Bioassays against pinewood nematode: assessment of a suitable dilution agent and screening for bioactive essential oils

Acetone was investigated and found to be an appropriate alternative to Triton X-100 as a solvent of essential oils in bioassays aimed to investigate their effects on pinewood nematode (Bursaphelenchus xylophilus) mortality. Therefore it was used as dilution agent to screen the effectiveness of fifty two essential oils against this pest. Thirteen essential oils were highly effective, resulting in more than 90% pinewood nematode mortality at 2 mg/mL, with six of them resulting in 100% mortality. LC100 values ranged between 0.50 mg/mL and 0.83 mg/mL for the essential oils of Origanum vulgare and Satureja montana, respectively. Essential oils were submitted to gas chromatography and gas chromatography-mass spectrometry analysis and their chemical composition established. Data from essential oils with 100% mortality at 2 mg/mL and other essential oils previously found to have LC100 ≤ 2 mg/mL was combined, their chemical profiles investigated by correspondences analysis plus automatic classification.

Design, Synthesis and Bioassays of 3-substituted-3-hydroxyoxindoles for cholinesterase inhibition

Based on the positive bioassay results of the known oxindole hit compound rac-1-benzyl-3-hydroxy-3-phenylindolin-2-one which showed significant inhibition of butyrylcholinesterase (BuChE) (IC50=7.41 μM), a library of 31 analogues of 3-substituted-3-hydroxyoxindoles was synthesized and screened for both acetylcholinesterase (AChE) and BuChE activity. Our bioassays revealed that some of the new compounds exhibited moderate inhibition of eel AChE (EeAChE) and very good inhibition of equine serum BuChE (EqBuChE) with a best IC50 of 1.02 μM. On the basis of these results, the lead compound 1-((1-benzylpiperidin-4-yl)methyl)-3-hydroxy-3-phenylindolin-2-one was designed, which was shown to interact well with the enzymes active sites by molecular docking, was synthesized and upon bioassay gave an IC50 of 6.61 μM for BuChE. Interestingly, when we separated rac-benzyl-3-hydroxy-3-phenylindolin-2-one into the individual enantiomers (R)- and (S)-benzyl-3-hydroxy-3-phenylindolin-2-one it was the latter enantiomer that gave the best IC50 of 6.19 μM for BuChE.

First report on Meloidogyne chitwoodi hatching inhibition activity of essential oils and essential oils fractions

The Columbia root-knot nematode (CRKN), Meloidogyne chitwoodi, is an EPPO A2 type quarantine pest since 1998. This nematode causes severe damage in economically important crops such as potato and tomato, making agricultural products unacceptable for the fresh market and food processing. Commonly used nematicidal synthetic chemicals are often environmentally unsafe. Essential oils (EOs) may constitute safer alternatives against RKN. EOs, isolated from 56 plant samples, were tested against CRKN hatching, in direct contact bioassays. Some of the most successful EOs were fractionated and the hydrocarbon molecules (HM) and oxygen-containing molecules (OCM) fractions tested separately. 24 EOs displayed very strong hatching inhibitions (≥90 %) at 2 µL mL−1 and were further tested at lower concentrations. Dysphaniaambrosioides, Filipendula ulmaria, Ruta graveolens, Satureja montana and Thymbra capitata EOs revealed the lowest EC50 values (<0.15 µL mL−1). The main compounds of these EOs, namely 2-undecanone, ascaridol, carvacrol, isoascaridol, methyl salicylate, p-cymene and/or γ-terpinene, were putatively considered responsible for CRKN hatching inhibition. S. montana and T. capitata OCM fractions showed hatching inhibitions higher than HM fractions. The comparison of EO and corresponding fractions EC50 values suggests interactions between OCM and HM fractions against CRKN hatching. These species EOs showed to be potential environmentally friendly CRKN hatching inhibitors; nonetheless, bioactivity should be considered globally, since its HM and OCM fractions may contribute, diversely, to the full anti-hatching activity.