Photochemical dimerization of wasalexins in UV-irradiated Thellungiella halophila and in vitro generates unique cruciferous phytoalexins

The production of biswasalexins A1 and A2 in sodium chloride and UV stressed salt cress plants, as well as their chemical syntheses and antifungal activity against four cruciferous pathogens is reported. Biswasalexins A1 and A2 are cruciferous phytoalexins whose formation in planta appears to result from a photochemical reaction that might protect the plant from fungal pathogens and UV-radiation. The production of phytoalexins in Thellungiella halophila exposed to UV-radiation and NaCl was investigated over a period of 8 days. UV-radiation induced substantially larger quantities of wasalexins A and B than NaCl irrigation or CuCl 2 spray. Isolation of two metabolites and their chemical structure determination using X-ray diffraction analysis provided the phytoalexins biswasalexins A1 and A2, that resulted from head-to-tail photodimerization of wasalexin A. The production of biswasalexins A1 and A2 in stressed T. halophila, as well as their chemical synthesis and antifungal activity are reported. Biswasalexins A1 and A2 (60 nmol/g and 15 nmol/g fresh wt, respectively, 2 days after UV elicitation) are cruciferous phytoalexins whose formation in planta appears to result from a photochemical reaction, which might protect the plant from fungal attack and UV-radiation.