Transformation of herbicides into dual function quaternary tropinium salts

Abstract

Tropine was proposed as a cheap and sustainable source of plant growth regulating cation (N-alkyltropinium) and paired with herbicidal anions (3,6-dichloro-2-metoxybenzoate or 4-chloro-2-methylphenoxyacetate). The synthesised salts were obtained with 82–99% yield and exhibited high water solubility and surface-active properties, without excessive foam formation. Further experiments revealed plant growth promoting properties towards maize with simultaneous enhanced herbicidal action towards cornflower. At the same time, the obtained formulations exhibited high antimicrobial activity towards common soil bacteria Pseudomonas putida and Bacillus cereus (MIC 0.003–1.0 mmol L⁻¹). Moreover, it was confirmed that the synthesised salts were not biodegradable due to low susceptibility of cations for biotransformation. Overall, the results suggest that quaternary tropinium salts exhibit promising plant growth promoting properties as well as inhibition of weed development.