An efficient method has been developed for the synthesis of α-deuterated α-amino esters via hydrogen isotope exchange of α-amino esters in D2O with 2-hydroxynicotinaldehyde as a catalyst under mild conditions. This methodology exhibits a wide range of substrate scopes, remarkable functional group tolerance, and affording the desired products in good yields with excellent deuterium incorporation. Notably, the ortho-hydroxyl group and the pyridine ring of the catalyst play a crucial role in the catalytic activity, which not only stabilizes the carbon-anion intermediates but also enhances the acidity of the amino esters’ α–C–H bond.
Summary Pymetrozine is a synthetic pesticide that can be utilized as the sole carbon source by Pseudomonas sp. strain BYT-1. However, the genes involved in the degradation of pymetrozine remain unknown. We used transposon mutagenesis to create a mutant that unable to hydrolyze pymetrozine. The transposon interrupted the gene pyzH , which was cloned by self-formed adaptor PCR. PyzH hydrolyzed the C=N double bond of pymetrozine to produce 4-amino-6-methyl-4,5-dihydro-2 H -[1,2,4]triazin-3-one (AMDT) and nicotinaldehyde; the latter inhibits PyzH activity. PyzH can completely hydrolyze pymetrozine in the presence of dehydrogenase ORF6, which can convert nicotinaldehyde into nicotinic acid and relieve the inhibition. H 2 18 O-labeling experiments showed that the oxygen atom of nicotinaldehyde came from water instead of oxygen. PyzH homologous genes were also found in other soil isolates able to degrade pymetrozine.
Replacing old pesticides with new pesticide varieties has been the main means to solve pesticide resistance. Therefore, it is necessary to research and develop new antifungal agents for plant protection. In this study, a series of pyridinecarbaldehyde phenylhydrazone derivatives were designed and evaluated for their inhibition activity on plant pathogenic fungi to search for novel fungicide candidates. Picolinaldehyde phenylhydrazone (1) and nicotinaldehyde phenylhydrazone (2) were identified as promising antifungal lead scaffolds. The 4-fluorophenylhydrazone derivatives (1a and 2a) of 1 and 2 showed highly effective and broad-spectrum inhibition activity in vitro on 11 phytopathogenic fungi with EC50 values of 0.870–3.26 μg/mL, superior to the positive control carbendazim in most cases. The presence of the 4-fluorine atom on the phenyl showed a remarkable activity enhancement effect. Compound 1a at 300 μg/mL provided almost complete protection against infection of Alternaria solani on tomatoes over the post-treatment 9 days and high safety to germination of plant seeds. Furthermore, 1a showed strong inhibition activity with an IC50 value of 0.506 μg/mL on succinate dehydrogenase in A. solani. Molecular docking showed that both 1a and 2a can well bind to the ubiquinone-binding region of SDH by the conventional hydrogen bond, carbon–hydrogen bond, π–π or π–amide interaction, π–alkyl interaction, X---F (X = N, C, or H) interaction, and van der Waal forces. Meanwhile, scanning and transmission electron analysis displayed that 1a destroyed the morphology of mycelium and the structure of the cell membrane of A. solani. Fluorescent staining analysis revealed that 1a changed the mitochondrial membrane potential and cell membrane permeability. Thus, pyridinecarbaldehyde phenylhydrazone compounds emerged as novel antifungal lead scaffolds, and 1a and 2a can be considered promising candidates for the development of new agricultural fungicides.
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