5-Aryl-1,3,4-oxadiazole-2-thiols as a New Series of trans-Cinnamate 4-Hydroxylase Inhibitors

Abstract

A series of 5-aryl-1,3,4-oxadiazole-2-thiols was found to inhibit trans-cinnamate 4-hydroxylase (C4H) from Populus kitakamiensis, which was expressed in yeast. 5-Phenyl-1,3,4-oxadiazole-2-thiol showed inhibitory activity comparable to 2-hydroxy-1-naphthoic acid, a known C4H inhibitor. Studies on the structure-activity relationship indicated that the presence of a thiol group was significant for stronger activity. Of the compounds tested, 5-(3-fluorophenyl)-1,3,4-oxadiazole-2-thiol was the most active. AE Pesticide Science Society of Japan Keywords: trans-cinnamate 4-hydroxylase, 5-aryl-1,3,4-oxadiazole-2-thiols, cytochrome P450, Populus kitakamiensis. INTRODUCTIONThe trans-cinnamate 4-hydroxylase (C4H) is a cytochrome P450 which catalyzes the hydroxylation of trans-cinnamic acid into pcoumaric acid, the first oxygenation step in the metabolism of phenylpropanoids in plants.1) Phenylpropanoid metabolism is a plant-specific pathway leading to a variety of compounds such as lignins, lignans, flavonoids, isoflavonoids and coumarins, which are essential for plant development and defense against ultraviolet light, predators and pathogens. C4H, which is highly inducible by wounding and pathogen infection, is indicated to be the major enzyme in the regulation of lignification and defenserelated reactions.2) Therefore, specific C4H inhibitors would offer an attractive means of studying the important phenylpropanoid pathway of plants. Since C4H has not been found in any invertebrate or vertebrate animals, it might be an unexploited target for development of a new herbicide. Schalk et al. described 2-hydroxy-1-naphthoic acid (1) 3) and piperonylic acid (2) 4) as a competitive inhibitor and a mechanism-based inactivator of C4H, respectively. There is no report in the literature of C4H inhibitors other than these structural analogs of cinnamic acid. By random screening, we have recently found that 5-phenyl-1,3,4-oxadiazole-2-thiol strongly inhibits C4H, CYP73a from Populus kitakamiensis, which is expressed in yeast. In the present paper we report the structure-activity relationships of a series of 5-aryl-1,3,4-oxadiazole-2-thiols. MATERIALS AND METHODS Chemicals2-Hydroxy-1-naphthoic acid and piperonylic acid were purchased from Tokyo Kasei Co. Compound 3 was purchased from Aldrich Co. 2-Methylthio-5-phenyl-1,3,4-oxadiazole (4) was prepared by methylation of 3 with methyl iodide.5) 2-Phenyl-1,3,4-oxadiazole (5) was prepared according to the reported method. 6) 5-Substituted-1,3,4-oxadiazole-2-thiols (7-30) were synthesized from the reaction of the corresponding hydrazides and carbon disulfide in the presence of potassium hydroxide according to procedures reported previously. [6][7][8] The structures of the compounds were confirmed using 1 H-NMR spectra which were recorded on a JEOL EX-400 (400 MHz) spectrometer. The following procedure for the preparation of 5-(3-fluorophenyl)-1,3,4-oxadiazole-2-thiol (23) is typical. To a solution of 2.6 g of 3-fluorobenzohydrazide and 1.2 g of potassium hydroxide in 20 ml of ethanol was add...

Synthesis and herbicidal activity of novel 5-chloro-3-fluoro-2-phenoxypyridines with a 1,3,4-oxadiazole ring

“…Then, the ring closer reaction of compound (2) with carbon disulfide under basic conditions and subsequent acidification yielded the intermediate (3). Subsequent S-substitution on the 1,3,4-oxadiazole ring gave the final products (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Chemical structures of the compounds synthesized were confirmed by 1 H-NMR spectra, IR and elemental analysis data, which are shown below.…”

“…The ring closure reaction of 2 with carbon disulfide under basic conditions and subsequent acidification yielded intermediate 3. Various reagents, such as alkyl bromide or acyl halide, were then reacted with compound 3 in the presence of potassium hydroxide in order to introduce a substituent onto the sulfur atom at the 5-position of the 1,3,4-oxadiazole ring, so that novel 13 kinds of compounds (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) were provided in moderate to high yield ( Table 1). The results of spectroscopic data, 1 H NMR and 13 C NMR, IR spectra and elemental analysis are presented in the experimental section.…”

“…[8][9][10][11][12] Furthermore, 1,3,4-oxadiazoles [13][14][15][16] and thiadiazole [17][18][19][20] are known as having a broad spectrum of potential herbicidal activities. Due to the biological importance of 1, 3, 4-oxadiazoles, which are derived from ester moiety, it was considered of interest to link them to the clodinafop herbicide framework.…”

Synthesis and Evaluation of Anticancer Activity of 1, 3, 4-Oxadiazole Derivatives against Ehrlich Ascites Carcinoma Bearing Mice and Their Correlation with Histopathology of Liver

“…2 Therefore, identification of novel potent, less toxic and selective mechanism of action anticancer agents remains one of the most imperative health problems. 3 1,3,4-Oxadiazoles are an important class of heterocyclic compounds 4 with a broad range of biological activities such as anti-inflamma- 23-11-2016 tory, analgesic and ulcerogenicity, 5 apoptosisinducer, 6 antimycobacterial, 7 antifungal, 8 antitumor, 3,6,9 P-Glycoprotein Inhibitors, 10 pesticides and insecticides, 11 4-Hydroxylase Inhibitors, 12 anticonvulsant activity 13 etc.…”

Inhibition of trans-Cinnamate 4-Hydroxylase by 4-Amino-5-aryl-2,3-dihydro-3H-1,2,4-triazole-3-thiones

“…We have previously reported that a series of 5-aryl-1,3,4-oxadiazole-2-thiols inhibited C4H from Populus kitakamiensis, which was expressed in yeast. 3) We further examined several heterocycles, and found that 4-amino-5-phenyl-2,4-dihydro-3H-1,2,4-triazole-3-thione (1) showed strong inhibitory activity against C4H expressed in yeast. Although some 5-aryl-2,4-dialkyl-2,4-dihydro-3H-1,2,4-triazole-3-thiones have been reported to show antidepressant activity, 4) there has been no report on the inhibitory activity of 1 toward C4H.…”