IDENTIFICATION AND SYNTHESIS OF NEW FERULIC ACID DEHYDRODIMERS PRESENT IN GRASS CELL-WALLS

Seven isomeric dehydrodimers of ferulic acid (4-hydroxy-3-methoxycinna mic acid) have been synthesized and identified in extracts of saponifi ed cell walls of cocksfoot, switchgrass, and suspension-cultured corn. Dehydrodimers E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid , enyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid, yl]-2-metho xyphenoxy}-4-hydroxy-3-methoxy-cinnamic acid, nyl]-2-methoxyphenoxy}-4 -hydroxy-5-methoxycinnamic acid. )-4,4'-dihydroxy-3,5'-dimethoxy-beta, 3'-bicinnamic acid, ,4'-dihydroxy-3,3'-dimethoxy-beta,beta'-bicinnamic acid, and 6-methoxy-1,2-dihydro-naphthalene-2,3-dicarboxylic acid, al l arise from oxidative coupling of ferulate esters in cell walls and r epresent products of 8-5, 8-8, 8-O-4, 4-O-5, and 5-5 radical coupling. Prior literature has acknowledged only the presence of the 5-5-couple d dehydrodimer E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid . Consequently, by measuring only a single dehydrodimer and assuming i nappropriate response factors, ferulate dehydrodimers have been undere stimated by factors of up to 20. Synthetic routes to all seven isomers have been developed to provide structural authentication and determin ation of GC response factors.