A Rapid Entry to Diverse γ-Ylidenetetronate Derivatives through Regioselective ­Bromination of Tetronic Acid Derived γ-Lactones and Metal-Catalyzed Postfunctionalization

Collective synthesis of aspulvinone and its analogues by vinylogous aldol condensation of substituted tetronic acids with aldehydes

A mild, modular and efficient synthetic method with broad substrate scope was developed for aspulvinones. Nine natural aspulvinones were synthesized, six of which were for the first time. The aldol condensation delivered Z-configuration products predominantly in MeCN. Meanwhile, alkoxy exchange occurred in MeOH and EtOH. Aspulvinone O and E, and substrate 49, 50, and 51 exhibited modest anti-SARS-CoV-2 activity in a high-throughput screening and enzyme kinetics assay.

Evaluation of ferrocenyl-containing γ-hydroxy-γ-lactam-derived tetramates as potential antiplasmodials

A series of ferrocenyl-containing γ-hydroxy-γ-lactam tetramates were prepared in 2-3 steps through ring opening-ring closure (RORC) process of γ-ylidene-tetronate derivatives in the presence of ferrocenyl alkylamines. The compounds were screened in vitro for their antiplasmodial activity against chloroquine-sensitive (3D7) and chloroquine-resistant (W2) clones of P. falciparum, displaying activity in the range of 0.12-100 μM, with generally good resistance index. The most active ferrocene in these series exhibited IC₅₀ equal to 0.09 μM (3D7) and 0.12 μM (W2). The low cytotoxicity of the ferrocenyl-containing γ-hydroxy-γ-lactam tetramates against Human Umbilical Vein Endothelial (HUVEC) cell line demonstrated selective antiparasitic activity. The redox properties of these ferrocene-derived tetramates were studied and physico-biochemical studies evidenced that these derivatives can exert potent antimalarial activities via a mechanism distinct from ferroquine.

Recent advances in the synthesis of naturally occurring tetronic acids

During the last decades the interest towards natural products containing the tetronic acid moiety augmented significantly, due to their challenging structures and to the wide range of biological activities they display. This increasing enthusiasm has led to noteworthy advances in the development of innovative methodologies for the construction of the butenolide nucleus. This review provides an overview of the progress in the synthesis of tetronic acid as a structural key motif of natural compounds, covering the last 15 years. Herein, the most representative synthetic pathways towards structurally diverse natural tetronic acids are grouped according to the strategy followed. The first part describes the functionalization of a preformed tetronic acid core by intermolecular reactions (cross-coupling reactions, nucleophilic substitution, multicomponent reactions) whereas the second part deals with intramolecular approaches (Dieckmann, cycloaddition or ring expansion reactions) to construct the heterocyclic core. This rational subcategorization allowed us to make some considerations about the best approaches for the synthesis of specific substrates, including modern intriguing methodologies such as microwave irradiation, solid phase anchoring, bio-transformations and continuous flow processes.

Enantioselective total syntheses of (+)-stemofoline and three congeners based on a biogenetic hypothesis

The powerful insecticidal and multi-drug-resistance-reversing activities displayed by the stemofoline group of alkaloids render them promising lead structures for further development as commercial agents in agriculture and medicine. However, concise, enantioselective total syntheses of stemofoline alkaloids remain a formidable challenge due to their structural complexity. We disclose herein the enantioselective total syntheses of four stemofoline alkaloids, including (+)-stemofoline, (+)-isostemofoline, (+)-stemoburkilline, and (+)-(11S,12R)-dihydrostemofoline, in just 19 steps. Our strategy relies on a biogenetic hypothesis, which postulates that stemoburkilline and dihydrostemofolines are biogenetic precursors of stemofoline and isostemofoline. Other highlights of our approach are the use of Horner–Wadsworth–Emmons reaction to connect the two segments of the molecule, an improved protocol allowing gram-scale access to the tetracyclic cage-type core, and a Cu-catalyzed direct and versatile nucleophilic alkylation reaction on an anti-Bredt iminium ion. The synthetic techniques that we developed could also be extended to the preparation of other Stemona alkaloids.

Stemofoline alkaloids are promising lead structures for further development in the fields of agriculture and medicine. Here, the authors report the enantioselective total syntheses of four stemofoline alkaloids in 19 steps based on a biogenetic hypothesis.

Synthesis and biological evaluation of pyridazinone derivatives as potential anti-inflammatory agents

Cyclic nucleotide phosphodiesterase type 4 (PDE4), that controls intracellular level of cyclic nucleotide cAMP, has aroused scientific attention as a suitable target for anti-inflammatory therapy in respiratory diseases. Here we describe the development of two families of pyridazinone derivatives as potential PDE4 inhibitors and their evaluation as anti-inflammatory agents. Among these derivatives, 4,5-dihydropyridazinone representatives possess promising activity, selectivity towards PDE4 isoenzymes and are able to reduce IL-8 production by human primary polymorphonuclear cells.