It is also found in barley grainCaffeic acid, which is unrelated to caffeine, is biosynthesized by hydroxylation of coumaroyl ester of quinic acid (esterified through a side chain alcohol). This hydroxylation produces the caffeic acid ester of shikimic acid, which converts to chlorogenic acid. It is the precursor to ferulic acid, coniferyl alcohol, and sinapyl alcohol, all of which are significant building blocks in lignin.[2] The transformation to ferulic acid is catalyzed by the enzyme caffeic acid-O-methyltransferase.
Caffeic acid and its derivative caffeic acid phenethyl ester (CAPE) are produced in many kinds of plants.[8][9][10]