Gabriele M. König

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 marine red alga Plocamium hamatum, collected from the southern, central and northern regions of The Great Barrier Reef, Australia, was assessed. In all but two of the samples, the polyhalogenated monoterpene content was shown to differ markedly. In total, eleven previously reported compounds were isolated 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 crystallographic analysis was undertaken which established its absolute configuration as (1S,2S,4R,5R,1E)-2-bromo-1- bromomethyl-1,4-dichloro-5-(2-chloroethenyl)-5-methylcyclohexa ne. Complete and unambiguous 1H and 13C NMR data are reported for 2 and 4. For 6-8, some prior 13C NMR assignments are revised. The biological activities of compounds 2-8 and 11 were assessed and indicated 4 to have potent antialgal activity towards Chlorella fusca in an agar diffusion bioassay, as well as being moderately antitubercular and cytotoxic. Compound 6 demonstrated moderate cytotoxicity.

Hierridin B and 2,4-dimethoxy-6-heptadecyl-phenol, secondary metabolites from the cyanobacterium Phormidium ectocarpi with antiplasmodial activity

Bioassay guided fractionation of the lipophilic extract of the marine cyanobacterium Phormidium ectocarpi yielded a new natural product hierridin B and the previously described compound 2,4-dimethoxy-6-heptadecyl-phenol. Both structures were secured by extensive spectroscopic analysis (1D and 2D NMR, MS, GC-MS, IR). The isolate (mixture) showed antiplasmodial activity towards Plasmodium falciparum.

Manzacidin D: An unprecedented secondary metabolite from the “living fossil” sponge Astrosclera willeyana☆

The methanol extract of Astrosclera willeyana was found to contain the unprecedented natural product manzacidin D (1), norzooanemonin (2), and trigonelline (3).

1H and 13C‐NMR and biological activity investigations of four lichen‐derived compounds

The lichen-derived natural products, atranorin (1), hopane-6α, 22-diol (2), usnic acid (3), and vulpinic acid (4) were analysed by both one and two-dimensional (1H, 13C)-NMR. Experiments employed included COSY, NOESY, XHCO, HMQC and HMBC. For 1 and 2, fully assigned proton NMR data are reported for the first time; the reassigned 13C NMR data for both 1 and 2 are also reported. For 3, cross-peaks were observed in the HMBC spectrum that suggest that CH long-range coupling through H bonds is occurring. Biological activity investigations of each compound indicated hopane-6α, 22-diol (2) to have anti-tubercular activity (MIC 8u2005µg/mL) and usnic acid (3) to be very weakly cytotoxic (ED50 13u2005µg/mL). Copyright

Four diterpene isonitriles from the sponge Cymbastela hooperi

The low-temperature X-ray structures of four isomeric diterpene isonitriles, C21H31N, obtained from the sponge Cymbastela hooperi, are reported. These are the tetracyclic compounds, (1S*,3S*,4R*,7S*,8S*,12S*,13S*)-7-isocyanocycloamphilect-11(20)-ene (alternative name: 1,4,7,7-tetramethyl-1,2,3,3a,4,5,5a,6,7,9,10,10a,10b,10c-tetradecahydropyrenyl 1-isocyanide) and (1S*,3S*,4R*,7S*,8S*,11R*,12R*,13S*,20S*)-7-isocyanoisocycloamphilect-14-ene (alternative name: 1,4,7,8-tetramethyl-1,2,3,3a,4,5,5a,8,8a,9,10,10a,10b,10c-tetradecahydropyrenyl 1-isocyanide), and the tricyclic compounds, (1S*,3S*,4R*,7S*,8S*,12S*,13S*)-7-isocyanoamphilecta-11(20), 15-diene [alternative name: 1,4-dimethyl-7-methylene-6-(2-methyl-2-propenyl)perhydro-1H-phenalenyl 1-isocyanide] and (1R*,3S*,4R*,7S*,8S*,13R*)-7-isocyanoamphilecta-11,14-diene [alternative name: 1,4,7-trimethyl-6-(2-methyl-1-propenyl)-2,3,3a,4,5,6,8,9,9a,9b-decahydro- 1H-phenalenyl 1-isocyanide]. All of the structures exhibit trans-fused ring systems.

Pulsed field gradient spectroscopy (PFGS): application to the structure elucidation of (+)-(10S)-10-bromo-β-chamigrene†

The structure of the new natural product (+)-(10S)-10-bromo-β-chamigrene (1) was determined using both two-dimensional nuclear magnetic resonance pulsed field gradient spectroscopy (2D-NMR PFGS) and conventional phase cycled methodologies. A discussion of the advantages of PFGS 2D-NMR over conventional phase cycled methodologies, as well as a brief outline of the hard- and soft-ware requirements to enable the PFGS experiments employed to be performed, is given.