Biomimetic total syntheses of linderaspirone A and bi-linderone and revisions of their biosynthetic pathways

Unlocking mild-condition benzene ring contraction using nonheme diiron N-oxygenase

Benzene ring contractions are useful yet rare reactions that offer a convenient synthetic route to various valuable chemicals. However, the traditional methods of benzene contraction rely on noble-metal catalysts under extreme conditions with poor efficiency and uncontrollable selectivity. Mild-condition contractions of the benzene ring are rarely reported. This study presents a one-step, one-pot benzene ring contraction reaction mediated by an engineered nonheme diiron N-oxygenase. Using various aniline substrates as amine sources, the enzyme causes the phloroglucinol-benzene-ring contraction to afford a series of 4-cyclopentene-1,3-dione structures. A reaction detail study reveals that the nonheme diiron N-oxygenase first oxidizes the aromatic amine to a nitroso intermediate, which then attacks the phloroglucinol anion and causes benzene ring contraction. Besides, we have identified two potent antitumor compounds from the ring-contracted products.

Palladium-Catalyzed Domino Reaction for the Assembly of Norbornane-Containing Chromones with Dimethyl Squarate as the Solid C1 Source

Reported herein is a novel palladium-catalyzed [2 + 2 + 1] domino annulation of 3-iodochromones, bridged olefins, and dimethyl squarate allowing the construction of chromone-containing polycyclic compounds in good to high yields. Importantly, dimethyl squarate is first employed as the solid C1 source in organic synthesis. Gram-scale experiments, late-stage modification of natural products, as well as transformations of products show potential for further synthetic elaborations.

Effects of Compounds Isolated from Lindera erythrocarpa on Anti-Inflammatory and Anti-Neuroinflammatory Action in BV2 Microglia and RAW264.7 Macrophage

Lindera erythrocarpa contains various constituents such as cyclopentenedione-, flavonoid-, and chalcone-type components. In this study, a novel bi-linderone derivative and 17 known compounds were isolated from the leaves of L. erythrocarpa by using various chromatographic methods. The structures of the components were determined from nuclear magnetic resonance and mass spectrometry data. All isolated compounds were tested for anti-inflammatory and anti-neuroinflammatory activities in lipopolysaccharide (LPS)-induced BV2 and RAW264.7 cells. Some of these compounds showed anti-inflammatory effects by inhibiting the nitric oxide (NO) produced by LPS. In particular, linderaspirone A (16), bi-linderone (17) and novel compound demethoxy-bi-linderone (18) showed significant inhibitory effects on the production of prostaglandin E2 (PGE₂), tumor necrosis factor-α, and interleukin-6. The three compounds also inhibited the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), which are pro-inflammatory proteins, and the activation of nuclear factor κB (NF-κB). Therefore, linderaspirone A (16), bi-linderone (17), and demethoxy-bi-linderone (18) isolated from the leaves of L. erythrocarpa have therapeutic potential in neuroinflammatory diseases.

Small rings in the bigger picture: ring expansion of three- and four-membered rings to access larger all-carbon cyclic systems

The release of the inherent ring strain of cyclobutane and cyclopropane derivatives allows a rapid build-up of molecular complexity. This review highlights the state-of-the-art of the ring expansions of three- and four-membered cycles and is organised by types of reactions with emphasis on the reaction mechanisms. Selected examples are discussed to illustrate the synthetic potential of this elegant synthetic tool.

Photoinitiated Cascade for Rapid Access to Pyrroloquinazolinone Core of Vasicinone, Luotonins, and Related Alkaloids

Furylimines of aromatic o-nitro aldehydes undergo a photoinduced cascade transformation offering rapid atom- and step-economical access to complex polyheterocyclic scaffolds possessing a privileged pyrroloquinazolinone core.

Lindera cyclopentenedione intermediates from the roots of Lindera aggregata

Chromatographic fractionation of the roots of Lindera aggregata has led to the isolation of three new monomers of Lindera cyclopentenedione derivatives (1–3), a pair of new enantiomers of bi-linderone derivatives (4a/4b), and six known Lindera cyclopentenediones (5–8 and 9a/9b). Their structures were determined by NMR and MS data. The absolute configurations of the new bi-linderone derivative enantiomers (4a/4b) were determined by ECD calculation. (±)-Lindepentone A (1) presents the novel skeleton of 3,5-dioxocyclopent-1-enecarboxylate. Lindoxepines A (2) and B (3) present an unprecedented oxepine-2,5-dione derivative skeleton, which may be enlightening for the in vivo biosynthesis of the monomers of Lindera cyclopentenediones. A possible biosynthetic pathway for 1 and a plausible biosynthetic pathway from stilbenes to Lindera cyclopentenediones via the key intermediates 2 and 3 were postulated. The inhibitory activity of these compounds against three microorganisms was also evaluated.

Lindera cyclopentenediones together with their dimers and novel biosynthetic intermediates were isolated from Lindera aggregata.

New anti-angiogenic leading structure discovered in the fruit of Cimicifuga yunnanensis

Cimyunnins A–C (1–3), characterized with an unusual fused cyclopentenone ring G, together with cimyunnin D (4), possessing a highly rearranged γ-lactone ring F, were characterized from the fruit of Cimicifuga yunnanensis. Their structures were elucidated by spectroscopic analysis, X-ray diffraction, and density functional theory calculations. In addition, cimyunnin A exhibited comparable anti-angiogenic activities to those of sunitinib, a clinically-used first-line angiogenesis inhibitor, in the in vitro and ex vivo studies.

Total syntheses of natural products containing spirocarbocycles

The spiro motif is becoming an increasingly prevalent structure in medicinal and organic chemistry. The total syntheses of natural products containing all-carbon spirocycles is reviewed.

Cyclopent-4-ene-1,3-diones: a new class of herbicides acting as potent photosynthesis inhibitors

In a recent paper, we reported the synthesis and photosynthesis-inhibitory activity of a series of analogues of rubrolides. From quantitative structure-activity relationship (QSAR) studies, we found that the most efficient compounds are those having higher ability to accept electrons. On the basis of those findings, we directed our effort to synthesize new analogues bearing a strong electron-withdrawing group (nitro) in the benzylidene ring and evaluate their effects on photosynthesis. However, the employed synthetic approach led to novel cyclopent-4-ene-1,3-diones as major products. Here, we report the synthesis and mechanism of action of such cyclopent-4-ene-1,3-diones as a new class of photosynthesis inhibitors. These compounds block the electron transport at the QB level by interacting at the D1 protein at the reducing side of Photosystem II and act as Hill reaction inhibitors, with higher activity than the corresponding rubrolides. To the best of our knowledge, this is the first report on the photosynthesis inhibitory activity of cyclopentenediones.