High value-added application of rosin as a potential renewable source for the synthesis of acrylopimaric acid-based botanical herbicides

Abstract

Turning natural products into value-added herbicide preparation is an alternative to synthetic compounds for environmentally friendly weed management. In continuation of our research on rosin-based herbicidal agents, 33 acrylopimaric acid (APA) derivatives were synthesized, and were structurally characterized using proton nuclear magnetic resonance, elemental analysis, electrospray ionization mass spectra, melting point, infrared spectroscopy, and X-ray crystallography. In addition, the herbicidal activity of APA derivatives against Amaranthus retroflexus, Echinochloa crus-galli, and Brassica campestris L. were investigated. Among the APA derivatives, the diacylthiourea compounds 3a–f showed significant post-emergence herbicidal activity against E. crus-galli. Moreover, compounds 3b–d (with EC50 values of 13.191, 13.441, and 13.191gai/ha, respectively) displayed more promising herbicidal activity against E. crus-galli than sulfentrazone (a commercial herbicide with an EC50 value of 15.606gai/ha). In quantitative structure–activity relationship (QSAR) study, optimal conformers and best multilinear regression analysis were performed using Gaussian and CODESSA software. The four descriptors correlating the molecular structures with their herbicidal activities were as follows: Total Charge, log MS, qNmax and qCmax. The generated QSAR model had a correlation coefficient of 0.9625, a Fisher significance ratio of 185.96, and a squared standard error of the estimates of 0.0012. Preliminary studies on the structure–activity relationship and QSAR showed that the higher electron density around the substituent groups on the nitrogen atoms of rosin-based backbone structure and smaller volume of spatial structure played a beneficial effect on the herbicidal activity. Thus, rosin is a promising source of a value-added product for crop protection.