A series of twelve 2-[(E)-2-substituted-ethenyl]-1,3-benzoxazoles was designed. All the synthesized compounds were tested against three mycobacterial strains. The compounds were also evaluated for their ability to inhibit photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. 2-[(E)-2-(4-Methoxyphenyl)ethenyl]-1,3-benzoxazole, 2-[(E)-2-(2,3-dihydro-1-benzofuran-5-yl)ethenyl]-1,3-benzoxazole and 2-{(E)-2-[4-(methylsulfanyl)phenyl]ethenyl}-1,3-benzoxazole showed the highest activity against M. tuberculosis, M. kansasii, and M. avium, and they demonstrated significantly higher activity against M. avium and M. kansasii than isoniazid. The PET-inhibiting activity of the most active ortho-substituted compound 2-[(E)-2-(2-methoxyphenyl)ethenyl]-1,3-benzoxazole was IC₅₀ = 76.3 μmol/L, while the PET-inhibiting activity of para-substituted compounds was significantly lower. The site of inhibitory action of tested compounds is situated on the donor side of photosystem II. The structure-activity relationships are discussed.

Department of Chemical Drugs Faculty of Pharmacy University of Veterinary and Pharmaceutical Sciences Brno Palackeho 1 3 612 42 Brno Czech Republic

Department of Environmental Ecology Faculty of Natural Sciences Comenius University Mlynska dolina Ch 2 842 15 Bratislava Slovakia

Department of Inorganic and Organic Chemistry Faculty of Pharmacy in Hradec Kralove Charles University Prague Heyrovskeho 1203 500 05 Hradec Kralove Czech Republic

Institute of Chemistry Faculty of Natural Sciences Comenius University Mlynska dolina Ch 2 842 15 Bratislava Slovakia

Institute of Organic Chemistry and Technology Faculty of Chemical Technology University of Pardubice Studentska 573 532 10 Pardubice Czech Republic

Institute of Organic Chemistry and Technology Faculty of Chemical Technology University of Pardubice Studentska 573 532 10 Pardubice Czech Republic ; Department of Inorganic and Organic Chemistry Faculty of Pharmacy in Hradec Kralove Charles University Prague Heyrovskeho 1203 500 05 Hradec Kralove Czech Republic

Laboratory for Mycobacterial Diagnostics and TB Institute of Public Health in Ostrava Partyzanske namesti 7 702 00 Ostrava Czech Republic

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