Longifolene-Derived Primary Amine Carboxylates for Sustainable Weed Management: Synthesis and Herbicidal Activity

Twelve novel longifolene-derived primary amine carboxylates were synthesized and evaluated for herbicidal activity. The structures of title compounds were confirmed by Fourier-transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR), 13C NMR, and high-resolution mass spectrometry. The results showed that all the synthesized compounds exhibited higher herbicidal activity than the corresponding carboxylic acids involved in the reaction and the commercial herbicide glyphosate; some of them even possessed inhibition rates of 100% against Lolium multiflorum Lam. and Brassica campestris at low concentrations (0.039–0.313 mmol/L). Moreover, structural factors, including types of carboxylates and carbon chain length, had a great influence on the herbicidal performance. The herbicidal activity of dicarboxylates was similar to or much higher than that of corresponding monocarboxylates and glyphosate. Furthermore, compound 5l was found to be the most active candidate against the root and shoot growth of L. multiflorum Lam. and B. campestris with half maximal inhibitory concentrations (IC50) of around 0.010 and 0.023 mmol/L. The present work indicated that those prepared compounds have great potential to serve as high-performance botanical herbicides used at low doses.