OAT PHENOLICS - AVENALUMIC ACIDS, A NEW GROUP OF BOUND PHENOLIC-ACIDS FROM OAT GROATS AND HULLS

A new group of phenolic acids was found in aqueous alcoholic extracts of both oat groats and hulls. These acids occurred as conjugates covalently linked to the amine function of several different orthoaminobenzoic acids. One of the conjugates was a pale yellow crystalline solid with a molecular weight of 325 (C18H15NO5). Mass spectral studies revealed an acid composed of C11H10O3 and a molecular weight of 190. Structural analysis (H-1-, C-13-nuclear magnetic resonance, ultraviolet, etc.) allowed formulation of the acid as 5-(4'-hydroxyphenyl)-penta-2,4-dienoic acid (i.e., 4'-hydroxycinnamylidene-acetic acid), for which the trivial name avenalumic acid is proposed. Comparison of proton coupling constants of the naturally occurring conjugate with models suggests that the oat constituent is an interconvertible mixture of the 2-E,4-E and 2-Z,4-E isomers, with the former isomer predominating. This assignment was confirmed by total synthesis of 2-E,4-E-avenalumic acid. Two additional derivatives of avenalumic acid were also detected: the 3'-hydroxy- and 3'-methoxy analogues. These acids, which are the ethylenic homologues of the well-known p-coumaric, ferulic, and caffeic acids, may be widely distributed in cereal grains.