Isolation and Structure Identification of Novel Brominated Diketopiperazines from Nocardia ignorata-A Lichen-Associated Actinobacterium.

Actinobacteria are well known for their potential in biotechnology and their production of metabolites of interest. Lichens are a promising source of new bacterial strains, especially Actinobacteria, which afford a broad chemical diversity. In this context, the culture medium of the actinobacterium isolated from the terrestrial lichen , was studied. The strain was cultivated in a BioFlo 115 bioreactor, and the culture medium was extracted using an XAD7HP resin. Five known diketopiperazines: cyclo (l-Pro-l-OMet) (), cyclo (l-Pro-l-Tyr) (), cyclo (d-Pro-l-Tyr) (), cyclo (l-Pro-l-Val) (), cyclo (l-Pro-l-Leu) (), and one auxin derivative: indole-carboxaldehyde () were isolated, along with two new brominated diketopiperazines: cyclo (d-Pro-l-Br-Tyr) () and cyclo (l-Pro-l-Br-Tyr) (). Structure elucidation was performed using HRMS and 1D and 2D NMR analysis, and the synthesis of compounds and was carried out in order to confirm their structure.