Total Synthesis of seco-Plakortolide E and (−)-ent-Plakortolide I: Absolute Configurational Revision of Natural Plakortolide I

Synthesis of Plakortolides E and I Enabled by Base Metal Catalysis

A protecting-group-free synthesis of two endoperoxide natural products, plakortolide E and plakortolide I, is reported. Key steps are a vanadium-mediated epoxidation, an iron-catalyzed allylic substitution, and a cobalt-induced endoperoxide formation. Our approach combines chemoselective bond-forming reactions and one-pot operations to forge an overall efficient synthesis.

Enantioselective Synthesis Muqubilin and Negombatoperoxides B and C/D

Muqubilin, negombatoperoxide B, and negombatoperoxide C/D were synthesized through enantioselective routes, with the quaternary center derived from a peroxy chiral building block of known absolute configuration. The C-2/C-3 stereogenic centers were introduced by asymmetric aldol condensation, and the 1,2-dioxane ring was constructed via an intramolecular alkylation of a hydroperoxide with a mesylate. The synthetic samples showed physical and spectroscopic data consistent with those reported in the literature and thus verified the configurations of the natural products. A potentially more expeditious enantioselective entry to the 1,2-dioxane-aldol moiety (C-1 to C-6) of such cyclic peroxides was also briefly explored, where the C-2/C-3 stereogenic centers were installed through a [2+2] cycloaddition and the 1,2-dioxane ring was closed via an intramolecular alkylation coupled with an alkyl-oxygen cleavage of a β-lactone.

Peroxides with Anthelmintic, Antiprotozoal, Fungicidal and Antiviral Bioactivity: Properties, Synthesis and Reactions

The biological activity of organic peroxides is usually associated with the antimalarial properties of artemisinin and its derivatives. However, the analysis of published data indicates that organic peroxides exhibit a variety of biological activity, which is still being given insufficient attention. In the present review, we deal with natural, semi-synthetic and synthetic peroxides exhibiting anthelmintic, antiprotozoal, fungicidal, antiviral and other activities that have not been described in detail earlier. The review is mainly concerned with the development of methods for the synthesis of biologically active natural peroxides, as well as its isolation from natural sources and the modification of natural peroxides. In addition, much attention is paid to the substantially cheaper biologically active synthetic peroxides. The present review summarizes 217 publications mainly from 2000 onwards.

Advances in the synthesis of acyclic peroxides

This review summarises the many developments in the synthesis of acyclic peroxides, with a particular focus on the past 20 years, and seeks to update organic chemists about these new approaches.

Mn-, Fe-, and Co-Catalyzed Radical Hydrofunctionalizations of Olefins

Cofactor-mimetic aerobic oxidation has conceptually merged with catalysis of syngas reactions to form a wide range of Markovnikov-selective olefin radical hydrofunctionalizations. We cover the development of the field and review contributions to reaction invention, mechanism, and application to complex molecule synthesis. We also provide a mechanistic framework for understanding this compendium of radical reactions.

Structural diversity and chemical synthesis of peroxide and peroxide-derived polyketide metabolites from marine sponges

The structural elucidation, chemical synthesis and therapeutic potential of peroxide and peroxide-derived sponge metabolites, with special focus on their intriguing structural similarities and differences from a biogenetic perspective, are reviewed.

Synthesis and Structural Reassignment of Plakinidone

In connection with its first synthesis, plakinidone was structurally revised to a five-membered lactone. The key evidence for the previous assignment of this natural product as a perlactone was proven to be a misinterpretation of the MS data because of unawareness of a facile air oxidation. The synthetic samples also allowed for detection of differences in (13)C NMR for diastereomers of remote stereogenic centers, along with the influence of the air oxidation on the optical rotation.

Expeditious entry to the chamigrane endoperoxide family of natural products

Several members of the recently reported peroxy chamigrane family of natural products were synthesized via a distereoselective route with a novel facial-selective epoxidation of a spiroundecadiene, a facile epoxide rearrangement, and a Co(II)-mediated silylperoxidation as the key steps. Adaptation of the diastereoselective route to an enantioselective one is also illustrated.

Construction of the tricyclic core of steenkrotin-type diterpenoids via intramolecular [3 + 2] cycloaddition

A concise and diastereoselective route to the [5–6–7] tricyclic skeleton of steenkrotins was developed based on an intramolecular [3 + 2] cycloaddition.

Synthesis of silyl monoperoxyketals by regioselective cobalt-catalyzed peroxidation of silyl enol ethers: application to the synthesis of 1,2-dioxolanes

The cobalt-catalyzed peroxidation of silyl enol ethers with molecular oxygen and triethylsilane provided silyl monoperoxyketals in 54%-96% yield. These compounds serve as precursors to peroxycarbenium ions, which undergo annulations to provide 1,2-dioxolanes.

Marine natural products

This review covers the literature published in 2012 for marine natural products, with 1035 citations (673 for the period January to December 2012) 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 (1241 for 2012), together with the relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Peroxy natural products

This review covers the structures and biological activities of peroxy natural products from a wide variety of terrestrial fungi, higher plants, and marine organisms. Syntheses that confirm or revise structures or stereochemistries have also been included, and 406 references are cited.

Plakortolide stereochemistry revisited: the checkered history of plakortolides e and I

The relative configuration of the plakortolide metabolite (4) isolated from a Madagascan Plakortis sp. and named (+)-plakortolide I is revised following reassignment of the ¹³C signals for C-7 and C-16, thereby establishing that the metabolite isolated was likely (+)-plakortolide E (3). We propose that the name "plakortolide I" should be retained for the plakortolide metabolite 5 first isolated by the Faulkner group; its enantiomer 4 can then be named ent-plakortolide I in line with the description of Barnych and Vatèle. The spectroscopic data for MPA esters prepared from synthetic samples of seco derivatives of plakortolide E (3) and ent-plakortolide I (4) were compared with those of MPA esters of seco derivatives from naturally isolated plakortolides L (1) and K (2) and of seco-plakortolide E (6a). Likewise, the spectroscopic data for MTPA esters derived from 3 and 4 were compared with data for the MTPA esters derived from 5. These various comparisons established that the sign of the specific rotation associated with the natural isolates is an unreliable indicator of absolute configuration and verify that the absolute configurations of plakortolides L (1), K (2), E (3), and I (5) are (3S, 4S, 6S), (3R, 4R, 6S), (3R, 4R, 6R), and (3S, 4S, 6R), respectively.