Biosynthesis of phenylpropanoid compounds. Part I. Biosynthesis of eugenol in Ocimum basilicum L

Abstract

L-Phenylalanine and cinnamic acid, but not L-tyrosine, have been found to be precursors of eugenol (4-allyl-2-methoxyphenol) in Ocimum basilicum. Separate feeding experiments with [1-¹⁴C,G-³H]-, [2-¹⁴C,G-³H]-, and [3-¹⁴C,G-³H]-phenylalanine have shown that the carboxylic carbon atom of the amino-acid is lost during the biosynthesis of eugenol (probably at the ferulic acid level), and an extra one-carbon unit is introduced into the allyl group. [2-¹⁴C]- and [3-¹⁴C]Phenylalanine have been shown to be incorporated specifically into eugenol by unambiguous degradations of the isolated allylphenol; these results indicate that the foregoing decarboxylation and C₁ introduction involve no rearrangement of the side chain of phenylalanine (and, by implication, of cinnamic acid precursors). Evidence is given that the other allylphenols of O. basilicum, i.e. estragole and chavicol, are biosynthesized in the same manner as eugenol.