New Insecticidal Agents from Halogenation/Acylation of the Furyl-Ring of Fraxinellone

Abstract

Introduction of the halogen atom or the acyl group at the C-ring of fraxinellone was investigated. Some unexpected halogenation products were obtained with the different chlorination/bromination reagents, and their possible reaction mechanisms were also proposed. Seven key steric structures of 2a’, 2b, 2b’, 2c’, 3a, 3b, and one isomer (5’α-Cl) of 2a were further confirmed by single-crystal X-ray diffraction. Especially compounds 2a, 2a’, 3a and 3c exhibited more potent insecticidal activity than toosendanin. Some structure-activity relationships of tested compounds were also described.

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

“…The furan ring of fraxinellone ( 1 ) was previously brominated at the C-2′ and C-5′ positions using NBS (Fig. 2 ) 34 ; however, these reaction conditions produced either low or highly variable yields. In order to optimize the reaction conditions to obtain the monobromofraxinellone or dibromofraxinellone selectively in a higher yield, a reduced fraxinellone ( 2 ) was used as the starting material for excluding the possible effect of C-2 and C-3 double bonds in the NBS bromination reaction of 1 .…”

“…Interestingly, they also reported that fraxinellone-based esters and hydrazones derivatives at C-4/C-10 position (A-ring) displayed higher insecticidal activity 31 – 33 . In contrast, the lack of chemical handle on the furan ring has limited the derivatives with the furan ring intact to only a few examples 34 . Since the importance has implicated the furan ring, such derivatives would be useful in elucidating additional SAR.…”

“…The modification of aromatic functionalities of NPs could be accomplished by introducing a halide using enzymatic 17 , 18 , 35 or chemical methods 36 , followed by further diversification using various palladium-catalyzed transformations 20 . The furan ring of 1 was previously halogenated selectively at the C-2′ and C-5′ position using N -bromosuccinimide (NBS) or N -chloromosuccinimide (NCS), however, the reaction conditions only gave dihalofraxinellone 6 and lactone 7 in very low yields 34 (less than 30% in total) (Fig. 2 ).…”

Application of Sustainable Natural Bioesources in Crop Protection: Insight into a Podophyllotoxin-Derived Botanical Pesticide for Regulating Insect Vestigial Wing of Mythimna separata Walker

“…In continuation of our program to discover new natural-product-based insecticidal agents, by using podophyllotoxin ( 1 , Figure a), a sustainable naturally occurring cyclolignan isolated from Juniperus Sabina (widely distributed in northwestern China), as a lead compound, we prepared a series of 4α-acyloxy-2′(2′,6′)-(di)­halogenopodophyllotoxin derivatives ( 2 , Figure a) . They mainly showed the potent growth inhibitory activity against third-instar larvae of M. separata as we reported other natural-product-based insecticidal agents such as obacunone and fraxinellone. , When compared with that of the blank control (33 days), the growth duration from the third-instar larva to moth was shortened to 30 days in the treated groups. Interestingly, many malformed moths with imperfect wings in the treated groups appeared during the stage of adult emergence (Figure b) .…”

Furan-site transformations of obacunone as potent insecticidal agents

“…1). Yet, the lack of furan-site chemical handle has limited the furan-site diversity of NPs [19]. Obacunone ( 1 , Fig.…”