Abstract: Numerous similarities exist between the structure–activity relationships of pharmaceutical drugs and pesticides, creating the potential for finding new crop management tools with novel mechanisms of action. Analogues of pyrazinamide and its active metabolite pyrazinoic acid were evaluated on a variety of monocot and dicot species to assess their potential as commercial herbicides. Six analogues, applied postemergence at 3 kg ai/ha, controlled yellow nutsedge (Cyperus esculentus) ≥ the commercial standards bentazon or imazethapyr. The compound 5-fluoropyrazine-2-carboxylic acid provided between 71 and 95% control of barnyardgrass (Echinochloa crus-galli) and yellow nutsedge with only modest injury (8–25%) to soybean (Glycine max). A similar compound containing a bromine atom in the 5-position controlled yellow nutsedge greater than bentazon and affected soybean, sweet corn (Zea mays convar. saccharata var. rugosa), and rice (Oryza sativa) in a similar fashion to bentazon as well. The herbicidal sites of action targeted by these analogues of pyrazinamide and pyrazinoic acid are unknown, but it is hypothesized that they may be disrupting targets in the biosynthesis pathways of nicotinamide adenine dinucleotide (NAD) and/or ethylene.
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A solution of 6-chloro-pyridazine-3-carboxylic acid (700 mg, 4.53mmol) in thionyl chloride (15 ml) was refluxed for 3 h. The reaction was cooled to ambient temperature and evaporated to dryness. Sodium methoxide (244 mg, 4.53 mmol) in [MEOH] (20 ml) was added to the residue and the solution was stirred on at room temperature (rt). [H2O] was added and the mixture was extracted three times with DCM. The combined organic phases were dried and concentrated. Flashchromatography [(SI02,] Heptane/EtOAc 1: 1) afforded 560 mg (72percent) of the title compound. [1H] NMR [(CDC13),] 5 (ppm): 4.09 (s, 3 H), 7.69 (d, 1 H), 8. 18 (d, 1 H). [LC-MS] [(M++1)] : 173 and 175 (3: 1).
Step 1: To a mixture of compound 7-1 (4.14 g, 26.1 mmol) in DCM (100 mL) was added oxalyl chloride (3.98 g, 31.3 mmol) dropwise. DMF (0.05 mL) was added and the resulting mixture was stirred at room temperature until the compound 7-1 was dissolved. Then MeOH (2 mL) was added dropwise and stirred for another 0.5 hr. After being washed with brine (100 mL), the mixture was dried over anhydrous Na2SC>4 and concentrated to give crude product. The crude product was purified by silica-gel column chromatography (eluting with PE/EA = 4/1) to yield the desired product 7-2 as white solid. LC-MS: m/z = 173.1
With dmap; In tetrahydrofuran; at 50.0℃; for 1.0h;
A suspension of (1) (2.0g, 12.7mmol) and 4-(dimethylamino)pyridine (776mg, 6.3mmol) in THF (50ml_) was treated with di-fe/f-butyl dicarbonate (3.6g, 16.5mmol). It was heated up to 50C for 1 h, then stirred at rt overnight. The reaction mixture was concentrated in vacuo, re-dissolved in EtOAc (20ml_), poured into HCI solution (1 M, 20ml_) and extracted with EtOAc (2 x 20ml_). The combined organics were washed with NaHC03 solution (50ml_) and brine (50ml_), dried over MgS04, filtered and concentrated in vacuo. Purification by silica gel column chromatography with hexane/EtOAc (1 :0-3: 1 ) yielded (2) as a white solid (2.2g, 81 %). (0878) LCMS (ES): Found 237.0 [M+Naf. (0879) 1H NMR (300 MHz, Chloroform-cf), d: 8.08 (d, J= 8.7 Hz, 1 H), 7.63 (d, J=8.9 Hz, 1 H), 1.67 (s, 9H).
56%
With dmap; In dichloromethane; at 20.0℃; for 12.0h;
Dissolve 6-chloropyridazine-3-carboxylic acid (7a) (2g, 12.62mmol) in 20mL DCM, add DMAP (3.08g, 25.23mmol),(Boc)2O (5.51g, 25.23mmol) was added at room temperature, and the reaction was stirred at room temperature for 12h.The solvent was removed under reduced pressure, and the residue was separated and purified by silica gel column chromatography (ethyl acetate/petroleum ether (v/v)=10/1-3/1),The tert-butyl 6-chloropyridazine-3-carboxylate (7b) (1.5 g, yield: 56%) was obtained.
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