BACKGROUND: Pyrisoxazole is a fungicide that has two chiral carbon atoms and four isomers: (3S,5R)-, (3R,5S)-, (3S,5S)-, and (3R,5R)-pyrisoxazole. RESULTS: Pure crystals of four pyrisoxazole isomers were prepared by chiral separation and single-crystal cultivation. Their absolute configurations were established by X-ray single crystal diffraction analysis. Bioassays indicated that compound (3S,5R)-pyrisoxazole showed excellent fungicidal activity with a median effective concentration (EC 50) value of 0.14 ∼g mL −1 and protective activity with an EC 50 value of 13.29 ∼g mL −1. These values are superior to the commercial fungicides boscalid and racemic pyrisoxazole. CONCLUSIONS: The biological activity of racemic pyrisoxazole is due almost exclusively to the isomer (3S,5R)-pyrisoxazole; the other three isomers had very low activity.

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Diethyl 5-ethyl-2,3-pyridinedicarboxylate is an important organic intermediate and used in the field of dye, medicine and pesticide widely. Meanwhile, it also shows some biological activity. With the application of the efficient imidazolinone herbicides 1-9 which developed by American Cyanamid Company in the 1980's, the market demand risen dramatically 10. However, because of the backward domestic technology and equipment conditions, current process for diethyl 5-ethyl-2,3pyridinedicarboxylate comes with many disadvantages, such as high cost, low yield, serious pollution, etc., which significantly decrease the economic and social benefits. Therefore, a new efficient method for the preparation of diethyl 5-ethyl-2,3-pyridinedicarboxylate is desired 11-15. The general process of diethyl 5-ethyl-2,3-pyridinedicarboxylate is shown in Scheme-I. It takes diethyl oxalate and ethyl chloroacetate as raw materials, sodium ethoxide as catalyst to synthesize 2-chloro-3-oxo-succinic acid diethyl ester (M1) via Claisen condensation. Then in the presence of ammonium sulfamate, diethyl 5-ethyl-2,3-pyridinedicarboxylate is obtained by cyclizing M1 and 2-ethyl acrolein. However, there are a lot of problems about this process. Firstly, the current molar ratio of M1 and ammonium sulfamate is 1: 2.2. But the theoretical ratio is only 1:1, the excess nitrogen atom in the reaction flows into the waste water, which increases the difficulty of wastewater treatment. Secondly, the general method to deal with waste-water is evaporating concentration and burning organic substance in the waste water. Besides, burning the organic substances containing S atoms may give off sulfur dioxide

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