Exploration of a proposed biomimetic synthetic route to plumarellide. Development of a facile transannular Diels–Alder reaction from a macrocyclic enedione leading to a new 5,6,7-tricyclic ring system

Hypoxia-Protective Azaphilone Adducts from Peyronellaea glomerata

Peyronellones A and B (1 and 2), a pair of rare tetracyclic caged adducts of azaphilone with pyruvic acid, along with four new analogues (3-6), were isolated from solid cultures of the endophytic fungus Peyronellaea glomerata. Their structures were elucidated through spectroscopic analysis, and their absolute configurations were unambiguously determined by a combination of single-crystal X-ray crystallography, Rh₂(OCOCF₃)₄-induced ECD experiments, ECD calculations, and modified Mosher methods. Compound 2 (5 μM) was found to have a significant hypoxia-protective effect that improved the survival rate of hypoxia/reoxygenation-treated human umbilical vein endothelial cells from 35% to 70%, which was equal to the potency of the positive control, verapamil. Flow cytometry analysis suggested 2 could inhibit H/R-induced late-stage apoptosis of this cell line.

Polycyclic Furanobutenolide-Derived Cembranoid and Norcembranoid Natural Products: Biosynthetic Connections and Synthetic Efforts

The polycyclic furanobutenolide-derived cembranoid and norcembranoid natural products are a family of congested, stereochemically complex, and extensively oxygenated polycyclic diterpenes and norditerpenes. Although the elegant architectures and biological activity profiles of these natural products have captured the attention of chemists since the isolation of the first members of the family in the 1990s, the de novo synthesis of only a single polycyclic furanobutenolide-derived cembranoid and norcembranoid has been accomplished. This article begins with a brief discussion of the proposed biosyntheses and biosynthetic connections among the polycyclic furanobutenolide-derived cembranoids and norcembranoids and then provides a comprehensive review of the synthetic efforts toward each member of the natural product family, including biomimetic, semisynthetic, and de novo synthetic strategies. This body of knowledge has been gathered to provide insight into the reactivity and constraints of these compact and highly oxygenated polycyclic structures, as well as to offer guidance for future synthetic endeavors.

Copper(I)/Ligand-Catalyzed 5-endo Radical Cyclization-Aromatization of 2,2,2-Trichloroethyl Vinyl Ethers: Synthesis of 2,3-Difunctionalized 4-Chlorofurans

Copper(I)/ligand-catalyzed one pot synthesis of highly substituted 2,3-difunctionalized-4-chlorofurans has been reported. The reaction proceeds via a Cu(I)-catalyzed regioselective 5-endo-trig radical cyclization of 2,2,2-trichloroethyl vinyl ethers followed by the base-promoted dehydrochlorination. The success of the kinetically disfavored 5-endo cyclization was attributed to the formation of captodatively stabilized radical intermediate in the cyclization step and relatively high reaction temperature. Synthetic application of this protocol was also demonstrated in the preparation of alkyl and aryl substituted 4-chlorofuranonapthoquinones.

Investigation of transannular cycloaddition reactions involving furanoxonium ions using DFT calculations. Implications for the origin of plumarellide and rameswaralide and related polycyclic metabolites isolated from corals

DFT calculations probing potential cycloaddition pathways leading to the polycyclic ring systems found in the coral secondary metabolites plumarellide, mandapamate and rameswaralide are described.

Synthesis of a highly functionalized core of verrillin

An efficient stereoselective synthesis of furanoverrillin (5), a highly functionalized core of verrillin (1), is reported. The synthetic strategy is based on constructing bicyclic lactone 17 prior to the 10-membered ring macrocyclization. The effect of the C4 methyl group on the furan reactivity is also discussed.

Increasing the efficiency of the transannular Diels-Alder strategy via palladium(II)-catalyzed macrocyclizations

Palladium(II)-catalyzed macrocyclizations of bis(vinylboronate ester) compounds are demonstrated to provide a strategically efficient approach to transannular Diels-Alder reaction substrates. In several systems reported, the macrocycle is preorganized such that cycloaddition at room temperature occurs concomitantly with cyclization. Numerous advantages over palladium(0)-catalyzed cross-coupling approaches are demonstrated.