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Fraxinellone (1) is a naturally occurring degraded limonoid isolated from Meliaceae and Rutaceae plants. As a potential natural-product-based insecticidal agent, fraxinellone has been structurally modified to improve its activity. Furan ring of fraxinellone is critical in exhibiting its insecticidal activity, but with few modifications. Herein, C-ring-modified cyclopropyl analogues were semi-synthesized by Rh(II)-catalyzed cyclopropanation. The structures of the target compounds were well characterized by NMR and HRMS. The precise three-dimensional structural information of 3a was established by X-ray crystallography. Their insecticidal activity was evaluated against Mythimna separata Walker by a leaf-dipping method. Compound 3c exhibited stronger insecticidal activity than 1 and toosendanin against M. separata with teratogenic symptoms during the different periods, implying that cyclopropanation of the furan ring could strengthen the insecticidal activity of fraxinellone.

No abstract

Natural systems produce various γ-dicarbonyl-bearing compounds that can covalently modify lysine in protein targets via the classic Paal-Knorr reaction. Among them is a unique class of lipid-derived electrophiles - isoketals...