- This thesis is an account of investigation on the natural products deriving
from various marine algae and has resulted in the discovery of eleven novel
bioactive metabolites. Isolation and characterization of these new molecules were
carried out using different chromatographic techniques and by analyses of different
spectroscopic data, respectively.
Using bioassay guided fractionation (brine shrimp toxicity assay), I isolated
and identified five new, biologically active compounds [2β,3α-epitaondiol,
flabellinol, flabellinone, stypoaldehyde and stypohydroperoxide], together with five
known compounds [2-geranylgeranyl-6-methyl-1, 4-benzoquinone, (-) epistypodiol,
(-) stypoldione, fucoxanthin and iditol] from the marine brown alga Stypopodium
flabelliforme, collected from Papua New Guinea. All of the new compounds were
found to have cytotoxic activity (EC₅₀ ranges from 0.8-10 μg/ml) in human lung
cancer (NCI-H460). 2β,3α-epitaondiol and flabellinol exhibited strong sodium
channel blocking activity (EC₅₀=0.3 and 0.9 μg/ml, respectively).
As a result of efforts to identify bioactive agents from marine algae, I have
isolated and identified one new halogenated monoterpene [(-)-(5E,7Z)-3,4,8-
trichloro-7-dichloromethyl-3-methyl-1,5,7-octatriene] in addition to another three
known halogenated monoterpene compounds from the red alga Plocamium
cartilagineum collected from the eastern coast of South Africa. [(-)-(5E,7Z)-3,4,8-
trichloro-7-dichloromethyl-3-methyl-1,5,7-octatriene] was found to be active as a
cytotoxic agent in human lung cancer (NCI-H460) and mouse neuro-2a cell lines
(EC₅₀ 4 μg/ml).
As part of continued search for bioactive secondary metabolites from
marine sources using a bioassay guided fractionation approach (anti-trypanosome
activity), I examined the organic extract of a Papua New Guinean collection of the
green alga Udotea orientalis growing on a coral wall and collected in September
1998. Successive HPLC separations resulted in the isolation of three new
compounds; (+) curcuepoxide A, (+) curcuepoxide B and (+)-l0α-hydroxycurcudiol.
In addition I isolated four known compounds; (+)-10β-
hydroxycurcudiol, (+) curcuphenol, (+) curcudiol and (+) curcudiol-10-one.
A bioassay guided investigation approach (anti-Sirt2) of a Lyngbya
majuscula collection from Key West Florida, led to the discovery of two novel
bioactive natural products [(+)-malyngamide X and one cyclic depsipeptide, (+)-floridamide]. The new cyclic depsipeptide, (+)-floridamide contains four amino
acids units beside the unique unit, 2,2-dimethyl-3-hydroxyoctanoic acid (Dhoaa).