UV-irradiation of sliced stem tubers of kohlrabi (Brassica oleracea var. gongylodes) followed by incubation for 4 days, resulted in the production of two new sulphur-containing indole phytoalexins, cyclobrassinone and 1 -methoxyspirobrassinin, whose structures were elucidated on the basis of spectroscopic data. Three known indole phytoalexins, spirobrassinin, methoxybrassitin and methoxybrassinin, and several m inor phytoalexin-like compounds not yet identified were also isolated. The accumulation of these indole phytoalexins was also induced by abiotic elicitation with CuCl2.
Feeding both of L-[β-14C]tryptophan and L-[14CH3]methionine to UV-irradiated stem tuber tissue of kohlrabi indicated that the S-containing indole phytoalexins were biosynthesized from these amino acids.