Covering: 1972 to 2011 This review covers the literature of prenylated quinone, hydroquinone and naphthoquinone marine natural products with reported cytotoxic and/or antioxidant properties. The structures, biological activity and, where applicable, the syntheses of 159 cytotoxic/antioxidant compounds, isolated from various marine organisms, are presented, while trends in the distribution of these cytotoxic metabolites, across the different marine phyla, are highlighted. Marine prenylated quinones, hydroquinones and naphthoquinones are of mixed polyketide and terpenoid biogenesis and recent biosynthetic studies of selected compounds are discussed.

The marine red algae of the genus Laurencia have been widely studied for their structurally diverse and biologically active secondary metabolites. We report here the natural product investigation of the organic extract of a newly identified South African endemic species, Laurencia alfredensis. A sequence of column chromatography, preparative TLC and normal phase HPLC resulted in the isolation of eleven compounds comprising three labdane-type diterpenes (1–3), four polyether triterpenes (4–7), three cholestane-type ecdysteroids (8–1 0) and a glycolipid (11). Compounds 1–3, 5–8 and 10 have not previously been reported, while compound 9 is reported here for the first time from a natural source and the known compound 11 isolated for the first time from the genus Laurencia. The structural elucidation and the relative configuration assignments of the compounds were accomplished by extensive use of 1D- and 2D-NMR, HR-ESI-MS, UV and IR spectroscopic techniques, while the absolute configuration of compound 1 was determined by single-crystal X-ray diffraction analysis. All compounds were evaluated against the MDA-MB-231 breast and HeLa cervical cancer cell lines. Compound 2 exhibited low micromolar antiproliferative activity (IC₅₀ = 9.3 µM) against the triple negative breast carcinoma and compound 7 was similarly active (IC₅₀ = 8.8 µM) against the cervical cancer cell line.

Bioinformatic analysis of data from the NCI-60 cell cytotoxicity screen revealed a subset of extracts that showed selective cytotoxic activity toward human colon carcinoma cell lines. Bioassay-guided fractionation of a colon cancer selective extract from a Philippines collection of the marine sponge Corticium niger provided two new steroidal alkaloids, plakinamines N (1) and O (2), along with two known compounds of the plakinamine class (3, 4). The structures of these compounds were elucidated by interpretation of combined MS and NMR spectroscopic data. Plakinamines N (1), O (2), and J (4) were tested for antiproliferative activity in the NCI-60 screen, and they showed enhanced inhibitory effects against all of the colon cell lines with mean GI₅₀ values of 11.5, 2.4, and 1.4 μM, respectively.

In this paper, we report on the chemistry of the rare South African Actinomycete Kribbella speibonae strain SK5, a prolific producer of hydroxamate siderophores and their congeners. Two new analogues, dehydroxylated desferrioxamines, speibonoxamine 1 and desoxy-desferrioxamine D₁ 2, have been isolated, together with four known hydroxamates, desferrioxamine D₁ 3, desferrioxamine B 4, desoxy-nocardamine 5 and nocardamine 6, and a diketopiperazine (DKP) 7. The structures of 1–7 were characterized by the analysis of HRESIMS and 1D and 2D NMR data, as well as by comparison with the relevant literature. Three new dehydroxy desferrioxamine derivatives 8–10 were tentatively identified in the molecular network of K. speibonae strain SK5 extracts, and structures were proposed based on their MS/MS fragmentation patterns. A plausible spb biosynthetic pathway was proposed. To the best of our knowledge, this is the first report of the isolation of desferrioxamines from the actinobacterial genus Kribbella.