Review: Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product

Marine natural products

This review covers the literature published in 2014 for marine natural products (MNPs), with 1116 citations (753 for the period January to December 2014) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1378 in 456 papers for 2014), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included

Potential anti-tumour compounds from marine sources

The search for potential anti-tumour compounds from marine sources has covered many areas of research. Initial investigations were made to ascertain any drug mode of action information contained in the readings of our in-house antiviral/cytotoxicity assays. These results, utilising clinical drugs with known modes of action, failed to indicate any obvious correlations. The extract of a New Zealand ascidian, Aplidium species D, was studied because extracts prepared from it always exhibited a wide range of biological activities. Bioassay directed fractionation led to the isolation of a novel metabolite cis-5-hydroxy-4-(4'-hydroxy-3'-methoxyphenyl)-4-(2"-imidazolyl)-1,2,3-trithiane, trithiane A. The structure was solved by extensive use of mass and NMR spectroscopy. The compound was found to be stable in acidified solutions, but under alkaline conditions was observed to interconvert to the 4-epi derivative, trithiane B and to decompose to 2-vanilloyl imidazole. Two competing base catalysed mechanisms were proposed to account for these observations. The relative stereochemistries of trithiane A and B were established by ¹H NMR NOE experiments, application of the modified Karplus equation and molecular mechanics modelling. Numerous attempts were made to crystallise trithiane A and to make crystalline derivatives. Only one reaction, oxidation to the monosulphoxide, gave any isolable products. The trithianes were found to be cytotoxic to both BSC monkey kidney cells and P388 leukemia cells and modestly inhibitory to bacteria and fungi. No efficacy against in vitro viruses was observed. A study based upon the chemical modification of discorhabdin C was carried out in order to produce compounds with more effective in vivo activity than discorhabdin C and to explore the structural features that could be responsible for the observed bioactivities of the discorhabdins. To this end, a new discorhabdin, E, was isolated and identified and six new derivatives were synthesised and characterised. Analysis of the biological activities of the discorhabdin derivatives suggested that structural features of ring E and possibly electron distribution changes in the iminoquinone moiety were responsible for the observed bioactivities

Synthesis and antimalarial evaluation of artesunate-polyamine and trioxolane-polyamine conjugates

A series of artesunate-polyamine and trioxolane-polyamine conjugates have been prepared. The conjugates were evaluated for antimalarial activity towards the K1 dual drug resistant and NF54 chloroquine-sensitive strains of Plasmodium falciparum (Pf) and for cytotoxicity towards the rat myoblast cell line L6. (Bis)-Boc-(bis)-artesunate-polyamine and (tetra)-artesunate-polyamine conjugates exhibited potent in vitro activity towards both strains of Pf, with IC50 values in the range of 0.3-1.1 nM, comparable to the parent artesunate. Cytotoxicity within this series of analogues typically increased with polyamine (PA) chain length, identifying the PA3-4-3 (spermine), and to some extent the PA3-7-3 series, as being highly selective towards the parasite. The corresponding series of (bis)-Boc-(bis)-trioxolane and (tetra)-trioxolane-polyamine conjugates were less active as antimalarials than the parent trioxolane acid, highlighting the limitation of using this warhead for drug-conjugate studies. Preliminary in vivo evaluation of two artesunate-polyamine conjugates 11 and 16 demonstrated 95.5-99.8% reduction in parasitaemia with maximal 30 day survival rates (ip delivery). Oral testing of 11 proved less efficacious, with 95.7% activity and inconsistent survival rates of 16-30 days. In contrast, trioxolane-polyamines were substantially less effective (ip delivery), exhibiting only modest reductions in parasitaemia and modest to no increase in survival rates

A Review of Fungal Protoilludane Sesquiterpenoid Natural Products

Natural products have been a great source for drug leads, due to a vast majority possessing unique chemical structures. Such an example is the protoilludane class of natural products which contain an annulated 5/6/4-ring system and are almost exclusively produced by fungi. They have been reported to possess a diverse range of bioactivities, including antimicrobial, antifungal and cytotoxic properties. In this review, we discuss the isolation, structure elucidation and any reported bioactivities of this compound class, including establishment of stereochemistry and any total syntheses of these natural products. A total of 180 protoilludane natural products, isolated in the last 70 years, from fungi, plant and marine sources are covered, highlighting their structural diversity and potential in drug discovery

Enantiomeric Variability of Distaminolyne A. Refinement of ECD and NMR Methods for Determining Optical Purity of 1-Amino-2-Alkanols

Sample configurations of distaminolyne A (1a); isolated from the ascidians Pseudodistoma opacum and P. cereum, and collected at different sites in New Zealand, were investigated by two methods: Exciton coupled electronic circular dichroism (EC ECD) of the corresponding N,O-dibenzoyl derivative 1b; and chiral reagent derivatization of 1a with (S)- and (R)-α-methoxyphenylacetic acid (MPA), followed by 1H-NMR analysis. Configuration and optical purity of 1a (%ee) was found to vary depending on the geographic distribution of ascidian colonies. An improved method for preparing N,O-diarenoyl derivatives of 1a was optimized. The EC ECD method was found to be complementary to the MPA-NMR method at different ranges of %ee

Bioinspired Syntheses of the Pyridoacridine Marine Alkaloids Demethyldeoxyamphimedine, Deoxyamphimedine, and Amphimedine

Efficient bioinspired syntheses of the biologically active pyridoacridine marine alkaloids demethyldeoxyamphimedine, deoxyamphimedine, and amphimedine are reported. Reaction of styelsamine D, prepared via an optimized route starting from Boc-dopamine, with paraformaldehyde afforded demethyldeoxyamphimedine and deoxyamphimedine. Oxidation of the latter using either K₃[Fe­(CN)₆] or DMSO/conc. HCl gave amphimedine in 8 steps from tryptamine with an overall yield of 14%. The versatility of the method was demonstrated by the synthesis of non-natural ethyl and benzyl congeners of deoxyamphimedine and amphimedine