A series of benzopyrano[2,3-c]pyrazol-4(2H)-one derivatives were synthesized from readily available 1-phenyl- and 1-methyl-1H-pyrazol-3-ols by sequentially employing O-acylation, Fries rearrangement and potassium carbonate-induced cyclization. The anthelmintic properties of the obtained compounds were investigated in vivo in a model nematode, Caenorhabditis elegans. Five compounds, namely 2-phenyl[1]benzopyrano[2,3-c]pyrazol-4(2H)-one 33 and its 7-fluoro, 7-chloro-, 7-bromo- and 8-fluoro-analogues, 36, 38, 40 and 43, respectively, altered the development of C. elegans. While the activities of 33 and 43 were rather modest, compounds 36, 38 and 40 inhibited the growth of the worms at concentrations of approximately 1-3 µM. At these concentrations, the compounds did not kill the worms, but they strongly inhibited their development, with the majority of larvae never progressing past the L1 stage. Moreover, testing in non-cancer human cell lines showed that, with exception of 7-bromo derivative 40, the active compounds have favourable toxicity profiles.

Department of Chemical Biology and Genetics Faculty of Science Centre of the Region Haná for Biotechnological and Agricultural Research Palacký University Šlechtitelů 27 78371 Olomouc Czech Republic

Department of Organic Chemistry Kaunas University of Technology Radvilėnų pl 19 50254 Kaunas Lithuania

Division of Drug Synthesis Department of Pharmaceutical Chemistry University of Vienna Althanstrasse 14 1090 Vienna Austria

Institute of Synthetic Chemistry Kaunas University of Technology K Baršausko g 59 51423 Kaunas Lithuania

Laboratory of Growth Regulators Institute of Experimental Botany The Czech Academy of Science Palacký University Šlechtitelů 27 78371 Olomouc Czech Republic

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