Toxic activity of mimics of the host-specific pathotoxin PM-toxin on corn carrying Texas male-sterile cytoplasm

To investigate the structure-activity relationships of host-specific HMT- and PM-toxins, 8 mimics of PM-toxin A, a component of the host-specific corn pathotoxin produced by Phyllosticta maydis, were synthesized as stereoisomeric mixtures. All the mimics, except for PM-7137, had four β-ketol groups spaced by tri- and tetra-methylenes, which is shorter than the penta-methylenes involved in native PM-toxins. A comparison of their biological activity clearly demonstrated the general structural features necessary for potent activity: four β-ketol groups were necessary with a spacing of chains equal to or longer than penta-methylene.