Quaternary biopesticides and disinfectants derived from quinine and amino acids - environmental prospects and risks

The numerous risks associated with the toxicity of conventional quaternary ammonium salts (QASs) to various groups of living organisms have prompted the search for new, safer biologically active compounds synthesized in a sustainable manner from renewable raw materials. Here, we describe new QASs of natural origin containing quinine-based cation and anions derived from proteinogenic amino acids - l-asparagine and l-alanine. The quinine-derived QASs were thoroughly characterized in terms of correctness of chemical structure, physicochemical properties, and biological activity. It was discovered that due to quinine activity, the new salts exhibit strong antifeedant activity toward stored products pests, and in the case of elongation of the alkyl substituent in the 1-alkylquininium cation, they also become potent disinfectants. The performed analyses also allowed to assess the environmental risk by determining toxicity to monocotyledonous (Sorghum bicolor, Triticum aestivum) and dicotyledonous (Sinapis alba) terrestial plants, freshwater algae (Chlorella vulgaris) and crustaceans (Daphnia magna) at various concentrations of the test substance. None of the QASs of natural origin showed phytotoxicity, and salts containing short alkyl substituents in quinine-based cations were noticeably less toxic to aquatic organisms than the other tested compounds. The results indicate that although a trade-off between antimicrobial activity and aquatic toxicity must be made when designing new quinine-based antiseptics, it is possible to obtain potent, naturally-derived and relatively low-toxic biopesticides toward stored-product pests based on quinine and amino acids.