DIBENZOFURAN PHYTOALEXINS FROM THE SAPWOOD OF COTONEASTER-ACUTIFOLIUS AND 5 RELATED SPECIES

Five dibenzofuran phytoalexins were isolated and characterized by NMR techniques from the fungal-inoculated sapwood tissue of Cotoneaster acutifolius. One is the known cotonefuran, here renamed alpha-cotonefuran. The other four an new dibenzofurans: beta-cotonefuran (7-hydroxy-2,3,4,6-tetramethoxy), gamma-cotonefuran (2,7-dihydroxy-3,4-dimethoxy), delta-cotonefuran (2-hydroxy-3,4,7-trimethoxy) and epsilon-cotonefuran (2,6-dihydroxy-3,4,7-trimethoxy). One or more of these cotonefurans were detected as phytoalexins in sapwoods of four other Cotoneaster species and Mespilus germanica. Their activities were measured against pathogenic and non-pathogenic fungi, and they gave ED(50) values in the range of 14-90 ppm. They proved to be fungistatic on spore germination rather than fungitoxic.