Avenalumins I, II and III were isolated as phytoalexins from oat leaves infected with the crown rust fungi, Pccinia coronata f. sp. avenae. Avenalumins I, II and III were characterized as 2-[2-(4-hydroxyphenyl)ethenyl]-6-hydroxy-4H-3,1-benzoxazin-4-one [VII], 2-[2-(3-methoxy-4-hydroxyphenyl)ethenyl]-6-hydroxy-4H-3,1-benzoxazin-4-one [VIII] and 2-[2-(4-hydroxyphenyl)butadienyl]-6-hydroxy-4H-3,1-benzoxazin-4-one [IX], respectively. These structures were confirmed by total syntheses. Phytopathological experiments suggested that avenalumins play important roles on the resistance of oat to the crown rust disease.
