The phytotoxin diplopyrone is considered to be the main phytotoxin of the fungus that is responsible for cork oak decline. Our laboratory developed a stereoselective synthesis of the enantiomer of the structure originally proposed for diplopyrone and we have synthesized other new pyranopyrans in conjunction with their evaluation as antibacterials or herbicides. Structural analogs based on the pyranopyran core were synthesized using carbohydrate starting materials in two complementary approaches that involve the chemistry of C-glycosides. Enantioselective synthesis of non-carbohydrates from carbohydrate starting materials was a well-known strategy for the synthesis of natural products in the Fraser-Reid laboratory. Biological assays of compounds in this study revealed potent antibacterial activity for a nitrile analog against common bacterial pathogens E. ictaluri and F. columnare that cause enteric septicemia (ESC) and columnaris disease, respectively, in catfish. Bioassay of the nitrile against E. ictaluri indicated approximately 100 times greater potency than the antibiotic florfenicol used commercially for this disease. Phytotoxic activity of target compounds was also observed. The antibiotic and phytotoxic activities of the new pyranopyrans synthesized in this study demonstrate the potential of such compounds as antibiotics and herbicides.

Synthesis and biological evaluation of antibacterial pyranopyrans

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ACS Fall 2022

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