Cytochalasins - Structure-activity-relationships

Seven cytochalasins, 17-O-acetylcytochalasin A and two derivatives of cytochalasin B were assayed for Pseudomonas syringae, Bacillus megaterium, and for Geotrichum candidum. Their ability to inhibit the growth of tomato seedlings and their toxicity to brine shrimp (% larvae mortality were also investigated. Among the compounds assayed only cytochalasin A showed antibiotic and fungicidal activity. Toxicity to tomato seedlings was exhibited by both [14]- and [11]-macrocyclic cytochalasans, while the activity decreased in the derivatives acetylated on the 7-hydroxy group and markedly in cytochalasin E. In the brine shrimp bioassay, cytochalasin E was the most active mycotoxin, but generally, at low concentrations, the cytochalasins with the [11]-macrocyclic ring were more active than those with the [14]-macrocyclic ring; cytochalasin A appeared to be the most toxic.