Spiro Derivatives in the Discovery of New Pesticides: A Research Review

Application of Asymmetric Catalysis in Chiral Pesticide Active Molecule Synthesis

The different configurations of chiral pesticides generally have significant influence on their biological activities. Chiral agrochemicals with high optical purities have become a prominent topic in the research field of new pesticides due to their advantages including lower toxicity, higher efficiency, and reduced residue levels. However, most commercially available pesticides that possess chiral elements are still used in their racemic forms. To date, asymmetric catalysis has emerged as a versatile tool for the enantioselective synthesis of various chiral agrochemicals and novel chiral pesticide active molecules. This perspective provides a comprehensive overview of the applications of diverse asymmetric catalytic approaches in the facile preparation of numerous novel pesticide active molecules, and our own outlook on the future development of this highly active research direction is also presented at the end of this review.

Electrochemical selenylative ipso-annulation of N-benzylacrylamides to construct seleno-azaspiro[4.5]decadienones

Herein, we present the electrochemical synthesis of selenylated azaspiro[4.5]decadienones through domino selenylation/ipso-annulation of N-benzylacrylamides with diselenides. The method showed a wide substrate scope under mild and external oxidant-free reaction conditions, involving the construction of C-Se and C-C bonds. Gram-scale synthesis and further functional group conversion of the product are also demonstrated.

Palladium-Catalyzed Cycloaddition Reactions of π-Allylpalladium 1,4-Dipoles with 1,3,5-Triazinanes: Access to Hexahydropyrimidines, 1,3-Oxazinanes, and 1,5-Diazocanes

Palladium-catalyzed decarboxylation of 5-methylene-1,3-oxazinan-2-ones and 5-methylene-1,3-dioxan-2-ones to generate aza-π-allylpalladium and oxa-π-allylpalladium 1,4-dipoles for [4 + 2] cycloaddition reaction with 1,3,5-triazinanes was developed, affording a wide range of hexahydropyrimidine and 1,3-oxazinane derivatives in good to excellent yields (up to 99%). The acyclic sulfonamido-substituted allylic carbonates as aza-π-allylpalladium 1,4-dipole precursors also apply to the developed synthesized strategy, achieving the synthesis of hexahydropyrimidines. Moreover, the in situ-generated aza-π-allylpalladium 1,4-dipoles undergoing dimeric [4 + 4] cycloaddition were also demonstrated by the construction of 1,5-diazocane derivatives.

Chemodivergent mechanosynthesis of cyclopentenyl and pyrrolinyl spirobarbiturates from unsaturated barbiturates and enamino esters

A novel and interesting controllable spirocyclization of unsaturated barbiturates with enamino esters for the assembly of cyclopentenyl and pyrrolinyl spirobarbiturates has been developed under ball-milling conditions. The present protocol features high chemoselectivity and efficiency, excellent functional group tolerance and mild reaction conditions.

Synthesis and Application of Task-Specific Bimetal-Organic Frameworks in the Synthesis of Biological Active Spiro-Oxindoles

The use of click chemistry as a smart and suitable method for the development of new heterogeneous catalysts is based on metal-organic frameworks as well as the production of organic compounds. The development of the click chemistry method can provide a new strategy to achieve superior properties of MOFs. Here, the two metals Co and Fe are used to create a bimetallic-organic framework. In the following, the click chemistry and postmodification method are well organized and an acidic heterogeneous porous catalyst is developed. This prepared catalyst was used as a highly efficient catalyst for the preparation of new spiro-oxindoles obtained through click chemistry with good to excellent yields (80-94%). This presented catalytic system can compete with the best reported catalytic systems. The findings showed that the presence of Co and Fe metals in the MOF, and the presence of the triazole ring on the catalyst, can increase the catalytic efficiencies. This study offers novel insights into the architecture of Metal-Organic Frameworks (MOFs), click chemistry, and biologically active compounds. Additionally, the research explores the antibacterial properties of the synthesized spiro-oxindoles and catalysts. The findings reveal significant antibacterial activities of the synthesized compounds against S. aureus, MRSA, and E. coli bacteria.

Discovery and optimization of spirocyclic lactams that inhibit acyl-ACP thioesterase

BACKGROUND

There are various methods to control weeds, that represent considerable challenges for farmers around the globe, although applying small molecular compounds is still the most effective and versatile technology to date. In the search for novel chemical entities with new modes-of-action that can control weeds displaying resistance, we have investigated two spirocyclic classes of acyl-ACP thioesterase inhibitors based on X-ray co-crystal structures and subsequent modelling studies.

RESULTS

By exploiting scaffold-hopping and isostere concepts, we were able to identify new spirolactam-based lead structures showing promising activity in vivo against commercially important grass weeds in line with strong target affinity.

CONCLUSION

The present work covers a series of novel herbicidal lead structures that contain a spirocyclic lactam as a structural key feature carrying ortho-substituted benzyl or heteroarylmethylene side chains. These new compounds show good acyl-ACP thioesterase inhibition in line with strong herbicidal activity. Glasshouse trials showed that the spirolactams outlined herein display promising control of grass-weed species in pre-emergence application combined with dose-response windows that enable partial selectivity in wheat and corn. Remarkably, some of the novel acyl-ACP thioesterase-inhibitors showed efficacy against resistant grass weeds such as Alopecurus myosuroides and Lolium spp. on competitive levels compared with commercial standards. © 2024 Society of Chemical Industry.

Decarboxylative Radical Sulfilimination via Photoredox, Copper, and Brønsted Base Catalysis

Sulfilimines, the aza-variants of sulfoxides, are key structural motifs in natural products, pharmaceuticals, and agrochemicals; and sulfilimine synthesis is therefore important in organic chemistry. However, methods for radical sulfilimination remain elusive, and as a result, the structural diversity of currently available sulfilimines is limited. Herein, we report the first protocol for decarboxylative radical sulfilimination reactions between sulfenamides and N-hydroxyphthalimide esters of primary, secondary, and tertiary alkyl carboxylic acids, which were achieved via a combination of photoredox, copper, and Brønsted base catalysis. This novel protocol provided a wide variety of sulfilimines, in addition to serving as an efficient route for the synthesis of S-alkyl/S-aryl homocysteine sulfilimines and S-(4-methylphenyl) homocysteine sulfoximine. Moreover, it could be used for late-stage introduction of a sulfilimine group into structurally complex molecules, thereby avoiding the need to preserve labile organosulfur moieties through multistep synthetic sequences. A mechanism involving photocatalytic substrate transformation and copper-mediated C(sp3 )-S bond formation is proposed.

Synthesis, toxicological and in silico evaluation of novel spiro pyrimidines against Culex pipiens L. referring to chitinase enzyme

The exponential development of resistance to conventional chemical insecticides adds another important motive for the creation of novel insecticidal active agents. One of the keys to meeting this challenge is the exploration of novel classes of insecticidal molecules with different modes of action. Herein, a novel series of spiro pyrimidine derivatives was prepared using some green synthetic methodologies such as microwave irradiation, and sonication under ultrasound waves. Spiro pyrimidine aminonitrile 1 is a key starting material for the synthesis of targets 2-9 by reaction with different carbon electrophiles and nitrogen nucleophiles. The structures of all the newly synthesized compounds were approved using spectral data. The toxicological efficiency and biological impacts of the synthesized spiro pyrimidine derivatives were assessed against Culex pipiens L. larvae. The toxicity of synthesized compounds showed remarkable variations against the C. pipiens larvae. Where, 3, 4 and 2 were the most efficient compounds with LC50 values of 12.43, 16.29 and 21.73 µg/mL, respectively. While 1 was the least potent compound with an LC50 value of 95.18 µg/mL. As well, other compounds were arranged according to LC50 values as follows 5 > 7 > 6 > 9 > 8. In addition, 3 and 4 exhibited significant prolongation of the developmental duration and greatly inhibited adult emergence. Moreover, many morphological deformities were observed in all developmental stages. Furthermore, cytotoxicity of the most effective compounds was assessed against the normal human cells (WI-38) as non-target organisms, where compounds 2, 4 and 3 showed weak to non-toxic effects. The study of binding affinity and correlation between chemical structure and reactivity was carried out using molecular docking study and DFT calculations to investigate their mode of action. This study shed light on promising compounds with larvicidal activity and biological impacts on the C. pipiens life cycle.

Green synthesis and anti-tumor efficacy via inducing pyroptosis of novel 1H-benzo[e]indole-2(3H)-one spirocyclic derivatives

Pyroptosis induction is anticipated to be a new approach to developing anti-tumor medications. A novel class of spirocyclic compounds was designed by hybridization of 1H-Benzo[e]indole-2(3H)-one with 1,4-dihydroquinoline and synthesized through a new green "one-pot" synthesis method using 10 wt% SDS/H2O as a solvent to screen novel tumor cell pyroptosis inducers. The anti-tumor activity of all compounds in vitro was determined by the MTT method, and a fraction of the compounds showed good cell growth inhibitory activity. The quantitative structure-activity relationship models of the compounds were established by artificial intelligence random forest algorithm (R2 = 0.9656 and 0.9747). The ideal compound A9 could, in a concentration-dependent manner, prevent ovarian cancer cells from forming colonies, migrating, and invading. Furthermore, A9 could significantly induce pyroptosis and upregulate the expression of pyroptosis-related proteins GSDME-N, in addition to inducing apoptosis and mediating the expression of apoptosis-related proteins in ovarian cancer cells. A9 (5 mg/kg) significantly reduced tumor volume and weight of ovarian cancer in vivo, decreased caspase-3 expression in tumor tissue, and induced the production of GSDME-N. This study provides a green and efficient atom-economic synthesis method for 1H-Benzo[e]indole-2(3H)-one spirocyclic derivatives and a promising pyroptosis inducer with anti-tumor activity.

Synthesis of Highly Functionalized Spirocycles and Pentafulvene-Containing Dyes Involving 2-(2'-ketoalkyl)-1,3-indandiones

Synthesis of highly functionalized spiro[4.4]nonane and spiro[4.5]decane motifs by the reaction of dimethylacetylenedicarboxylate (DMAD) with 2-(2'-ketoalkyl)-1,3-indandiones and 2-(3'-ketoalkyl)-1,3-indandiones, respectively, has been developed by utilizing a catalytic amount of DABCO. The tertiary hydroxy-containing spiro[4.4]nonane products were converted into fully conjugated pentafulvene π-systems in an acidic medium through dehydration and unprecedented C-C bond rearrangement.

Nickel-Catalyzed 8-Aminoquinoline Directed Reductive Dialkylcyclization/Homodialkylation of Unactivated Alkenes

Chemo and regioselective dialkylation of alkene is an efficient protocol for constructing useful chemicals, but challenges remain in the unrestricted application of alkylating reagents. Alkyl bromide belongs to the easy-to-access and operable alkyl electrophiles that can be used in reductive coupling with alkenes. Here, we reported convenient strategies for dialkylcyclization and homodialkylation of unactivated β,γ- and γ,δ-unsaturated alkenyl amides with 1,3-dibromoalkanes or primary alkyl bromides under nickel-catalyzed reductive conditions that exhibited high regioselectivity and functional-group tolerance.

Oxidative Spirocyclization of β-Furyl Amides for the Assembly of Spiro-γ-butenolide-γ-butyrolactones

The synthesis of heretofore unknown γ-spirobutenolides has been achieved via an m-CPBA-mediated oxidation of β-furyl amides. The reaction employs a tethered amide, ostensibly a poorly reactive carbonyl, as a nontraditional nucleophile resulting in spirolactone formation and concurrent amide cleavage. The transformation exhibits functional group tolerance and compatibility with complex compounds. In situ 1H NMR spectroscopic studies reveal the identities of key intermediates in the oxidation-spirolactonization-oxidation cascade, suggesting a plausible mechanistic pathway. The distinct diastereofaces of the electrophilic butenolide product may be used for diastereoselective cycloaddition and conjugate addition reactions.

Construction of Annulated Spiro[4.4]-nonane-diones via the Tandem [4 + 2]-Cycloaddition/Aromatization Reaction

A method for the synthesis of both symmetric and asymmetric fused spiro[4.4]-nonane-dione derivatives has been developed. It is based on a Diels-Alder reaction of spiro[4.4]nona-2,7-diene-1,6-dione as a dienophile component followed by immediate aromatization of the adduct. An active diene component can be generated using the tetrabromoxylene/NaI system, the 1,3-diphenylisobenzofuran/BF3 system, or substituted cyclones.

Design, synthesis, and biological evaluation of novel spirocyclic compounds as potential anti-glioblastoma agents

Glioblastoma (GBM) is an aggressive brain tumor with extremely limited clinical treatment options. Because of the blood-brain barrier (BBB), it is difficult for anti-GBM drug candidates to enter the brain to exert their therapeutic effects. The spirocyclic skeleton structure exhibits good lipophilicity and permeability, enabling small-molecule compounds to cross the BBB. Herein, we designed and synthesized novel 3-oxetanone-derived spirocyclic compounds containing a spiro[3.4]octane ring and determined their structure-activity relationship for antiproliferation in GBM cells. Among these, the chalcone-spirocycle hybrid 10m/ZS44 exhibited high antiproliferative activity in U251 cells and permeability in vitro. Furthermore, 10m/ZS44 activated the SIRT1/p53-mediated apoptosis pathway to inhibit proliferation in U251 cells, whereas it minimally impaired other cell-death pathways, such as pyroptosis or necroptosis. In a mouse xenograft model, 10m/ZS44 exhibited a substantial inhibitory effect on GBM tumor growth without showing obvious toxicity. Overall, 10m/ZS44 represents a promising spirocyclic compound for the treatment of GBM.

Construction of Spiro[benzo[a]acridine-12,4'-imidazolidine]-2',5'-dione Derivatives via Ring-Opening and Recyclization of Isatins and C-OH Cleavage of 2-Naphthol

An efficient three-component reaction to access spiro[benzo[a]acridine-12,4'-imidazolidine]-2',5'-dione derivatives has been developed through the ring-opening and recyclization process of isatins and dehydroxylation of 2-naphthol, which is different from their conventional reaction modes. Experimental observations suggest that p-toluenesulfonic acid is the key factor that promotes the success of this synthetic strategy. The research provided a novel approach for the construction of spiro compounds from isatins and 2-naphthol in organic synthesis.

Highly Diastereoselective Multicomponent Synthesis of Spirocyclopropyl Oxindoles Enabled by Rare-Earth Metal Salts

The synthesis of polysubstituted spirocyclopropyl oxindoles using a series of rare-earth metal (REM) salts is reported. REMs, in particular Sc(OTf)₃, allowed access to the target compounds by a multicomponent reaction with high diastereoselectivity (≤94:6:0:0). Density functional theory calculations on the model reaction are consistent with the observed selectivity and revealed that the special coordinating capabilities and the oxophilicity of the metal are key factors in inducing the formation of one main diastereoisomer.

Substrate-Controlled Product Divergence in Iron(III)-Catalyzed Reactions of Propargylic Alcohols: Easy Access to Spiro-indenyl 1,4-Benzoxazines and 2-(2,2-Diarylvinyl)quinoxalines

We report herein unprecedented cascade reactions of O-propargyl-N-tosyl-amino phenols with 10 mol% FeCl₃ in DCE at room temperature for 0.67-3 h to form spiro-indenyl 1,4-benzoxazines with 38-89 % yield. Replacing the substrates' oxygen atom by a N-tosylimine group followed by treatment with the same catalyst and solvent at 80 °C produced 2-(2,2-diarylvinyl)quinoxalines in 12-20 h with up to 62 % yield. Mechanistic understanding provided an insight into the transformations. The use of simple substrates and an environmentally benign low-cost catalyst, broad substrate scope and tolerance of diverse functional groups makes the methodology inherently attractive.

Design, Synthesis, Biological Activity Evaluation and Action Mechanism of Myricetin Derivatives Containing Thiazolebisamide

The plant diseases caused by a variety of pathogens such as viruses, bacteria and fungi pose a great threat to global food production and food safety. Therefore, the search for green, efficient and pollution-free pesticides has become an important task. In this article, 23 myricetin derivatives containing thiazolebisamides active groups have been designed and synthesized. Their activities were evaluated by performing in vitro antibacterial and in vivo antiviral assays, microscale thermophoresis (MST) and molecular docking assays. The results of in vivo antiviral assays showed that compounds A4 and A23 exhibited good antiviral activity with EC50 values of 79.0 and 54.1 μg/mL for therapeutic activity and 103.3 and 91.2 μg/mL for protective activity, respectively. The dissociation constants (Kd) values of compounds A4 and A23 against TMV-CP were 0.021 and 0.018 μM, respectively, determined by microscale thermophoresis (MST), which were much smaller than those of the commercial drug ningnanmycin (NNM), which were 2.84 μM. The interaction of compounds A4, A23 with TMV-CP was further verified at the molecular level. In addition, in vitro antifungal assays of this series of compounds showed that they exhibited some inhibitory activity against a variety of fungi, especially against the phytophthora capsici. Among them, A13 and A20 showed similar inhibitory activity to the control drug azoxystrobin at 100 μg/mL against the phytophthora capsici.

Design, synthesis, and biological activity of novel spiro-pyrazolo[1,5-a]quinazolines derivatives as potential insecticides

BACKGROUND

Arylpyrazole insecticides display broad-spectrum insecticidal activity against insect pests. However, the high toxicity toward honeybees associated with fipronil prohibits its agronomic utility. To explore reducing the toxicity of aryl pyrazole analogs to bees, a series of new spiro-pyrazolo[1,5-a]quinazoline derivatives were designed and synthesized.

RESULTS

Bioassay results showed that these compounds exhibited good insecticidal activity. In particular, the insecticidal activity of compound 5f against Plutella xylostella larvae (median lethal contentration, LC₅₀  = 1.43 mg L^-1 ) was equivalent to that of fipronil. Moreover, some compounds also showed good insecticidal activity against Solenopsis invicta. Importantly, the bee toxicity study confirmed that compound 5f had much lower acute oral toxicity, with a median lethal dose (LD₅₀ ) = 1.15 μg bee^-1 that was three to four orders of magnitude greater than that of fipronil (0.0012 μg bee^-1 ). Electrophysiological studies were conducted using honeybee γ-aminobutyric acid receptor heterologously expressed in Xenopus oocytes to explain the reduced bee toxicity of compound 5f. The inhibitory effect of compound 5f (16.29 μmol L^-1 ) was determined to be approximately 700-fold lower than that of fipronil (0.023 μmol L^-1 ).

CONCLUSION

These spiro-pyrazolo[1,5-a]quinazoline derivatives could be potential candidates and lead structures for the discovery of novel insecticides with low bee toxicity. © 2022 Society of Chemical Industry.