Eurystatins A and B, new prolyl endopeptidase inhibitors. I. Taxonomy, production, isolation and biological activities.

Eurystatins A and B, were isolated from the cultured broth of Streptomyces eurythermus R353-21. They showed specific and potent inhibitory activity against prolyl endopeptidase and did not show antimicrobial activity. No lethal toxicity was observed for the two compounds after ip administration in mice at 200 mg/kg.