Synthesis of both [¹⁴C-1] labelled and unlabelled non-protein amino acids has allowed investigation of the early steps of glucosinolate biosynthetic pathway in Brassica napus. Use of the [¹⁴C-1]amino acids has allowed limited characterisation of the enzymes involved in the initial oxidative decarboxylation reaction. The intermediates between the amino acid and the aldoxime have been studied by synthesis of a range of potential intermediates. Synthesis of [²H-2]homophenylalanine has allowed preliminary investigations into the intermediates by examination of the retention or loss of the label in the aldoxime product. The use of 19F NMR as a technique to examine the intermediates as they are formed in situ has been investigated with synthesis of a range of fluorine substituted amino acids and aldoximes. Synthesis of a range of unlabelled and [¹⁴C-1] methionine homologues has allowed investigation of the enzymes involved in aliphatic glucosinolate biosynthesis. The synthesis of a range of dihomomethionine analogues, and subsequent competition assays have outlined the substrate specificity of the aliphatic enzyme, and allowed the development of a crude active site model. The biosynthesis of thiohydroximates from aldoximes has been investigated, by examining the C-S bond cleavage which takes place during thiohydroximate formation. Investigation of these enzymes required the synthesis of the proposed intermediate, a cysteine thiohydroximate conjugate. This was accomplished using nitrile oxide methodology. Use of regiospecific deuteration has allowed the synthesis of deuterated homophenylalanines, which will allow further investigation of the pathway. [¹⁴C-1]Dihomomethionine has been synthesised to investigate the possibility of its incorporation into 2-propenylglucosinolate.