New Dimeric Compounds of Avenanthramide Phytoalexin in Oats

Avenanthramide B is an oat phytoalexin produced in response to pathogen attack and elicitation. We found the formation of new dimers (1-5) of avenanthramide B in elicited oat leaves. The dimers were synthesized by a reaction of peroxidase and avenanthramide B in the presence of hydrogen peroxide. The structures of 1-5 were determined by spectroscopic analyses, chemical derivatization, and 15N labeling. Compound 1 was a dehydrodimer of avenanthramide B with a bisbutane lactam skeleton, while 2-4 were monohydrated dehydrodimers with butane lactam structures. Compound 5 was also a monohydrated dehydrodimer but with a tetrahydrofuran structure. All the compounds were classified into lignanamides that were formed by an 8'-8' coupling reaction between two avenanthramide B units.