Three phytoalexins, camalexin (C11H8N2S), 6-methoxycamalexin (C12H10N2
SO), and N-methylcamalexin (C12H10N2S), were isolated from shepherd's
purse (Capsella bursa-pastoris) challenged by Alternaria brassicae. N-
methylcamalexin has not been reported previously. Phytoalexin elicitat
ion in shepherd's purse is associated with its resistance to A. brassi
cae, a pathogen which causes an important disease of cruciferous crops
in many parts of the world.