Synthesis and insecticidal activity of novel dihydropyrrole derivatives with N-sulfanyl,sulfinyl, and sulfonyl moieties

This paper reports the synthesis and insecticidal activity of a new type of dihydropyrrole derivatives with sulfur moieties such as sulfanyl, sulfinyl, and sulfonyl groups at the 1-position. These derivatives exhibited high insecticidal potency against Nilaparvata lugens and Nephotettix cincticeps. Investigation of the structure-activity relationships revealed that the alkoxycarbonyloxy groups at the 4-position tended to increase the systemic insecticidal activity.     

Unprecedented oxidation of a biologically active aroylhydrazone chelator catalysed by iron(III): serendipitous identification of diacylhydrazine ligands with high iron chelation efficacy

Ligands of the 2-pyridylcarbaldehyde isonicotinoylhydrazone class show high iron (Fe) sequestering efficacy and have potential as agents for the treatment of Fe overload disease. We have investigated the mechanisms responsible for their high activity. X-ray crystallography studies show that the tridentate chelate 2-pyridylcarbaldehyde isonicotinoylhydrazone undergoes an unexpected oxidation to isonicotinoyl(picolinoyl)hydrazine when complexed with FeIII. In contrast, in the absence of FeIII, the parent hydrazone is not oxidized in aerobic aqueous solution. To examine whether the diacylhydrazine could be responsible for the biological effects of 2-pyridylcarbaldehyde isonicotinoylhydrazone, their Fe chelation efficacy was compared. In contrast to its parent hydrazone, the diacylhydrazine showed little Fe chelation activity. Potentiometric titrations suggested that this might be because the diacylhydrazine was charged at physiological pH, hindering its access across membranes to intracellular Fe pools. In contrast, the Fe complex of this diacylhydrazine was charge neutral, which may allow facile movement through membranes. These data allow a model of Fe chelation for this compound to be proposed: the parent aroylhydrazone diffuses through cell membranes to bind Fe and is subsequently oxidized to the diacylhydrazine complex which then diffuses from the cell. Other diacylhydrazine analogues that were charge neutral at physiological pH demonstrated high Fe chelation efficacy. Thus, for this class of ligands, the charge of the chelator appears to be an important factor for determining their ability to access intracellular Fe. The results of this study are significant for understanding the biological activity of 2-pyridylcarbaldehyde isonicotinoylhydrazone and for the design of novel diacylhydrazine chelators for clinical use.     

Synthesis of imidacloprid derivatives with a chiral alkylated imidazolidine ring and evaluation of their insecticidal activity and affinity to the nicotinic acetylcholine receptor

A series of imidacloprid (IMI) derivatives with an alkylated imidazolidine ring were asymmetrically synthesized to evaluate their insecticidal activity against adult female housefly, Musca domestica, and affinity to the nicotinic acetylcholine receptor of the flies. The bulkier the alkyl group, the lower was the receptor affinity, but the derivatives methylated and ethylated at the R-5-position of the imidazolidine ring were equipotent to the unsubstituted compound. Quantitative structure–activity relationship (QSAR) analysis of the receptor affinity demonstrated that the introduction of a substituent into the imidazolidine ring was fundamentally disadvantageous, but the introduction of a substituent at the R-5-position was permissible in the case of its small size. The binding model of the synthesized derivatives with the receptor supported the QSAR analysis, indicating the existence of space for a short alkyl group around the R-5-position in the ligand-binding site. In addition, positive correlation was observed between the insecticidal activity and receptor affinity, suggesting that the receptor affinity was the primary factor in influencing the insecticidal activity even if the imidazolidine ring was modified.     

Synthesis of Novel (9S)‐Acyloxy Derivatives of Quinidine and Dihydroquinidine as Insecticidal Agents

Endeavor to discover biorational natural products‐based insecticides, two series (30) of novel (9S)‐acyloxy derivatives of quinidine and dihydroquinidine were prepared and assessed for their insecticidal activity against Mythimna separata in vivo by the leaf‐dipping method at 1 mg/mL. Among all the compounds, especially four derivatives exhibited the best insecticidal activity with final mortality rates of 71.4 %, 75.0 %, 71.4 %, and 75.0 %, respectively. Relatively speaking, 9‐hydroxy group is well tolerated, and the results showed that after modification of the hydroxy group with an acyloxy group, the insecticidal activity was significantly increased; the configuration at C8/9 position is important for insecticidal activity, and the (9S)‐configuration is optimal; modification of the out‐ring double bond is acceptable, and hydrogenation of the double bond enhances insecticidal activity. These preliminary results will pave the way for further modification of quinidine in the development of potential new insecticides.     

Synthesis and insecticidal activity of N-oxydihydropyrroles: 4-hydroxy-3-mesityl-5,5-dimethyl derivatives with various substituents at the 1-position

A new series of N-oxydihydropyrrole derivatives was synthesized and evaluated for insecticidal activity against Nilaparvata lugens and Myzus persicae. Various substituents were introduced to the 1-position of the dihydropyrrole ring, and the derivatives obtained exhibited systemic and/or contact insecticidal activity. The structure-activity relationship revealed that small alkyoxy and alkoxyalkoxy groups were more favorable than alkylcarbonyloxy, alkoxycarbonyloxy, or sulfonyloxy groups as substituents at the 1-position.     

Synthesis and insecticidal activity of novel N-oxydihydropyrroles: 4-hydroxy-3-mesityl-1-methoxymethoxy derivatives with various substituents at the 5-position

This paper reports the synthesis and insecticidal activity of a series of novel 4-hydroxy-3-mesityl-1-methoxymethoxy-1,5-dihydro-2H-pyrrol-2-one derivatives, in which the substituents at the 5-position were varied with a number of alkyl and spirocycloalkyl groups. Investigation of the structure-activity relationships revealed that small alkyl and spirocyclohexyl groups had a favorable effect on the insecticidal activity of these agents against Myzus persicae.     

Synthesis and Biological Activity of O,O-Dialkyl S-(5-Aryl-l,3,4-oxadiazol-2(3H)-on-3-yl)methyl Phosphorothioates and Phosphorodithioates

Some phosphorus derivatives of oxadiazoles were synthesized to seek insecticidal lead compounds. The l,3,4-oxadiazol-2-ones were converted via the N-methylol derivatives to the corresponding N-chloromethyl derivatives. From these derivatives a variety of O,O-dimethyl phosphorodithioates 4, O,O-dimethyl phosphorothioates 5 and O,O-di-i-propyl phosphorothioates 6 were prepared.

These phosphorus derivatives were examined for insecticidal activity towards houseflies and for anti-acetylcholinesterase (anti-AChE) activity using the housefly heads as an enzyme source. Most of the compounds 4 and 5 showed contact toxicity as high as the analogous methidathion insecticides, which appeared to correlate with the strong anti-AChE activity. On the other hand, all the compounds 6 showed a high activity in AChE inhibition but only a poor insecticidal activity.     

Semisynthesis and insecticidal bioactivities of benzoxazole and benzoxazolone derivatives of honokiol,a naturally occurring neolignan derived from Magnolia officinalis

Honokiol, a natural bioactive neolignan isolated from the bark and leaf of Magnolia officinalis and Magnolia obovata, exhibits many important biological properties. In continuation of our interest in discovery of the agrochemicals derived from the natural sources, thirty-seven new 8/8′-alkylthiol-benzoxazole and N-alkyl/sulfonyl-benzoxazolone derivatives of honokiol were prepared and their insecticidal activities were evaluated against the larvae of Mythimna separata Walker and Plutella xylostella Linnaeus. The results showed that eleven derivatives exhibited potent insecticidal activity against M. separata when compared with the positive control. Particularly, compound 5h displayed the most promising insecticidal activity against M. separata with the final mortality rate (FMR) of 58.6%. Meanwhile, compounds 7n (FMR = 65.3%), 7p (FMR = 61.5%), and 8c (FMR = 65.3%) demonstrated a greater insecticidal activity against P. xylostella than toosendanin, a well-known botanical insecticide. Additionally, the preliminary structure-activity relationships (SARs) were also discussed. This study indicates that these honokiol derivatives could be used as leads for the further derivation and development of the potential pesticide candidates for crop protection.     

Two unusual rotenoid derivatives, 7a-O-methyl-12a-hydroxydeguelol and spiro-13-homo-13-oxaelliptone, from the seeds of Derris trifoliata

The crude methanol extract of the seeds of Derris trifoliata showed potent and dose dependent larvicidal activity against the 2nd instar larvae of Aedes aegypti. From this extract two unusual rotenoid derivatives, a rotenoloid (named 7a-O-methyl-12a-hydroxydeguelol) and a spirohomooxarotenoid (named spiro-13-homo-13-oxaelliptone), were isolated and characterised. In addition a rare natural chromanone (6,7-dimethoxy-4-chromanone) and the known rotenoids rotenone, tephrosin and dehydrodeguelin were identified. The structures were assigned on the basis of spectroscopic evidence. The larvicidal activity of the crude extract is mainly due to rotenone.     

Regioselective synthesis of fraxinellone-based hydrazone derivatives as insecticidal agents

In continuation of our program aimed at the discovery and development of natural products-based insecticidal agents, twenty-three new fraxinellone-based hydrazone derivatives were smoothly prepared from fraxinellone via regioselectively allylic oxidation in the presence of selenium dioxide or chromium trioxide under microwave irradiation and subsequent condensation with hydrazides or hydrazines. Their insecticidal activity was evaluated against the pre-third-instar larvae of Mythimna separata Walker in vivo. Especially compounds 6d and 7a displayed the most pronounced insecticidal activity compared with toosendanin, a commercial botanical insecticide derived from Melia azedarach.     

Natural products-based insecticidal agents 7. Semisynthesis and insecticidal activity of novel 4α-alkyloxy-2-chloropodophyllotoxin derivatives against Mythimna separata Walker in vivo

In continuation of our program aimed at the discovery and development of natural products-based insecticidal agents, 16 novel 4α-alkyloxy-2-chloropodophyllotoxin derivatives were semisynthesized from podophyllotoxin, and preliminarily evaluated for their insecticidal activity against the pre-third-instar larvae of Mythimna separata Walker in vivo. Among all the tested derivatives, especially compounds 4b, 4e, 4g, and 4p exhibited more promising and pronounced insecticidal activity than toosendanin, a commercial insecticide derived from Melia azedarach. Generally, it was obviously demonstrated that the length of straight-chain or branched-chain alkyloxy, and heteroatom-containing cycloalkyloxy at the C-4 position of 2-chloropodophyllotoxin were very important for the insecticidal activity.     

Crown-capped imidacloprid: A novel design and insecticidal activity

Imidacloprid (IMI) derivatives conjugated with benzo-15-crown-5 and benzo-18-crown-6 structures, applied for the first time to explore novel insecticidal molecule, elicited strong excitatory toxic signs to the house flies and stunningly exhibited three to five times higher insecticidal activity than that of the parent IMI, yet the two benzo-crown structures themselves had no effect.     

Discovery of a new insecticide lead by optimizing a target-diverse scaffold: tetrazolinone derivatives

In order to discover lead compounds with novel action mechanism, a series of tetrazolinone derivatives bearing structurally diverse substituents, 1-aryl-4-substituted-1,4-di-hydro-5H-tetrazol-5-ones 2, 1-((5-(alkylthio)-1,3,4-oxadiazol-2-yl)methyl)-4-(substituted)- phenyl-1H-tetrazol-5(4H)-ones 5, and 1-((5-(alkylthio)-1,3,4-thiadiazol-2-yl)methyl)-4- (substituted)phenyl-1H-tetrazol-5(4H)-ones 7, were designed and synthesized in good yields by a multiple-step synthetic procedure. The results of greenhouse in vivo test indicated that all the target compounds did not displayed herbicidal activity, however, some of them exhibited excellent in vivo insecticidal activity against Tetranychus cinnabarinus at the concentration of 250 mg L-1. To our knowledge, this is the first report about the insecticidal activity of tetrazolinone derivatives, which indicated that the tetrazolinone scaffold could be identified as a novel insecticidal lead structure. The present work demonstrated that optimizing a target-diverse scaffold is an effective way to discover new lead compounds with new action mechanism or biological activity.     

Natural products-based insecticidal agents 6. Design,semisynthesis, and insecticidal activity of novel monomethyl phthalate derivatives of podophyllotoxin against Mythimna separata Walker in vivo

To discover the more potent analogs, 12 novel monomethyl phthalate derivatives of podophyllotoxin were synthesized and preliminarily tested against the pre-third-instar larvae of Mythimna separata Walker in vivo at the concentration of 1 mg/mL. Compounds 8e–i showed the higher insecticidal activity than podophyllotoxin. Especially 8g exhibited the most potent insecticidal activity compared with toosendanin, a commercially available insecticide derived from Melia azedarach. The structure–activity relationships demonstrated that trans-lactone, 4β-substitution, 2β-chlorine substitution, and 4′-methoxy group were the important structural properties of podophyllotoxins for good insecticidal activity.     

Affinity to the nicotinic acetylcholine receptor and insecticidal activity of chiral imidacloprid derivatives with a methylated imidazolidine ring

Four imidacloprid derivatives with an asymmetrically methylated imidazolidine ring were synthesized. Their affinity to the nicotinic acetylcholine receptor of housefly Musca domestica and insecticidal activity against the housefly were measured. The compound with a 5R-methylated imidazolidine ring demonstrated intrinsic activity comparable to that of the unsubstituted compound. Most of the compounds were synergized by oxygenase inhibitors.     

Natural products-based insecticidal agents 11. Synthesis and insecticidal activity of novel 4α-arylsulfonyloxybenzyloxy-2β-chloropodophyllotoxin derivatives against Mythimna separata Walker in vivo

In continuation of our program aimed at the discovery and development of natural products-based insecticidal agents, 14 novel 4α-arylsulfonyloxybenzyloxy-2β-chloropodophyllotoxin derivatives were stereoselectively semisynthesized from podophyllotoxin, and preliminarily evaluated for their insecticidal activity against the pre-third-instar larvae of Mythimna separata Walker in vivo. Especially compounds 9c' and 9g' exhibited the most promising and pronounced insecticidal activity than toosendanin, a commercial insecticide derived from Melia azedarach at 1mg/mL. Generally, it was preliminarily demonstrated that arylsulfonyloxy groups at the C-2 position of benzyloxy moiety and the length of the side chain on the benzenesulfonyloxy group of 4α-arylsulfonyloxybenzyloxy-2β-chloropodophyllotoxins might be important for the insecticidal activity.     

Natural-product-based insecticidal agents 14. Semisynthesis and insecticidal activity of new piperine-based hydrazone derivatives against Mythimna separata Walker in vivo

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, twenty-six new piperine-based hydrazone derivatives were synthesized from piperine, an alkaloid isolated from Piper nigrum Linn. The single-crystal structures of 6c, 6q and 6w were unambiguously confirmed by X-ray crystallography. Their insecticidal activity was evaluated against the pre-third-instar larvae of Mythimna separata Walker in vivo. Especially compounds 6b, 6i and 6r, the final mortality rates of which, at the concentration of 1 mg/mL, were 62.1%, 65.5% and 65.5%, respectively, exhibited more pronounced insecticidal activity compared to toosendanin at 1 mg/mL, a commercial botanical insecticide isolated from Melia azedarach. It suggested that introduction of the substituents at the C-2 position on the phenyl ring of the hydrazone derivatives was important for their insecticidal activity.     

Insecticidal heterolignans—Tubuline polymerization inhibitors with activity against chewing pests

Starting from natural product podophyllotoxin 1 substituted heterolignans were identified with promising insecticidal in vivo activity. The impact of substitution in each segment of the core structure was investigated in a detailed SAR study, and variation of substituents in both aromatic moieties afforded derivatives 5 and 43 with broad insecticidal activity against lepidopteran and coleopteran species. In vitro measurements supported by modeling studies indicate that heterolignans 3–134 act as tubuline polymerization inhibitors interacting with the colchicine-binding site. Insect specific structure–activity effects were observed showing that the insecticidal SAR described herein differs from reported cytotoxicity studies.