Study On Chiral Isomers And Biological Activity Of Pyrisoxazole

Pyrisoxazole is a new agricultural fungicide invented by Shenyang Research Institute of Chemical Industry.It has become an agricultural fungicide,with unique mechanism of fungicidal activities,outstanding control effect and the best market performance in controlling diseases such as gray mold of crops.Pyrisoxazole is a typical chiral compound with two chiral carbon atoms in its structure,two geometric isomers and four chiral isomers.Pyrisoxazole is a relatively new member of isoxazolidine fungicide.Up to now,the study of reaction risk,apparent thermodynamics and kinetics,isomer resolution,absolute configuration preparation and characterization,and the study of biological activity of each isomer are the key points in the research of pyrisoxazole,and it is also an urgent problem to be solved in the industrialization of pyrisoxazole.In this paper,the reaction mechanism of pyrisoxazole synthesis was studied,the chemical reaction hazards of pyrisoxazole synthesis was studied.The analytical methods of four chiral isomers of pyrisoxazole was studied.Single crystals of four chiral isomers were prepared and characterized by SXRD and Circular spectrum,etc.The absolute configurations of four chiral isomers were determined.The biological activity of four chiral isomers was studied,then the relationship between biological activity and absolute configuration was discussed.A new method for the one-step synthesis of pyrisoxazole was studied,with the 3-acetyl pyridine,N-methylhydroxylamine sulfate and p-chloroprene as the raw materials,and sodium acetate as the buffer.The optimum technological conditions such as solvent and dosage,temperature of N-methoxyhydroxylamine sulfate feeding and reaction time were determined,and the yield of pyrisoxazole reached 72.8%.On-line infrared spectroscopy combined with liquid chromatography was used to study the one-step synthesis mechanism of pyrisoxazole.The reaction was the synergistic effect of 1,3-dipolar cycloaddition.The formation rate of intermediate-nitrone was controlled by the feeding rate of N-methylhydroxylamine sulfate,while the overall reaction rate was controlled by 1,3-dipolar cyclization.The chemical reaction hazards study of one-step synthesis of pyrisoxazole was carried out,and the apparent thermodynamic and kinetic data of the main reaction substances and reaction process in the target process were obtained.The apparent heat of reaction of pyrisoxazole in one-step method is-1298.7 k J kg^-1（calculated by the weight of 3-acetylpyridine）,the adiabatic temperature riseΔT of the runaway system is 59.4 K,the highest temperature MTSR that the system can reach is 135.9℃,and the time to maximum rate is 24 hours corresponding the temperature of 116.8℃,that means TD₂₄=116.8℃when the reaction is out of control.The analysis and separation methods of four chiral isomers of pyrisoxazole were studied.Reversed-phase high performance liquid chromatography and chiral column were used for analysis and separation.The effects of mobile phase composition and ratio on analysis and separation were studied,and the favorable conditions were determined.The chromatographic separation degree of each chiral isomer of pyrisoxazole was above 1.5.Four chiral isomers of pyrisoxazole（3S,5R）-PZ,（3R,5S）-PZ,（3R,5R）-PZ and（3S,5S）-PZ were obtained,and the purity of four chiral isomers was all above 98.0%.The single crystals of four chiral isomers of pyrisoxazole were prepared by liquid phase diffusion combined with solvent evaporation,with dichloromethane and petroleum ether as a mixed solvent.The absolute configurations of four chiral isomers were determined by SXRD,Circular spectrum,1H-NMR,DSC,FT-IR,etc.And made a standard chemical name for the our chiral isomers.（3S,5R）-PZ is（3S,5R）-5-（4-chlorophenyl）-2,3-dimethyl-3-（pyridine-3-yl）isoxazoline,（3R,5S）-PZ is（3R,5S）-5-（4-chlorophenyl）-2,3-dimethyl-3-（pyridine-3-yl）isoxazoline,they are are enantiomers,with the cis（Z-body）geometric configuration.（3R,5R）-PZ is（3R,5R）-5-（4-chlorophenyl）-2,3-dimethyl-3-（pyridine-3-yl）isoxazoline,（3S,5S）-PZ is（3S,5S）-5-（4-chlorophenyl）-2,3-dimethyl-3-（pyridine-3-yl）isoxazoline,they are enantiomers,with the trans（E-body）geometric configuration.It was found that（3S,5R）-PZ was the highest biological activity compound,after the test of inhibition of mycelial growth and conidial germination of Botrytis cinerea Pers,sclerotinia sclerotiorum de Bary and Monilinia ariae Whetz,the one day protective activity against botrytis cinerea,the one day therapeutic activity against botrytis cinerea,and the internal absorption activity against botrytis cinerea.The bactericidal activity,therapeutic activity,systemic activity and protective activity of（3S,5R）-PZ are all obviously better than（3R,5S）-PZ,（3R,5R）-PZ and（3S,5S）-PZ,and also better than pyrisoxazole racemate and the boscalid from BASF.The relationship between biological activity and the absolute configuration of（3S,5R）-PZ was discussed.It was speculated that the oxygen atom in the structure of pyrisoxazole was the key factor leading to the bactericidal activity of isoxazoline compounds.When the oxygen atom in the isoxazoline ring obtained a more prominent spatial structure,it showed better biological activity.It is suggested that the C₃-O₁-N₁bond angle affects the spatial structure of oxygen atoms in piconazole.The C₃-O₁-N₁bond angle of（3S,5R）-PZ is the smallest,and the area of oxygen atoms contacting and being exposed to the surrounding environment is the largest,so it is easier to interact with biological targets and has higher biological activity.This research has applied for Chinese invention patent and PCT patent.