Abstract
Series of seventeen new multihalogenated 1-hydroxynaphthalene-2-carboxanilides was prepared and characterized. All the compounds were tested for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. 1-Hydroxy-N-phenylnaphthalene-2-carboxamides substituted in the anilide part by 3,5-dichloro-, 4-bromo-3-chloro-, 2,5-dibromo- and 3,4,5-trichloro atoms were the most potent PET inhibitors (IC50 = 5.2, 6.7, 7.6 and 8.0 µM, respectively). The inhibitory activity of these compounds depends on the position and the type of halogen substituents, i.e., on lipophilicity and electronic properties of individual substituents of the anilide part of the molecule. Interactions of the studied compounds with chlorophyll a and aromatic amino acids present in pigment-protein complexes mainly in PS II were documented by fluorescence spectroscopy. The section between P680 and plastoquinone QB in the PET chain occurring on the acceptor side of PS II can be suggested as the site of action of the compounds. The structure-activity relationships are discussed.
Highlights
In spite of the fact that various classes of herbicides are known and currently can be classified according to about 20 different modes of action [1], over 50% of marketed herbicides act by reversible binding to photosystem II (PS II) [2]
Many herbicides acting as photosynthetic electron transport (PET) inhibitors in PS II containing an amide and/or a carbamate moiety, which is able to form hydrogen bonds between the CONH/NHCOO group of amides/carbamates and the target proteins in photosynthetic centres of thylakoid membranes resulting in changes in protein conformation and in PET inhibition, have been shown to be the most potent type of this class of herbicides [11,12,13]
It could be suggested that the site of inhibitory action of the halogenated 1-hydroxynaphthalene-2-carboxanilides is situated on the acceptor side of PS II, at the section between P680 and QB
Summary
In spite of the fact that various classes of herbicides are known and currently can be classified according to about 20 different modes of action [1], over 50% of marketed herbicides act by reversible binding to photosystem II (PS II) [2] This effect results in the interruption of the photosynthetic electron transport (PET) [3,4,5]. Many herbicides acting as PET inhibitors in PS II containing an amide and/or a carbamate moiety, which is able to form hydrogen bonds between the CONH/NHCOO group of amides/carbamates and the target proteins in photosynthetic centres of thylakoid membranes resulting in changes in protein conformation and in PET inhibition, have been shown to be the most potent type of this class of herbicides [11,12,13] Both moieties can be substituted, and their properties can be modified [14,15]. The results were completed by seven recently published unsubstituted and monochlorinated and brominated derivatives [11], and the structure–activity relationships (SAR) of all the mentioned compounds are discussed
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