Furan-Site Bromination and Transformations of Fraxinellone as Insecticidal Agents Against Mythimna separata Walker

Abstract

Furan ring of limoninoids is critical in exhibiting insecticidal activity. Herein, fraxinellone (1) was used as a template of furan-containing natural products and a series of its derivatives was synthesized by selective bromination in good yields on gram-scale and following Suzuki-Miyaura or Sonogashira coupling reactions in moderate to good yields. Bromination of limonin (9) was also accomplished without altering other functional groups in high yield. Furthermore, an evaluation of insecticidal activity against the instar larvae of Mythimna separata showed that derivatives 2, 3b, 3g, 5a, 5d and 5h displayed more potent insecticidal activity than 1 and toosendanin.

Furan-site transformations of obacunone as potent insecticidal agents

“…However, treatment with 0.5 eq DBDMH gave the mixture of at least three components containing monobromination 2 (21%), dibromination 3 (<5%) and recovered 1 (21%). When NBS or NBS with catalytic Br 2 was carried out this reaction, no product was obtained (data not shown), which was different from previous studies on fraxinellone [36], indicating that DBDMH is more suitable for the furan-site bromination of obacunone. Consequently, 3 was prepared in gram-scale with 1.4 eq DBDMH in 58% yield in Fig.…”

“…The insecticidal activity of 1-3 and 3a-j was tested as the mortality rate values by using the leaf-dipping method against the pre-third-instar larvae of Mythimna separate using the reported procedure [36]. For each sample, a total of 24 pre-third-instar larvae (6 larvae per group) were used.…”

“…Recently, we reported the bromination of fraxinellone by N -bromosuccinimide (NBS, as a brominating reagent) and Br 2 (as a catalyst) or by 1,3-dibromo-5,5-dimethylhy-dantoin (DBDMH, another brominating reagent) and following couplings, and found some furan-site modified derivatives displayed more potent insecticidal activity than toosendanin [36]. In our endeavor aiming at finding more active natural product-based insecticidal hits [36, 37, 38, 39, 40], herein we prepared a series of furan-site transformed derivatives of obacunone ( 1 ) by selectively altering furan ring (Fig. 2).…”

Semi-Synthesis of C-Ring Cyclopropyl Analogues of Fraxinellone and Their Insecticidal Activity Against Mythimna separata Walker

“…However, the furan ring of fraxinellone remains with few modifications. Recently, the modification of aromatic (furan ring) functionalities was reported by us [19,20]. A series of C-ring selective brominations and further palladium-catalyzed transformations analogues of fraxinellone have been prepared.…”

“…To our delight, some compounds displayed more potent insecticidal activity than toosendanin. On the basis of the above furan-modified results and in our endeavor aiming at finding more active natural-product-based insecticidal hits [19,[21][22][23][24], herein, we semi-synthesized C-ring cyclopropyl analogues of fraxinellone by Rh(II)-catalyzed cyclopropanation as insecticidal agents against M. separata.…”