The establishment of structure activity relationship (SAR) for rakicidin derivatives is pretty vital to develop rakicidins as a new type of anti-cancer agents. Herein, two novel rakicidin derivatives, compounds B1-1 (1) and B1-2 (2), a cyclic depsipeptide and a chain lipopeptide, respectively, were isolated from culture broth of Micromonospora chalcea FIM-R160609, and their structures were elucidated clearly by extensive NMR and HR-ESI-MS analyses. Following, their cytotoxic activities were evaluated against HCT-8 and PANC-1 human cancer cell lines under hypoxic and normoxic conditions. Their activities were significantly decreased when compared with that of rakicidin B1. These results demonstrated that the double bond located on the position 9 and 10 of conjugated diene unit and cycle-type structure plays an important role in keeping the biological activity of rakicidins. Furthermore, the positive effect of double bond and cycle form on the anti-bacterial activities were also confirmed by testing their inhibitory activities against gram positive bacteria. This work will definitely diversify the SAR of rakicidins and provide the guidance for the design of new potent rakicidin analogues.
Keywords: Micromonospora chalcea FIM-R160609; antibacterial activity; hypoxia-selective cytotoxicity; rakicidin; structure elucidation.