Dinoflagellate-Related Amphidinolides from the Brazilian Octocoral Stragulum bicolor

Advances Toward Amphidinolides C, F and U: Isolations, Synthetic Studies and Total Syntheses

Amphidinolides C, F, and U, including C2-C4 analogs, are highly cytotoxic marine macrolides, mainly isolated from dinoflagellates of the genus Amphidinium. All these polyketides share a 75 % or more similar structure, highlighted by a macrolactone ring, at least one trans-2,5-substituted-THF motif and a characteristic polyenic side chain. From their isolation and absolute configurational assignment, the total synthesis of these marine macrolides represented an intense challenge to the organic synthesis community over the last 15 years, with around 14 research groups engaged in this inspiring task. In the first part of this review, we present the different approaches to the isolation and characterization of these natural products, including the most recent analogs, which may cast doubt on the biogenetic origin of these compounds. The various synthetic approaches to the total synthesis of C, F, and U amphidinolides are presented in a second part, focusing on key reactions and/or innovative strategies. The review concludes in a third section summarizing the successful approaches leading to the total synthesis of one of the members of this amphidinolide subfamily.

Potent Cytotoxic Analogs of Amphidinolides from the Atlantic Octocoral Stragulum bicolor

Amphidinolides are cytotoxic macrolides produced by symbiotic unicellular microalgae of the genus Amphidinium. Here we describe the identification of four related molecules belonging to this macrolide family isolated from the invertebrate Stragulum bicolor. The new molecules, named amphidinolide PX1-PX3 and stragulin A (1–4), show an unprecedented carbon skeleton whose complete stereochemistry has been determined by spectroscopic and computational methods. Differences in the structures of these molecules modulate their biological activity in a panel of tumor cell lines, but the opened derivative stragulin (4) shows a very potent and specific cytotoxic activity (IC₅₀ 0.18 µM) against the aggressive human melanoma cell A2058.

The Marine Dinoflagellate Alexandrium andersoni Induces Cell Death in Lung and Colorectal Tumor Cell Lines

Dinoflagellates are one of the most important components in marine phytoplankton, second only to diatoms as primary producers. Dinoflagellates have also been reported to produce bioactive secondary metabolites such as polyethers and macrolides with potential applications as pharmaceuticals. Here, we tested the effect of the organic extract and its related enriched extracts from solid-phase extraction (SPE) of a strain of the dinoflagellate Alexandrium andersoni. We found that the SPE extracts induced high cytotoxicity towards two cancer cell lines (A549 lung cancer and HT29 colorectal cancer) without affecting normal cell viability. The SPE extracts activated two different cell death pathways in the two tumor cell lines at the gene expression level, with the involvement of the major mediators of the tumor necrosis factor (TNF) cell signaling cascade. In HT29 cells, in addition to TNF activation, a death signaling pathway in response to DNA damage was also induced. This is an interesting finding since the HT29 cell line is highly aggressive since it is p53 gene-defect and this DNA instability renders this type of cancer very resistant towards all chemotherapeutic agents. Another significant result is that two distinct chemical fractions were selectively able to induce different and specific responses on the two different tumor cells treated.

Marine natural products

Covering: 2016. Previous review: Nat. Prod. Rep., 2017, 34, 235-294This review covers the literature published in 2016 for marine natural products (MNPs), with 757 citations (643 for the period January to December 2016) 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 (1277 in 432 papers for 2016), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included.

Stereoselective Synthesis of the C1-C9 and C11-C25 Fragments of Amphidinolides C, C2, C3, and F

An efficient synthesis of the C1-C9 and the C11-C25 fragments of amphidinolides C, C2, C3, and F from a common intermediate is reported. The construction of the C1-C9 fragment involves an intramolecular hetero-Michael cyclization to form the 3,5-disubstituted trans-tetrahydrofuran moiety. The approach to prepare the C11-C25 fragment utilizes a highly stereoselective aerobic cobalt-catalyzed alkenol cyclization and a chelated Mukaiyama aldol reaction to form the C13-C14 bond and to concomitantly install the C13 hydroxyl group.