Rhabdopeptide/Xenortide-like Peptides from Xenorhabdus innexi with Terminal Amines Showing Potent Antiprotozoal Activity.

Seven new rhabdopeptide/xenortide-like peptides (RXPs) (1-7) with putrescine or ammonia as the C-terminal amines were isolated from Xenorhabdus innexi DSM 16336. Their chemical structures were elucidated by high-resoultion mass spectroscopy (HR-MS) and one-dimensional (1D) and two-dimensional (2D) NMR. They were evaluated for their activities against protozoan parasites and cytotoxicity against rat skeletal myoblasts (L6 cells). All tested compounds exhibited strong effects against Trypanosoma brucei rhodesiense and Plasmodium falciparum, with IC50 values of 0.07-6.25 and 0.091-3.16 μM, respectively, making them the most active RXP derivatives known to date.