Isolation, structural characterisation and evaluation of cytotoxic activity of natural products from selected South African marine red algae
- Authors: Knott, Michael George
- Date: 2012
- Subjects: Marine algae -- South Africa , Red algae -- South Africa , Pharmaceutical chemistry
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3862 , http://hdl.handle.net/10962/d1015460
- Description: The medicinal chemistry of selected marine algae indigenous to South Africa was investigated. Following the isolation and characterisation of a number of new and known compounds, the associated in vitro cytotoxic profiles of these new compounds was investigated. Plocamium maxillosum yielded two new cyclic polyhalogenated monoterpenes which were characterised as 2E-chloromethine-4E-chlorovinyl-4-methyl-5-cyclohexen-1-one (2.1) and 2Z-chloromethine-4E-chlorovinyl-4-methyl-5-cyclohexen-1-one (2.2) on the basis of one and two dimensional NMR spectroscopic data and MS analysis. These compounds were also found to have good cytotoxic activity against breast cancer cell lines. Although these compounds are based on a regular monoterpene skeleton, they represent an uncommon feature not often seen in cyclic halogenated monoterpenes from marine algae. Plocamium robertiae yielded one new cyclic polyhalogenated monoterpene identified as 4,5- dibromo-5-chloromethyl-1-chlorovinyl-2-chloro-methylcyclohexane (2.6) and one known compound called 2,4-dichloro-1-chlorovinyl-1-methylcyclohexane-5-ene or Plocamene D (2.9). Portieria hornemannii was collected from Port Edward in Natal and yielded three new compounds, namely; 3Z-1,6-dibromo-3-(bromomethylidene)-2,7-dichloro-7-methyloctane (3.1), 1E,3Z-1,6-dibromo-3-(bromomethylidene)-7-chloro-7-methyloct-1-ene (3.2), 1Z,3Z- 1,6-dibromo-3-(bromomethylidene)-7-chloro-7-methyloct-1-ene (3.3), and one known compound, namely; 3S,6R-6-bromo-3-(bromomethyl)-3,7-dichloro-7-methyloct-1-ene (3.4). Compounds 3.1 and 3.2 showed no cytotoxic activity against breast cancer cells. Another Portieria hornemannii sample was collected from Noordhoek in the Eastern Cape, it yielded one known compound referred to as 3Z-6-bromo-3-(bromomethylidene)-2,7- dichloro-7-methyloct-1-ene (3.5), as well as one new compound called portieric acid A (3.6) or 5-bromo-2-(bromomethylidene)-6-chloro-6-methylheptanoic acid. Portieric acid A showed slight cytotoxic activity and also represents a new class of compound within the genus Portieria. The isolation of secondary metabolites from the South African red alga, Laurencia glomerata, yielded two known compounds; 7-hydroxylaurene (4.9) and cis-neolaurencenyne (4.12), as well as one chamigrane related compound (4.11). Laurencia flexuosa yielded one known compound called 3Z-bromofucin (4.13). Using 1H NMR, GC and molecular systematics, a novel method for identifying different species of Laurencia was also investigated.
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- Date Issued: 2012
The natural product chemistry of South African Plocamium species
- Authors: Knott, Michael George
- Date: 2003
- Subjects: Marine algae -- South Africa Red algae -- South Africa Green algae -- South Africa Halimeda -- South Africa
- Language: English
- Type: Thesis , Masters , MPharm
- Identifier: vital:3820 , http://hdl.handle.net/10962/d1004920
- Description: The brine shrimp lethality assay was used as a preliminary tool to screen eighteen seaweeds collected from the South African coast. Of the seaweeds tested, the red algae Plocamium corallorhiza and Hypnea rosea, and the green alga Halimeda sp., showed the most potent activity. The chemical investigation of P. corallorhiza resulted in the isolation and structural elucidation of five previously undescribed secondary metabolites, along with three known compounds and four possible artifacts of the extraction process. Standard spectroscopic methods and comparison with known compounds were used to determine the structures of the new metabolites. The new compounds included the linear halogenated monoterpenes 4,8-dibromo-1, 1-dichloro-3,7-dimethyl-2,6-octadiene (99), 4,6-dibromo-l, 1-dichloro-3,7-dimethyl-2,7-octadiene (100), 4,8-dibromo-l, 1,7-trichloro-3,7-dimethyl-2,5-octadiene (101) and 3,4,6,7-tetrachloro-3,7-dimethyl-l-octene (102) and the cyclic monoterpene 5-bromo-5-bromomethyl-I-chlorovinyl-2,4-dichloro-methylcyclohexane (103) while the known compounds were identified as 4-bromo-5-bromomethyl-1chlorovinyl-2,5-dichloro-methylcyclohexane (35), 1,4,8-tribromo-3, 7 -dichloro-3,7-dimethyl-1,5-octadiene (94) and 8-bromo-1,3,4,7-tetrachloro-3,7-dimethyl-1,5-octadiene (96). The four methoxylated compounds (104-107) were presumably formed via a standard substitution reaction between the halogenated monoterpenes 96 and 101 and MeOH, which was used as a component in the extraction solvent. With over 100 000 natural products having been reported, it has become necessary to employ an efficient dereplication strategy to quickly identify known compounds. A simple Gas Chromatography-Mass Spectrometry (GC-MS) method for the efficient physicochemical screening, identification and dereplication of Plocamium metabolites was developed. In this study the crude extracts of P. corallorhiza, P. cornutum and P. maxillosum were screened by GC-MS and the retention times and mass spectral fragmentation patterns of compounds 94, 96, 99 - 107 were used to quickly identify known and new compounds in the crude extracts of P. cornutum and P. maxillosum. This data indicated that compounds 99, 100, 103 were present in both P. corallorhiza and P.cornutum, while compound 102 was found to be present in P. corallorhiza, P. cornutum and P. maxillosum. These studies also indicated that ecotypes and chemotypes are not a significant feature of P. corallorhiza and P. cornutum. Different species of Plocamium (namely: P. corallorhiza, P. cornutum, and P. maxillosum) have very different chemical profiles, and GC may therefore have appreciable taxonomic application in the identification of the different Plocamium spp. which are endemic to South Africa.
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- Date Issued: 2003