First Total Synthesis and Structure-Activity Relationship of Iheyamide A, an Antitrypanosomal Linear Peptide Isolated from a Dapis sp. Marine Cyanobacterium.

Iheyamide A (1) is an antitrypanosomal linear peptide isolated from a Dapis sp. marine cyanobacterium by our group in 2020, and based on structure-activity relationships of its natural analogues, the C-terminal pyrrolinone moiety has been identified as the phamacophore for its antiparasitic activity. Further, we isolated this pyrrolinone moiety by itself as a new natural product from the marine cyanobacterium and named it iheyanone (2). As expected, iheyanone (2) showed antitrypanosomal activity, but its potency was weaker than iheyamide A (1). To clarify more detailed structure-activity relationships, we completed a total synthesis of iheyamide A (1) along with iheyanone (2) and evaluated the antitrypanosomal activities of several synthetic intermediates. As a result, we found that the longer the peptide chain, the stronger the antitrypanosomal activity. As iheyamide A (1) showed selective toxicity against Trypanosoma brucei rhodesiense, these findings can provide design guidelines for antitrypanosomal drugs.