Absolute configuration of four chiral isomers of pyrisoxazole and their bioactivity.

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 ) value of 0.14 μg mL and protective activity with an EC value of 13.29 μg mL . 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. © 2020 Society of Chemical Industry.