Structures of the four avenacins, oat root resistance factors to ‘take-all’ disease

Abstract

The true aglycones of the avenacins are acid sensitive triterpene 12,13-epoxides, not 12-ketones, and one such avenestergenin epoxide is isolated direct from oat roots; this, together with study of the attached trisaccharide, permits complete structures to be proposed for the four avenacins (3a—d); avenestergenins readily undergo an acid-catalysed anhydrodimerisation via acetal formation.