Antibacterial iminopyrrolidines from Burkholderia plantarii, a bacterial pathogen of rice

Abstract

Burkholderia plantarii, a bacterial pathogen on rice, produced compounds in liquid culture that gave strong inhibitory action against Erwinia amylovora, the bacterium responsible for fire blight disease of apple and pear trees. The active component was hydrophilic and ionic, and was fractionated extensively by passage through SP, DEAE, and LH20 Sephadexes. Final purification was achieved by reverse phase chromatography on C₁₈-bonded silica. Biological activity was associated with two compounds detectable by HPLC (UV λ 218 nm). A third related compound was non-active. The chemical structures of the pure compounds were deduced by NMR and MS, and corroborated by chemical synthesis which also verified the stereochemical assignments. Thus, the two active compounds are reported herewith as 2-imino-3-methylene-5-L(carboxy-L-valyl)-pyrrolidine, and 2-imino-3-methylene-5-L(carboxy-L-threoninyl)-pyrrolidine. The non-active component was deduced to be 2-imino-5-L(carboxy-L-threoninyl)-pyrrolidine.