Toxicity of thymol, carvacrol and their respective phenoxyacetic acids in Lactuca sativa and Sorghum bicolor

Natural and semisynthetic compounds may be useful to obtain novel herbicides. Thymol and carvacrol, which belong to the class of phenols, are examples of molecules found in the nature that present phytotoxic activity. Thus, we aimed to synthesize phenoxyacetic acids from thymol and carvacrol and to use them in plant bioassays. The thymoxyacetic and carvacroxyacetic acids were obtained from thymol and carvacrol, respectively, in the presence of sodium chloroacetate, under reflux, followed by acidification. These compounds were tested against Lactuca saliva and Sorghum bicolor initial seed development and their effects were tested on L. sativa and S. bicolor DNA. We also evaluated the performance of these compounds in the mitotic cycle of meristematic cells of L. saliva roots. The synthesized compounds were characterized by mass spectrometry and nuclear magnetic resonance-spectroscopy (NMR) of H-1 and C-13. The compounds were tested in different concentrations regarding the biological assays: 0.0, 0.375, 0.750, 1.50 and 3.0 mmol L-1. After the analysis of the comet assay, carvacrol and carvacroxyacetic acid showed the most damaging effects on L. sativa and S. bicolor DNA. To corroborate the results found for these two compounds, we carried out an analysis with ISSR to verify the molecular damages in the two tested plants. We concluded that carvacrol, thymol, carvacroxyacetic and thymoxyacetic acids presented phytotoxic and cytotoxic activities. Carvacrol and the carvacroxyacetic acid also showed genotoxic action at the concentration of 3.0 mmol L-1. The toxic effect of the thymoxyacetic acid was similar to that of the commercial herbicide 2,4-D, that is, more pronounced in L. saliva (eudicot) than in S. bicolor (monocot).