Browsing by Subject "Copper"

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Further limitations of synthetic fungicide use and expansion of organic agriculture in Europe will increase the environmental and health risks of chemical crop protection caused by copper‐containing fungicides
(2023) Burandt, Quentin C.; Deising, Holger B.; Tiedemann, Andreas von
Copper-containing fungicides have been used in agriculture since 1885. The divalent copper ion is a nonbiodegradable multisite inhibitor that has a strictly protective, nonsystemic effect on plants. Copper-containing plant protection products currently approved in Germany contain copper oxychloride, copper hydroxide, and tribasic copper sulfate. Copper is primarily used to control oomycete pathogens in grapevine, hop, potato, and fungal diseases in fruit production. In the environment, copper is highly persistent and toxic to nontarget organisms. The latter applies for terrestric and aquatic organisms such as earthworms, insects, birds, fish, Daphnia, and algae. Hence, copper fungicides are currently classified in the European Union as candidates for substitution. Pertinently, copper also exhibits significant mammalian toxicity (median lethal dose oral = 300–2500 mg/kg body wt in rats). To date, organic production still profoundly relies on the use of copper fungicides. Attempts to reduce doses of copper applications and the search for copper substitutes have not been successful. Copper compounds compared with modern synthetic fungicides with similar areas of use display significantly higher risks for honey bees (3- to 20-fold), beneficial insects (6- to 2000-fold), birds (2- to 13-fold), and mammals (up to 17-fold). These data contradict current views that crop protection in organic farming is associated with lower environmental or health risks. Further limitations in the range and use of modern single-site fungicides may force conventional production to fill the gaps with copper fungicides to counteract fungicide resistance. In contrast to the European Union Green Deal goals, the intended expansion of organic farming in Europe would further enhance the use of copper fungicides and hence increase the overall risks of chemical crop protection in Europe. Environ Toxicol Chem 2024;43:19–30. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.
Neuartige Kupfer-katalysierte und übergangsmetallfreie Methoden zum Aufbau von Heterocyclen
(2022) Rekowski, Szymon; Beifuss, Uwe
Heterocycles are the backbones of numerous drugs and are therefore of great importance in medicinal chemistry. As a result, there is an inevitably high demand for methods to synthesize heterocycles. The requirements for new methods for the synthesis of heterocycles are nowadays very high, as they must not only be efficient and selective, but also sustainable. These prerequisites can be met by both transition metal-free and transition metal-catalyzed reactions. Thus, the transition metal-free preparation of a variety of different heterocycles can be achieved by radical, cationic and anionic cyclizations as well as by pericyclic reactions. Recently, the importance of electrochemical and photochemical methods in heterocyclic synthesis has been increasing very rapidly. In transition metal-catalyzed heterocycle synthesis, Pd- and Cu-catalysts in particular play a prominent role. For the Pd-catalyzed assembly of N-heterocycles, the intramolecular Buchwald-Hartwig amination is especially noteworthy. It is now known that many Pd-catalyzed reactions can also be carried out with Cu-catalysts. In view of the fact that Cu-catalysts are much cheaper due to the higher abundance of Cu, and that expensive ligands can usually be omitted to carry out Cu-catalyzed reactions, their enormous importance in heterocyclic synthesis is easy to understand. For example, many N-heterocycles can be prepared by intramolecular Ullmann reactions with excellent yields and high selectivities. Here, bisfunctionalized substrates with two centers of different reactivity play a major role. The aim of the present work was to develop new efficient and highly selective synthetic methods for the construction of relevant N- or O-heterocycles. In particular, Cu-catalyzed reactions with bisfunctionalized substrates were to be developed. The investigation included determining whether the corresponding reactions can also be carried out in the absence of transition metal catalysts. Benzodioxines and 2,3-dihydrobenzodioxines exhibit many interesting biological properties, but the possibilities available nowadays for their synthesis are limited. Therefore, the first part of this dissertation deals with the development of a new method for the diastereospecific construction of (Z)-2-arylidene-2,3-dihydrobenzodioxines (Z)-80 (Scheme 50) by reacting 3-aryl-substituted (Z)-1,2-dibromoarylpropenes (Z)-82 with catechols 83. While the model substrate (Z)-82a (R1 = Ph) can be prepared by reduction and subsequent bromination of a-bromocinnamaldehyde, the remaining substrates (Z)-82 were prepared in three steps from the corresponding benzaldehydes. Subsequent optimization of the model reaction under a wide variety of reaction conditions showed that the best results could be obtained under transition metal-free conditions. The highest yield of (Z)-80a was obtained when 1 equivalent of (Z)-82a (R1 = Ph, R2 = H) was reacted with two equivalents of 83a (R2 = H) in the presence of four equivalents of Cs2CO3 in DMF for 18 h at 140 °C. Remarkably, this transition metal-free domino reaction, which consists of an intermolecular O-allylation followed by an intramolecular O-vinylation, is highly diastereospecific: the use of (Z)-1,2-dibromo-3-phenyl-2-propene [(Z)-82a] exclusively delivers (Z)-2-benzylidene-2,3-dihydrobenzodioxines [(Z)-80a]. This high diastereospecifity was also observed in the reactions of all other substrates (Z)-82. The 2-arylidene-2,3-dihydrobenzodioxins (Z)-80 were obtained in yields up to 89%. This method tolerates different substituents on the aromatic moiety of (Z)-82 as well as different disubstituted catechols 83. DFT calculations conducted in collaboration with Prof. Bharatham, NIPER Nagar (Mohali), suggest that the intramolecular O-vinylation proceeds via an alkene intermediate rather than an alkyne intermediate. The diastereoselective conversion of the E-configured substrate (E)-82a (R1 = Ph) to the corresponding (E)-2-benzylidene-2,3-dihydrobenzodioxine [(E)-80a] supports this assumption. The second part of this work is devoted to the intramolecular Cu(I)-catalyzed cyclization of o-haloarylideneguanylhydrazone salts (E)-86 for the direct construction of N-1 unsubstituted 1H-indazoles 84 (Scheme 51). The synthesis of indazoles of this type is of particular interest to medicinal chemistry because they form the backbone of some important anticancer drugs. Substrates (E)-86 were prepared by condensation of o-halobenzaldehydes with aminoguanidine hydrochloride in yields up to 90%. Subsequent cyclization using 10 mol% CuI, 30 mol% DMEDA and 0.5 equivalents of Cs2CO3 afforded the 1H-indazoles 84 in yields up to 75%. The reactions were carried out at 120 °C in DMF for 5 h in a sealed glass tube. The method tolerated a full range of substituents on the aromatic moiety of the substrates. Based on DFT calculations done in collaboration with Prof. Bharatham, NIPER Nagar (Mohali), it is reasonable to assume that E/Z isomerization of substrate 86 occurs first, followed by metal complexation with subsequent C,N bond formation. The final hydrolysis of the 1H-indazole-1-carboximidamide yields the N-1 unsubstituted 1H-indazole 84.
The importance of soil microorganisms and cover crops for copper remediation in vineyards
(2014) Mackie, Kathleen; Kandeler, Ellen
The historical use of copper fungicides, as a plant protection agent, has moderately polluted agricultural topsoils across Europe. Organic agriculture, in particular, continues to be limited to the use of copper fungicides due to a lack of permitted alternative plant protection agents. In recent years, the effects of copper accumulation in the soil have been observed. Studies on the negative effects of copper in agricultural soils show a decrease in ecosystem services, which rely on macro- and micro-organisms. Thus, there is the question of how to remediate copper polluted crop fields. Although this topic has more recently been investigated in the laboratory, currently, there are no experiments available in the field. Viticulture is one of the largest perennial crops in Europe that utilize copper fungicides. Therefore, this dissertation was designed to investigate copper remediation strategies in vineyards, in order to best understand potential solutions for a growing problem, as well as their effect on ecosystem services. Understanding the reaction of and support by soil microorganisms will help determine which strategy has the best potential. The main project was implemented using two field experiments, each of which analyzed copper availability, microbial abundance, function and community composition to determine the overall outcome of copper remediation. The dissertation is presented in four papers. The first paper is a review on copper in vineyards, which focused specifically on cutting-edge remediation strategies currently being studied. This paper also provided information on knowledge gaps in the literature. The second paper showed the spatial distribution of copper and soil microorganisms at the plot scale, providing a better understanding of copper and microbial distribution as well as a foundation for subsequent papers. The third paper analyzed copper phytoextraction by single species and mixed species cover crop plots and the microbial community that may support it. The fourth paper was aimed at observing the ability of biochar and biochar-compost to immobilize copper and improve ecosystem services. The studies utilized classic soil biological methods (enzyme activities, microbial C and N, ergosterol) and modern molecular techniques (quantitative polymerase chain reaction (qPCR) of 16S rRNA and taxa specific bacteria genes and phospholipid fatty acid analysis (PLFA)) as well as determination of chemical soil properties and copper fractions.