Naturally based ionic liquids with indole-3-acetate anions and cations derived from cinchona alkaloids.

Tomasz Kleiber,Tomasz Rzemieniecki,Juliusz Pernak

doi:10.1039/d1ra04805h

Tomasz Kleiber, Tomasz Rzemieniecki + Show 1 more

Open Access

https://doi.org/10.1039/d1ra04805h

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Abstract

The use of highly efficient methods and natural raw materials in syntheses of new biologically active substances addresses the current challenges in this area: ensuring the highest possible efficacy at low concentrations and reducing negative environmental impact. In the present study, we applied this strategy to obtain a new group of ionic liquids containing the indole-3-acetate anion, which is a well-known plant growth hormone, and a cation derived from a cinchona alkaloid – quinine or quinidine. A comparison of the derivatization kinetics of both alkaloids was also carried out, and the use of a quaternary quinidine derivative as a source of biologically active ionic liquids is described here for the first time. The structures of the obtained compounds were fully confirmed based on spectral methods. According to analyses of the effects of the obtained compounds on the growth and development of lettuce plants (Lactuca sativa L.), the ionic liquids obtained with indole-3-acetate anions exhibited activity at a concentration of 0.5 mg dm−3, and the length of the alkyl substituent in the alkaloid-derived cation or the chirality of this cation is crucial in determining the biological activity of the compound. In the cases of several salts containing the 1-alkylquininium cation, we recorded significant, beneficial changes in micronutrient content, which directly translated into plant nutritional value, while no signs of phytotoxicity were observed. Analyses of relevant physicochemical properties (e.g., with differential scanning calorimetry, thermogravimetric analysis and solubility analysis) as well as microbial toxicity tests were also performed to evaluate the environmental impacts of the products. The promising results of our study indicate significant potential for application of these new ionic liquids derived from cinchona alkaloids.

Highlights

According to analyses of the effects of the obtained compounds on the growth and development of lettuce plants (Lactuca sativa L.), the ionic liquids obtained with indole-3-acetate anions exhibited activity at a concentration of 0.5 mg dmÀ3, and the length of the alkyl substituent in the alkaloid-derived cation or the chirality of this cation is crucial in determining the biological activity of the compound
To obtain the designed ionic liquid (IL) based on cinchona alkaloids, it was necessary to synthesize quaternary derivatives of both quinine and quinidine in the rst step. 1-Alkylquininium bromides of high purity were obtained by the Menschutkin reaction using a homologous series of 1-bromoalkanes comprising 2 to 12 carbon atoms
The hydrogen atom H-2endo in the 1-ethylquinidinium cation is shielded compared to its counterpart in the quinine-based cation: its signal occurred at d 1⁄4 0.96 ppm, while the respective signal from the 1-ethylquininium cation was observed at 1.36 ppm

Summary

Introduction

One of the most important challenges in the sustainable development of modern biologically active chemicals is the design of novel ingredients characterized by unique modes of action.[1,2,3,4,5] It should be stressed that it is possible to obtain products with a very high level of biocompatibility when naturally derived compounds with strong biological effects on other living organisms are used as substrates.[6,7,8] Alkaloids are an interesting group of potential models for new biologically active compounds; this is a vast group of natural, organic substances with high structural diversity, whose common feature is the presence of a heterocyclic group containing a nitrogen atom with basic character.[9,10] Compounds in this group are characterized by the use of small doses with signi cant activity towards a broadThe strategy of using highly biologically active ingredients can be successfully applied in modern agrotechnology. Auxins are a attractive group of growth regulators, of which indole-3-acetic acid (IAA) is the best-known example Their high application potential is due to the fact that they exhibit biological activity at very low concentrations (as low as 10À12 mol dmÀ3)[14] and, at the same time, bene cially affect a number of important crop plant factors, including shoot growth,[15] rooting,[16,17] nutrient uptake and plant nutritive value,[18] as well as responses to stress factors.[19] The undoubted advantages of IAA include its biocompatibility and biodegradability[20,21] and the fact that it shows minor toxic effects for mammals (LD50 > 1000 mg kgÀ1; rat, oral).[22]

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