Covering: up to the end of 2013 Cu-mediated C(sp²)–N bond formation has received intense interest recently, and has been applied to the total synthesis of a wide variety of structurally complex natural products. This review covers the synthetic assembly of peptide natural products in which Cu-mediated enamide formation is the key transformation. The total syntheses of cyclopeptide alkaloids, pacidamycin D, and yaku'amide A exemplify the versatility of the Cu-catalyzed cross-coupling reaction in comparison to other synthetic methods.

Direct substitution of hydrogen in C(sp³)–H bonds by 4-pyridine was achieved by employing benzophenone and 4-cyanopyridine in aqueous acetonitrile under photo-irradiating conditions. This simple and mild 4-pyridination proceeds in a highly chemoselective manner especially at benzylic C(sp³)–H bonds without affecting polar functional groups, and enables intermolecular formation of sterically hindered bonds between alkylaromatics and 4-pyridine. The present methodology thus serves as a powerful tool for construction of biologically active and functional molecules with 4-pyridine substructures.

The direct alkenylation of C(sp³)–H bonds was achieved by employing benzophenone and 1,2-bis(phenylsulfonyl)ethylene under photo-irradiation conditions. This simple metal-free reaction enables the substitution of heteroatom-substituted methine, methylene and aliphatic C(sp³)–H bonds by (E)-sulfonylalkene units in a highly chemoselective manner. The derived sulfonylalkenes were further converted in a single step to the prenyl derivatives via a second photo-induced radical substitution and to the pyrrole derivatives via cyclization and aromatization steps. The present protocol thus serves as an efficient method for the direct extension of carbon skeletons for the synthesis of structurally complex natural products and pharmaceuticals.

Recent studies on the respiratory chain of Ascaris suum showed that the mitochondrial NADH-fumarate reductase system composed of complex I, rhodoquinone and complex II plays an important role in the anaerobic energy metabolism of adult A. suum. The system is the major pathway of energy metabolism for adaptation to a hypoxic environment not only in parasitic organisms, but also in some types of human cancer cells. Thus, enzymes of the pathway are potential targets for chemotherapy. We found that flutolanil is an excellent inhibitor for A. suum complex II (IC₅₀ = 0.058 μM) but less effectively inhibits homologous porcine complex II (IC₅₀ = 45.9 μM). In order to account for the specificity of flutolanil to A. suum complex II from the standpoint of structural biology, we determined the crystal structures of A. suum and porcine complex IIs binding flutolanil and its derivative compounds. The structures clearly demonstrated key interactions responsible for its high specificity to A. suum complex II and enabled us to find analogue compounds, which surpass flutolanil in both potency and specificity to A. suum complex II. Structures of complex IIs binding these compounds will be helpful to accelerate structure-based drug design targeted for complex IIs.