Identification bioactive compounds from marine microorganism and exploration of structure activity relationships

Marine natural products (MNPs) have become new strong leads for antimicrobial drug discovery and an effective alternative to control drug resistant infections. Herein we report the bioassay guided fractionation of marine extracts from sponges Lendenfeldia, Ircinia and Dysidea that led us to identify novel compounds with antimicrobial properties. Tertiary amines or quaternary amine salts: anilines 1, benzylamines 2, tertiary amines 3 and 4, and quaternary amine salt 5, along with three known compounds (6-8) were isolated from a crude extract and MeOH eluent marine extracts. The absolute configurations of the new compounds were assigned based on tandem mass spectrometry (MS) analysis. Several of the compounds exhibited potent in-vitro antibacterial activity, especially against Methicillin-resistant Staphylococcus aureus (MRSA) (MICs from 15.6 to 62.5 micro g/mL). Herein, we also, report structure activity relationships of a diverse range of commercial structurally similar compounds. The structure activity relationships (SARs) results clearly demonstrate that modification of the amines through linear chain length, and inclusion of aromatic rings, modifies the observed antimicrobial activity towards different biological activity. Several commercially available compounds, which are structurally related to the molecules we discovered showed broad spectrum antimicrobial activity against different test pathogens with an MIC50 range of 50 to 0.01 micro M. The results of cross-referencing antimicrobial activity and cytotoxicity establish that these compounds are promising potential lead molecules, with a favourable therapeutic index for antimicrobial drug development. Additionally, the SAR studies show that simplified analogues of the isolated compounds with increased bioactivity