Chemistry and Biology of Podophyllotoxins: An Update

Cloning and bioinformatics analysis of key gene ShOMT3 of podophyllotoxin biosynthesis pathway in Sinopodophyllum hexandrum

Sinopodophyllum hexandrum (S. hexandrum) is an endangered traditional Chinese medicine as abundant podophyllotoxin with powerful anticancer activity. In this study, the rootstalks of S. hexandrum from different geographical locations in China [S1 (Gansu) and S2 (Shaanxi)] were used as research materials to clone the key gene pluviatolide O-methyltransferase 3 (ShOMT3) in the podophyllotoxin biosynthetic pathway. Subsequently, bioinformatics analysis of the ShOMT3 gene and its encoded protein was subjected to bioinformatics analysis using various analysis software including ProtParam, DeepTMHMM, SubLoc, Signal-P 5.0, and Swiss-model. The results of the analysis revealed that the CDS region of the ShOMT3 gene is 1119 bp long, encoding 372 amino acids. The theoretical molecular weight of the ShOMT3 protein is 41.32784 kD, and the theoretical isoelectric point (pI) is 5.27. The instability coefficient of the protein is 46.05, the aliphatic index is 93.58, and the grand average of hydropathicity (GRAVY) is 0.037, indicating that it is an unstable hydrophobic protein. The protein does not contain transmembrane domains or signal peptides, indicating that it is a non-secreted protein. Secondary structure prediction results suggests that the protein consists of alpha helices, random coils, extended strands, and beta-turns. Tertiary structure prediction results suggests that the protein functions as a monomer. In the phylogenetic tree, the ShOMT3 protein has the highest homology with Podophyllum peltatum (P. peltatum). The successful cloning and bioinformatics analysis of the ShOMT3 gene provide theoretical basis and excellent genetic resources for the molecular regulatory mechanism analysis of the podophyllotoxin biosynthetic pathway and molecular breeding in S. hexandrum.

Structural Optimization of Natural Plant Products: Construction, Pesticidal Activities, and Toxicology Study of New 2-Isopropanol-4-methoxy-7-alkyl/aryloxycarbonyl-(E)-vinyl-2,3-dihydrobenzofurans

Recently, the structural optimization of natural bioactive products has been one of the important ways to discover new pesticide candidates. Based on osthole as a lead compound, herein, a series of new 2-isopropanol-4-methoxy-7-alkyl/aryloxycarbonyl-(E)-vinyl-2,3-dihydrobenzofuran derivatives were synthesized. Steric configurations of compounds 3, 4, 6, 9, 11, 29, and 31 were confirmed by X-ray monocrystallography. Notably, an efficient method for preparation of 2-isopropanol-2,3-dihydrobenzofurans from osthole by the epoxidation and rearrangement reactions was developed. Against Plutella xylostella Linnaeus, compound 31 (R = CH2CH2Ph; LC50: 0.759 mg/mL) displayed a 1.9-fold insecticidal activity compared to that of osthole; against Tetranychus cinnabarinus Boisduval, compound 34 (R = (CH2)9CH3; LC50: 0.401 mg/mL) exhibited a 3.3-fold acaricidal activity and good control effects compared to those of osthole. By the scanning electron microscope (SEM) imaging method, it was demonstrated that the acaricidal activity of compound 34 may be related to the damage of the cuticle layer crest of T. cinnabarinus. Compound 34 could be further studied as a potential acaricide.

Modular Assembly of Heterotrifunctional Molecules Enabled by Iodosulfonylation of Allenes and Subsequent Amination

Beyond the rapid achievements of therapeutic heterobifunctional molecules, some recent efforts have focused on constructing heterotrifunctional molecules, aiming at developing more potent and selective therapeutic agents or emerging additional functions to heterobifunctional molecules. However, the synthesis of these complex molecules requires a specific design and lengthy steps. We have developed a two-step strategy for the modular construction of heterotrifunctional molecules, enabled by the sustainable and convenient iodosulfonylation of allenes followed by SN2'-selective amination. This strategy successfully incorporates a broad range of biologically active molecules, labeling them with a fluorescent group. The applications of the obtained compounds in selective protein labeling, subcellular imaging, and targeted inhibition of tumor cells make this strategy highly appealing.

Plant natural product-based pesticides in crop protection: semi-synthesis, mono-crystal structures and agrochemical activities of osthole ester derivatives, and study of their toxicology against Tetranychus cinnabarinus (Boisduval)

BACKGROUND

Owing to large amounts of synthetic pesticides being extensively and unreasonably used for crop protection, currently, resistance and negative impacts on human health and environment safety have appeared. Therefore, development of potential pesticide candidates is highly urgent. Herein, a series of ester derivatives of osthole were designed and synthesized as pesticidal agents.

RESULTS

Six spatial configurations of 4'-(p-toluenoyloxy)osthole (4b), 4'-(m-fluorobenzoyloxy)osthole (4f), 4'-(p-fluorophenylacetyloxy)osthole (4m), 4'-(3'',4''-methylenedioxybenzoyloxy)osthole (4q), 4'-formyloxyosthole (4u) and 4'-acetyloxyosthole (4v) were determined by X-ray mono-crystal diffraction. Compounds 4b, 4'-(p-chlorobenzoyloxy)osthole (4g), 4'-(m-chlorobenzoyloxy)osthole (4h), 4'-(p-bromobenzoyloxy)osthole (4i) and 4'-(2''-chloropyridin-3''-ylcarbonyloxy)osthole (4p) showed higher insecticidal activity than toosendanin against Mythimna separata Walker; notably, compound 4b displayed 1.8 times insecticidal activity of the precursor osthole. Against Tetranychus cinnabarinus Boisduval, compounds 4g and 4h showed 3.3 and 2.6 times acaricidal activity of osthole, and good control effects in the glasshouse. Scanning electron microscopy assay demonstrated that compound 4g can damage the cuticle layer of T. cinnabarinus resulting in death.

CONCLUSION

Compounds 4g and 4h can be further studied as lead pesticidal agents for the management of M. separata and T. cinnabarinus. These results will pave the way for application of osthole derivatives as agrochemicals. © 2024 Society of Chemical Industry.

Computational Study Into the Oxidative Ring-Closure Mechanism During the Biosynthesis of Deoxypodophyllotoxin

The nonheme iron dioxygenase deoxypodophyllotoxin synthase performs an oxidative ring-closure reaction as part of natural product synthesis in plants. How the enzyme enables the oxidative ring-closure reaction of (-)-yatein and avoids substrate hydroxylation remains unknown. To gain insight into the reaction mechanism and understand the details of the pathways leading to products and by-products we performed a comprehensive computational study. The work shows that substrate is bound tightly into the substrate binding pocket with the C7'-H bond closest to the iron(IV)-oxo species. The reaction proceeds through a radical mechanism starting with hydrogen atom abstraction from the C7'-H position followed by ring-closure and a final hydrogen transfer to form iron(II)-water and deoxypodophyllotoxin. Alternative mechanisms including substrate hydroxylation and an electron transfer pathway were explored but found to be higher in energy. The mechanism is guided by electrostatic perturbations of charged residues in the second-coordination sphere that prevent alternative pathways.

Construction and Single-Crystal Structures of N-Isoxazolin-5-ylcarbonylindole Derivatives, and Their Pesticidal Activities and Toxicology Study

To explore natural product-based pesticide candidates, a series of indole derivatives containing the isoxazoline skeleton at the N-1 position were synthesized by 1,3-dipolar [2 + 3] cycloaddition reaction. Their structures were characterized by melting points (mp), infrared (IR) spectra, proton nuclear magnetic resonance spectra (1H NMR), carbon-13 nuclear magnetic resonance spectra (13C NMR), and high resolution mass spectrometry (HRMS). The single-crystal structures of five compounds were presented. Against Tetranychus cinnabarinus Boisduval, compound 3b showed greater than 3.8-fold acaricidal activity of indole and good control effects under glasshouse conditions. Against Aphis citricola Van der Goot, compounds 3b and 3q exhibited 48.3- and 36.8-fold aphicidal activity of indole and 6-methylindole, respectively. Particularly, compound 3b showed good bioactivities against T. cinnabarinus and A. citricola. Against Eriosoma lanigerum Hausmann, compound 3h and 3i showed 2.1 and 1.9 times higher aphicidal activity compared to indole. Furthermore, the construction of the epidermal cuticle layer of 3b-treated carmine spider mites was distinctly damaged, which ultimately led to their death.