Ultraviolet-mediated antibiotic activity of species of Compositae caused by polyacetylenic compounds

A survey of North, Central, and South American composites, and of certain polyacetylenic compounds occurring in them, confirmed that the ultraviolet-mediated antibiotic activity against Candida albicans can be ascribed to the presence of particular polyacetylenes and their thiophene derivatives. Leaves, stems, roots, and achenes were assayed separately. An attempt was made to relate the phototoxic activity of specific compounds to their chemical structures. Most composites tested were not phototoxic against Candida, but many were antibiotic. The antibiotic activity also appears to be caused by polyacetylenes. Of 65 sequiterpene lactones assayed, only a few were found to be antibiotic, and only one, glaucolide G, was phototoxic.