Synthesis of glucosinolate precursors and investigations into the biosynthesis of phenylalkyl- and methylthioalkylglucosinolates.

The alkenyl and aromatic glucosinolates in oilseed rape (Brassica napus) are biosynthesized from chain-extended homologues of protein amino acids, including methionine and phenylalanine. Homologues of these two amino acids, homophenylalanine (2-amino-4-phenylbutyric acid) and dihomomethionine (2-amino-6-methylthiohexanoic acid) were synthesized both with and without a 1-14C label. Microsomal preparations from oilseed rape leaves were shown to contain enzyme systems which metabolize these compounds, with loss of 14CO2, and produce the aldoxime intermediates possible in the biosynthetic pathway utilizing homophenylalanine. These were characterized by comparison with authenticated synthetic compounds. Potential intermediates on the pathway between homophenylalanine and its corresponding aldoxime, the N-hydroxyamino- and the oximino acids, were synthesized and their possible role in the pathway investigated.