Synthesis, insecticidal activity, and ensembled docking of nitroguanidines bearing S- and R-proline

BACKGROUND

The amino acids R- and S-proline were used to synthesize novel neonicotinoid derivatives that, after being characterized by ¹ H, DEPTQ 135, and HRMS-QTOF, were evaluated for use as insecticides against Galleria mellonella (caterpillar), Sitophilus zeamais, Xylosandrus morigerus, Xyleborus affinis, and Xyleborus ferrugineus.

RESULTS

Comparisons of biological activity and absolute configuration showed that the R enantiomer had excellent and outstanding insecticidal activity against the insects tested, with up to 100% mortality after 12 h compared with dinotefuran at the same concentration.

CONCLUSIONS

The results suggest that compound R6 is an excellent lead enantiopure insecticide for future development in the field of crop protection. Furthermore, intermolecular interactions between nicotinic acetylcholine receptors and the R enantiomer displays a lower score which mean a higher affinity to the nAChR receptor and the π-π interactions are more stable than the S derivative. © 2023 Society of Chemical Industry.

Isolation and Identification of Pennogenin Tetraglycoside from Cestrum nocturnum (Solanaceae) and Its Antifungal Activity against Fusarium kuroshium, Causal Agent of Fusarium Dieback

Antifungal assay-guided fractionation of the methanolic crude extract of Cestrum nocturnum (Solanaceae), popular known as ‘lady of the night’, led the isolation and identification of the steroidal saponin named pennogenin tetraglycoside, which was identified for the first time in this plant species by spectroscopic means. The crude extract, fractions and pennogenin tetraglycoside exhibited mycelial growth inhibition of Fusarium solani and F. kuroshium. F. solani is a cosmopolitan fungal phytopathogen that affects several economically important crops. However, we highlight the antifungal activity displayed by pennogenin tetraglycoside against F. kuroshium, since it is the first plant natural product identified as active for this phytopathogen. This fungus along with its insect symbiont known as Kuroshio shot hole borer (Euwallacea kuroshio) are the causal agents of the plant disease Fusarium dieback that affects more than 300 plant species including avocado (Persea americana) among others of ecological relevance. Scanning electron microscopy showed morphological alterations of the fungal hyphae after exposure with the active fractions and 12 phenolic compounds were also identified by mass spectrometry dereplication as part of potential active molecules present in C. nocturnum leaves.

Synthesis and Insecticidal Evaluation of Chiral Neonicotinoids Analogs: The Laurel Wilt Case

Xyleborus sp beetles are types of ambrosia beetles invasive to the United States and recently also to Mexico. The beetle can carry a fungus responsible for the Laurel Wilt, a vascular lethal disease that can host over 300 tree species, including redbay and avocado. This problem has a great economic and environmental impact. Indeed, synthetic chemists have recently attempted to develop new neonicotinoids. This is also due to severe drug resistance to “classic” insecticides. In this research, a series of neonicotinoids analogs were synthesized, characterized, and evaluated against Xyleborus sp. Most of the target compounds showed good to excellent insecticidal activity. Generally, the cyclic compounds also showed better activity in comparison with open-chain compounds. Compounds R-13, 23, S-29, and 43 showed a mortality percent of up to 73% after 12 h of exposure. These results highlight the enantioenriched compounds with absolute R configuration. The docking results correlated with experimental data which showed both cation-π interactions in relation to the aromatic ring and hydrogen bonds between the search cavity 3C79 and the novel molecules. The results suggest that these sorts of interactions are responsible for high insecticidal activity.

l-Proline as a Valuable Scaffold for the Synthesis of Novel Enantiopure Neonicotinoids Analogs

In this research, six neonicotinoid analogs derived from l-proline were synthesized, characterized, and evaluated as insecticides against Xyleborus affinis. Most of the target compounds showed good to excellent insecticidal activity. To the best of our knowledge, this is the first report dealing with the use of enantiopure l-proline to get neonicotinoids. These results highlighted the compound 9 as an excellent candidate used as the lead chiral insecticide for future development. Additionally, molecular docking with the receptor and compound 9 was carried out to gain insight into its high activity when compared to dinotefuran. Finally, the neurotoxic evaluation of compound 9 showed lower toxicity than the classic neonicotinoid dinotefuran.

Hafnium(IV) Chloride Catalyzes Highly Efficient Acetalization of Carbonyl Compounds

BACKGROUND

Hafnium(IV) tetrachloride efficiently catalyzes the protection of a variety of aldehydes and ketones, including benzophenone, acetophenone, and cyclohexanone, to the corresponding dimethyl acetals and 1,3-dioxolanes, under microwave heating. Substrates possessing acid-labile protecting groups (TBDPS and Boc) chemoselectively generated the corresponding acetal/ketal in excellent yields.

AIMS AND OBJECTIVES

In this study. the selective protection of aldehydes and ketones using a Hafnium(IV) chloride, which is a novel catalyst, under microwave heating was observed. Hence, it is imperative to find suitable conditions to promote the protection reaction in high yields and short reaction times. This study was undertaken not only to find a novel catalyst but also to perform the reaction with substrates bearing acid-labile protecting groups, and study the more challenging ketones as benzophenone.

MATERIALS AND METHODS

Using a microwave synthesis reactor Monowave 400 of Anton Paar, the protection reaction was performed on a raging temperature of 100°C ±1, a pressure of 2.9 bar, and an electric power of 50 W. More than 40 substrates have been screened and protected, not only the aldehydes were protected in high yields but also the more challenging ketones such as benzophenone were protected. All the products were purified by simple flash column chromatography, using silica gel and hexanes/ethyl acetate (90:10) as eluents. Finally, the protected substrates were characterized by NMR 1H, 13C and APCI-HRMS-QTOF.

RESULTS

Preliminary screening allowed us to find that 5 mol % of the catalyst is enough to furnish the protected aldehyde or ketone in up to 99% yield. Also it was found that substrates with a variety of substitutions on the aromatic ring (aldehyde or ketone), that include electron-withdrawing and electrondonating group, can be protected using this methodology in high yields. The more challenging cyclic ketones were also protected in up to 86% yield. It was found that trimethyl orthoformate is a very good additive to obtain the protected acetophenone. Finally, the protection of aldehydes with sensitive functional groups was performed. Indeed, it was found that substrates bearing acid labile groups such as Boc and TBDPS, chemoselectively generated the corresponding acetal/ketal compound while keeping the protective groups intact in up to 73% yield.

CONCLUSION

Hafnium(IV) chloride as a catalyst provides a simple, highly efficient, and general chemoselective methodology for the protection of a variety of structurally diverse aldehydes and ketones. The major advantages offered by this method are: high yields, low catalyst loading, air-stability, and non-toxicity.

Anti-inflammatory Activity of Piperlotines

Abstract. In the present study we evaluated six α,β-unsaturated amides named piperlotines (for being isolated originally from Piper species) as new in vivo anti-inflammatory agents. In addition, we report the mechanosynthesis of two of them by mechanochemical activation of a Horner-Wadsworth-Emmons reaction. The reaction of β-amidophosphonate 4, an aromatic aldehyde and K2CO3 under grinding in a mortar and pestle afforded piperlotines 5-6 in good yields (70-88%) in short reaction times, obtaining only (E)-diastereomer. Piperlotines previously prepared were tested as anti-inflammatory and antibacterial agents. In this respect, derivatives 2 and 6 exhibited excellent in vivo anti-inflammatory activity on mice, especially trough topical administration (TPA acute inflammation model). Furthermore, piperlotine A, and compounds 2 and 6 had slight antimycobacterial activity against Mycobacterium tuberculosis (MIC = 50 µg/mL). In conclusion, the solvent-free mechanosynthesis of piperlotines produced valuable compounds that could serve as templates for further investigation in the search of better drug-like compounds for the treatment of inflammatory diseases.   Resumen. En la presente investigación se evaluó la actividad anti-inflamatoria in vivo de seis amidas α,β-insaturadas, identificadas en la literatura como piperlotinas debido a su inicial aislamiento a partir de especies vegetales del género Piper (como las pimientas). La reacción del β-amidofosfonato 4 con un aldehído aromático y K2CO3 en molienda con mortero y pistilo produjo las piperlotinas 5-6 con buenos rendimientos (70-80%) en tiempos cortos de reacción, obteniendo solamente el diastereoisómero (E). Las piperlotinas preparadas se evaluaron como agentes anti-inflamatorios y antibacterianos, observando excelente actividad anti-inflamatoria para los derivados 2 y 6, especialmente cuando se probaron mediante administración tópica (modelo de inflamación aguda por TPA). Además, la piperlotina A y los derivados 2 y 6 mostraron actividad antibacteriana contra Mycobacterium tuberculosis (MIC = 50 µg/mL). En conclusión, la síntesis de piperlotinas a través de molienda en condiciones libres de disolvente generó importantes productos que pueden ser utilizados como punto de partida para generar nuevos compuestos bioactivos para el tratamiento de padecimientos relacionados con la inflamación.

Identification of Antibacterial Phenolics in Selected Plant Species from Mexican Cloud Forest by Mass Spectrometry Dereplication

Fifteen plant species from a protected cloud forest (CF) in Veracruz, Mexico, were screened for their in vitro capacity to inhibit the growth of the phytopathogenic bacteria Chryseobacterium sp., Pseudomonas cichorii, Pectobacterium carotovorum and Pantoea stewartii, causal agents of damage to crops like 'chayote', lettuce, potato and corn. As a result, the bioactivity of Turpinia insignis and Leandra cornoides is reported for the first time against Chryseobacterium sp. and P. cichorii. In addition, 24 and 18 compounds not described for these species were dereplicated by an UPLC/MS-MS method, respectively. The identified compounds included simple phenols, hydroxycinnamic acids, flavonoids and coumarins. The antibacterial assay of 12 of them demonstrated the bacteriostatic effect of vanillin, trans-cinnamic acid, scopoletin and umbelliferone against Chryseobacterium sp. These findings confirm for the first time the value of the CF plants from Veracruz as sources of bioactive natural products with antimicrobial properties against phytopathogenic bacteria.

Sesquiterpene Lactones and Phenols from Polyfollicles of Magnolia vovidessi and their Antimicrobial Activity

Bioassay-guided fractionation of an active crude extract (EtOAc) of polyfollicles of Magnolia vovidessi, an endemic medicinal plant of the cloud forest of Mexico, led to the isolation and identification of shizukolidol (1), an eudesmane-type sesquiterpenoid lactone that showed antibacterial activity against the economically important phytopathogenic bacterium Chryseobacterium sp. (MIC= 400 μg/mL). In addition, 4α,8β-dihydroxy-5α(H)-eudesm-7(11)-en-8,12-olide 8 (2), rutin, scopoline and scopoletine were also isolated as were mexicanin, parthenolide, costunolide, astragalin, quercetin, hesperidin, p-coumaric acid, chlorogenic acid, vanillin, vanillic acid, 4-hydroxybenzoic acid, protocatechuic acid and shikimic acid identified by a dereplication-like procedure using LC-ESI-MS/MS. Rutin displayed mild anti-oomicite activity against phytopathogen Phytophthora cinnamomi.