New Lead Discovery of Herbicide Safener for Metolachlor Based on a Scaffold-Hopping Strategy

The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of the existing herbicides in the field. Sanshools, which are well known as spices, are N-alkyl substituted compounds extracted from the Zanthoxylum species and have several essential physiological and pharmacological functions. Sanshools display excellent safener activity for the herbicide metolachlor in rice seedlings. However, the high cost of sanshools extraction and difficulties in the synthesis of their complicated chemical structures limit their utilization in agricultural fields. Thus, the present study designed and synthesized various N-alkyl amide derivatives via the scaffold-hopping strategy to solve the challenge of complicated structures and find novel potential safeners for the herbicide metolachlor. In total, 33 N-alkyl amide derivatives (2a–k, 3a–k, and 4a–k) were synthesized using amines and saturated and unsaturated fatty acids as starting materials through acylation and condensation. The identity of all the target compounds was well confirmed by 1H-NMR, 13C-NMR, and high-resolution mass spectrometry (HRMS). The primary evaluation of safener activities for the compounds by the agar method indicated that most of the target compounds could protect rice seedlings from injury caused by metolachlor. Notably, compounds 2k and 4k displayed excellent herbicide safener activities on plant height and demonstrated relatively similar activities to the commercialized compound dichlormid. Moreover, we showed that compounds 2k and 4k had higher glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO) activities in rice seedlings, compared to the metolachlor treatment. In particular, 2k and 4k are safer for aquatic organisms than dichlormid. Results from the current work exhibit that compounds 2k and 4k have excellent crop safener activities toward rice and can, thus, be promising candidates for further structural optimization in rice protection.

The Use of Herbicide Safener Increases the Selectivity of Nicosulfuron to Maize Crops

The herbicide nicosulfuron is an important tool for weed control in maize crops; however, its incorrect use can cause yield losses to crops due to its high toxicity. The objective of this work was to evaluate the efficiency of using herbicide safener to increase selectivity of nicosulfuron to maize crops. The experiment was conducted in field conditions, and the treatments consisted of dose-response curves, using nicosulfuron at rates of 0, 15, 30, 45, and 60 g ha-1, applied with safener and/or malathion to maize crops at the V5-V6 stage. The use of organophosphorus insecticides such as malathion decrease the selectivity of nicosulfuron to maize crops. Rates of up to 60 g ha-1 were selective to the maize crops when using nicosulfuron or nicosulfuron + safener. However, plant height decreased 0.19 and 0.91 cm for each gram of nicosulfuron in the treatments nicosulfuron + safener + malathion, and nicosulfuron + malathion, respectively, at 28 days after the application. The phytotoxicity increased 0.19% and 0.97% in the treatments nicosulfuron + safener + malathion and nicosulfuron + malathion, respectively. The number of grains per row and grain yield were affected by the treatments with nicosulfuron + malathion, presenting decreases of 0.09 grains and 52 kg ha-1, respectively. Thus, adding safener to the herbicide mixture increases the selectivity of nicosulfuron to maize crops, decreases damages regarding plant height and phytotoxicity, and prevents effects of the herbicide on the number of grains per row and grain yield, up to the rate of 60 g ha-1.

Crystal structure of fenclorim

In the title compound, C10H6Cl2N2(systematic name: 4,6-dichloro-2-phenylpyrimidine), which is used commercially as the herbicide safener, fenclorim, the dihedral angle between the dichloropyrimidyl and phenyl rings is 9.45 (10)°. In the crystal, C—H...N hydrogen bonds link adjacent molecules, forming chains along thec-axis direction. In addition, weak intermolecular C—Cl...π [3.6185 (10) Å] and π–π [3.8796 (11) Å] interactions are present, forming a three-dimensional network.