Plocamium hamatum and its monoterpenes: chemical and biological investigations of the tropical marine red alga

The polyhalogenated monoterpene content of six samples of the tropical mari ne red alga Plocamium hamatum, collected from the southern, central and nor thern regions of The Great Barrier Reef, Australia, was assessed. In all bu t two of the samples, the polyhalogenated monoterpene content was shown to differ markedly. In total, eleven previously reported compounds were isolat ed and characterised (1-11). Compound 2 was obtained for the first time as a pure natural product. For compound 4 a single crystal X-ray crystallograp hic analysis was undertaken which established its absolute configuration as (1S,2S,4R,5R,1'E)-2-bromo-1-bromomethyl-1,4-dichloro-5-(2'-chloroethenyl)- 5-methylcyclohexane. Complete and unambiguous H-1 and C-13 NMR data are rep orted for 2 and 4. For 6-8, some prior C-13 NMR assignments are revised. Th e biological activities of compounds 2-8 and 11 were assessed and indicated 4 to have potent antialgal activity towards Chlorella fusca in an agar dif fusion bioassay, as well as being moderately antitubercular and cytotoxic. Compound 6 demonstrated moderate cytotoxicity. (C) 1999 Elsevier Science Lt d. All rights reserved.