XR330

The nocazines are a newly defined family of antibacterial and cytotoxic cyclic dipeptides produced by different actinobacterial species. Here, we identify a nocazine biosynthetic gene cluster in Nocardiopsis dassonvillei and describe the elucidation of the biosynthetic pathway leading to the nocazine family members nocazine E and XR334. Diketopiperazine (DKP) formation is carried out by a tRNA-dependent cyclodipeptide synthase (CDPS) showing an unknown product profile, while tailoring of the DKP-scaffold is achieved through the combined and combinatorial action of a cyclodipeptide oxidase and two distinct SAM-dependent O-/N-methyltransferases. Our results help to illuminate the biosynthetic logic resulting in the structural diversity of the nocazine family and set the stage for exploring the biological function of modified cyclic dipeptides as possible mediators of host-pathogen and host-parasite interactions.

Two diketopiperazines, XR334 (1) and the novel compound XR330 (2), were isolated from the lyophilised biomass of an unidentified Streptomyces sp. Their structures were elucidated on the basis of spectroscopic studies and confirmed by chemical synthesis. Both compounds inhibited plasminogen activator inhibitor-1 activity in an amidolytic assay of tissue plasminogen activator mediated plasmin generation. Compound 1 also enhanced fibrinolysis ex vivo and protected against thrombus formation in the rat. These diketopiperazines represent the first low molecular weight inhibitors of plasminogen activator inhibitor-1, a physiological regulator of fibrinolysis.