Synthesis and Herbicidal Activity of 3-Phenyl-5-oxy-benzothiazole-2-one Derivatives

A series of 3-phenyl-5-oxy-benzothiazole-2-ones were designed based on the structure of 3-(2-pyridyl)-benzothiazol-2-one by using positional isomerization and bioisosteric replacement strategies. Starting from 4-chloro-3-nitroanisole, the title compounds were prepared via cyclization, oxidation, nucleophilic aromatic substitution, demethylation, and O-alkylation reactions. The herbicidal activities of 31 compounds against Echinochloa crus-galli and Portulaca oleracea were evaluated by the Petri dish assay. The results indicated that VI-2, VI-3, VI-4, VIII-13, VIII-14, VIII-15, VIII-16, VIII-18, VIII-19, VIII-24, and VIII-25 completely inhibited the growth of P. oleracea at 10 μg/mL. VIII-18 showed the most potent activity against P. oleracea, and the inhibition rate is 100% even at 1 μg/mL. Barnyard grass is relatively insensitive to most of the test compounds, and only VI-2, VIII-16, and VIII-18 showed a strong inhibitory effect at 10 μg/mL. The herbicidal activities of compounds VIII-13, VIII-18, and VIII-19 against a panel of weeds were further evaluated by pot experiments in glasshouse. The results showed that VIII-13, VIII-18, and VIII-19 exhibited good herbicidal activity against broadleaf weeds such as Abutilon theophrasti, Solanum nigrum, Amaranthus retroflexus, and Chenopodium album at 30 and 15 g/ha, whereas they only showed a moderately inhibitory activity against grass weeds such as E. crus-galli, and Digitaria sanguinalis, as well as geraniaceae weeds like Geranium carolinianum. Concurrently, we employed molecular simulations to obtain further insights into the binding mechanism with NtPPO. In general, 3-phenyl-5-oxy-benzothiazole-2-ones were discovered as a type of promising candidates for the management of broadleaf weeds, and they provide a novel structural scaffold for the development of herbicides.