Browsing by Author "Said, Sadri Abdullah"

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    Chemical studies of some biologically active soft corals from Tanzanian coast.
    (University of Dar es Salaam, 1994) Said, Sadri Abdullah
    Three biologically active Lobophytum species, L. crassum von Marenzeller (1886), L. rotundum Tixier-Durivault {1957) and L. venustum Tixier-Durivault (1957} and one unidentified Sinularia species were phytochemically investigated. One cembranolide (E,E,E)-6,10,14-trimethyl-3-methylene-3a,4,7,8,11,12,15,15aoctahydrocyclotetradeca[b]furan-2(3H) - one was obtained from L. crassum and L. rotundum. The epoxycembrenoid (E,E,E)-7,8-epoxy-l-isopropyl-4,8,12trimethylcyclotetradeca-1,3,12-triene, which was in a mixture with two ether glycerols, was isolated from L. venustum. The less polar components of L. rotundum and L. venustum yielded large amounts of hexadecyl hexadecanoate while that of L. crassum gave octadecyl hexadecanoate. L. rotundum also afforded "two ether glycerols 1-O-octadecyl-sn-glycerol and 1-fl-octadecyl-2,3-O-dihexadecanoyl-snglycerol. Another glycerol, 1-O-octadecyl-3-O-hexadecanoyl-sn-glycerol, was isolated from an unidentified Sinularia species. 1-O-octadecyl-sn-glycerol was also found in the Sinularia species. All three Lobophytum species were found to consist of mixtures of common marine sterols, cholesterol, ergosterol, gorgosterol, gorgostanol, 24 methylcholesta-5,25-dien-3b-01, ergosta-5,25-dien-3b-o1, ergosta-5,24(28)-dien3b-ol, demethylgorgosterol and demethylgorgostanol and traces of two unidentified sterols. A new sterol, 3b-acetoxy-20,22-epoxy-24-norcholestane, which bears an epoxide moiety in the side chain, was obtained from L. rotundum. All compounds were identified on the basis of their 1H- and 13C-NMR, COSY and NOESY spectral data. The mixtures of sterols were identified by comparison of their mass spectral data (which were obtained by GC-MS) with those reported in the literature. The cembranolide (E,E,E)-6,10,14-trimethyl-3-methylene-3a,4,7,8,11,12,15,15a- ctahydrocyclotetradeca[b]furan-2(3H)-one was found to be cytotoxic, with an IC50 value of 1.15 µg/ml. It was also active against the multidrug resistant Kl and chloroquine sensitive NF54 strains of Plasmodium falciparum malaria parasite in vitro (IC50 values of 2.5 and 1.8 µg/ml respectively for the two strains). The epoxysterol might be a biogenetic precursor of the side chain alkylated sterols, which were found in the same soft coral, since the epoxide system is very reactive and it may undergo a variety of reactions, including C-alkylation, to yield the side chain modified sterols.