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 Nocardia ignorata, isolated from the terrestrial lichen Collema auriforme , 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) ( 1 ), cyclo (l-Pro-l-Tyr) ( 2 ), cyclo (d-Pro-l-Tyr) ( 3 ), cyclo (l-Pro-l-Val) ( 4 ), cyclo (l-Pro-l-Leu) ( 5 ), and one auxin derivative: indole-carboxaldehyde ( 8 ) were isolated, along with two new brominated diketopiperazines: cyclo (d-Pro-l-Br-Tyr) ( 6 ) and cyclo (l-Pro-l-Br-Tyr) ( 7 ). Structure elucidation was performed using HRMS and 1D and 2D NMR analysis, and the synthesis of compounds 6 and 7 was carried out in order to confirm their structure.