Victoria L. Webb

Polyketide assembly lines of uncultivated sponge symbionts from structure-based gene targeting

There is increasing evidence that uncultivated bacterial symbionts are the true producers of numerous bioactive compounds isolated from marine sponges. The localization and heterologous expression of biosynthetic genes could clarify this issue and provide sustainable supplies for a wide range of pharmaceuticals. However, identification of genes in the usually highly complex symbiont communities remains a challenging task. For polyketides, one of the most important groups of sponge-derived drug candidates, we have developed a general strategy that allows one to rapidly access biosynthetic gene clusters based on chemical moieties. Using this method, we targeted polyketide synthase genes from two different sponge metagenomes. We have obtained from a sponge-bacterial association a complete pathway for the rare and potent antitumor agent psymberin from Psammocinia aff. bulbosa. The data support the symbiont hypothesis and provide insights into natural product evolution in previously inaccessible bacteria.

Didemnidines A and B, Indole Spermidine Alkaloids from the New Zealand Ascidian Didemnum sp.

Two new indole spermidine alkaloids, didemnidines A (1) and B (2), have been isolated from the New Zealand ascidian Didemnum sp. The structures of the metabolites, determined by analysis of 2D NMR spectra and confirmed via synthesis, embody an indole-3-glyoxylamide moiety linked to the N(1) position of spermidine, the latter motif being particularly rare among marine natural products. Didemnidine B and a synthetic precursor exhibited mild in vitro growth inhibition of Plasmodium falciparum with IC(50)s of 15 and 8.4 μM, respectively.

Rossinones A and B, Biologically Active Meroterpenoids from the Antarctic Ascidian, Aplidium species

Rossinones A (1) and B (2), biologically active meroterpene derivatives, were isolated from an Antarctic collection of the ascidian Aplidium species and structurally characterized with spectroscopic methods. The absolute configuration of 1 was deduced by using the modified Mosher method. The rossinones exhibit anti-inflammatory, antiviral and antiproliferative activities.

Synthesis and anti-inflammatory structure–activity relationships of thiazine–quinoline–quinones: Inhibitors of the neutrophil respiratory burst in a model of acute gouty arthritis

Sixteen new thiazine-quinoline-quinones have been synthesised, plus one bicyclic analogue. These compounds inhibited neutrophil superoxide production in vitro with IC(50)s as low 60 nM. Compounds with high in vitro anti-inflammatory activity were also tested in a mouse model of acute inflammation. The most active compounds inhibited both neutrophil infiltration and superoxide production at doses 2.5 micromol/kg, highlighting their potential for development as novel NSAIDs.

Anti-inflammatory and antimalarial meroterpenoids from the New Zealand ascidian Aplidium scabellum.

Bioassay-directed fractionation of an extract of the New Zealand ascidian Aplidium scabellum has afforded the anti-inflammatory secondary metabolite 2-geranyl-6-methoxy-1,4-hydroquinone-4-sulfate (1) and a family of pseudodimeric meroterpenoids scabellones A (2)-D (5). The benzo[c]chromene-7,10-dione scaffold contained within scabellones A-D is particularly rare among natural products. The structures were elucidated by interpretation of NMR data. Scabellone B was also identified as a moderately potent, nontoxic inhibitor of Plasmodium falciparum.

Enantiomeric Discorhabdin Alkaloids and Establishment of Their Absolute Configurations Using Theoretical Calculations of Electronic Circular Dichroism Spectra

Enantiomeric pairs of the cytotoxic pyrroloiminoquinone marine alkaloids discorhabdins B (2), G*/I (3), L (4), and W (5) have been isolated from Latrunculia species sponges collected at different locations around the coast of New Zealand. The absolute configuration of all compounds was secured by comparison of observed data with the results of time-dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) spectra. Enantiomeric discorhabdins exhibit equipotent antiproliferative biological activity.

In vitro culture and cryopreservation of Uronema marinum isolated from farmed New Zealand groper (Polyprion oxygeneios).

An in vitro culture method was developed for the ciliated protozoa Uronema marinum isolated from New Zealand aquacultured groper (Polyprion oxygeneios). Both formulated media and sterile seawater supplemented with homogenised fish tissue as a food source supported growth of U. marinum achieving cell densities of up to 1 x 10(5)cells/mL in culture. A cryopreservation method based on a cryomix formula of 20% glycerol, 10% fetal bovine serum and 70% cultured U. marinum, incorporating a slow freeze method to -80 degrees C, then liquid nitrogen storage, allowed cryogenic storage of cells and successful re-culture up to 12 months in storage.