compounds. The structures of these new compounds were elucidated on the basis of their spectroscopic data and chemical transformations. Some of the isolated compounds were tested for their cytotoxic activity.

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Four new mammea coumarins, mammea E/BA cyclo D (1), mammea E/BC cyclo D (2), mammea E/BD cyclo D (3), and mammea E/AC cyclo D (4), were isolated from the flowers of Mammea siamensis, along with six known coumarins. Extensive 1D and 2D NMR experiments and other spectroscopic studies, as well as chemical transformations, were employed to determine the structures of 1-4.

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