Natural products from tropical and temperate marine algae

Following surveys of seaweeds in Oregon and the Caribbean, four algal species were selected for study on the basis of their crude extract biological activity or thin-layer chromatographic characteristics. Extracts were fractionated by normal phase chromatography, including high performance liquid chromatography (HPLC). Derivatives (methyl esters, acetates, and benzoates) of natural products were produced to facilitate isolation or structure elucidation efforts. Structure proofs utilized high-field nuclear magnetic resonance (NMR) spectroscopy, including hetero- and homo-nuclear two-dimensional experiments. Infrared and ultraviolet spectra, optical rotations, mass spectra, and circular dichroic spectroscopy were also employed. The Puerto Rican red alga Murrayella periclados was found to contain (12S)-hydroxyeicosapentaenoic and (12S)-hydroxyeicosatetraenoic acids, two mammalian autacoids for which new biological activities are reported. Further eicosanoid metabolism was demonstrated by the isolation of (6E)-leukotriene B₄ and two diastereomers each of the insulin-release mediators hepoxilin B₃ and B₄. The Oregon green alga Acrosiphonia coalita also was found to contain novel fatty acid-derived substances. Some of these contain an unprecedented structural feature, a conjugated trienal in which the aldehyde moiety branches off from the fatty acid chain. Exciton chirality studies of benzoate derivatives indicate that the alga introduces oxygenation in the 9R, 13S, and 16S positions on precursor polyunsaturated fatty acid chains. The Oregon red alga Laurencia spectabilis was found to produce an equilibrium mixture of (±)-2-hydroxy-2-methyldihydrofuran-3-one and 5-hydroxy- 2,3-pentanedione, which dimerizes on silica gel to produce spiro-bis-pinnaketal, a compound which was previously reported from L. pinnatifida and is probably an artifact of isolation. The Oregon red alga Prionitis lanceolata displays high levels of apparent tryptophan metabolism. Never before isolated from a plant or marine source, 3- (hydroxyacetyl)indole, active at 10⁻¹⁰ M in the lettuce-seedling root elongation assay, was isolated in 0.07% yield along with indole-3-carboxaldehyde (0.5%) and indole-3-carboxylate (0.04% )