Design, semi-synthesis of soft coral-derived Aspergillus sp. secondary metabolite geodin derivatives and their antibacterial activities

Abstract

A series of novel ester derivatives 2 − 7, of natural product geodin 1, isolated from the soft coral-derived fungus Aspergillus sp., were designed and semi-synthesised through one step reaction with high yield. Compound 5 showed strong antifouling inhibitory activities with MIC of 4.80 μM while compound 4 showed selective inhibitory activities with MICs values 8.59 μM against Aeromonas salmonicida and Pseudomonas aeruginosa (Sea-Nine 211, MIC = 0.27 μM). Compounds 3, 4 and 6 showed potent anti-pathogenic inhibitory activities with MICs of 2.29 μM, 4.29 μM and 4.56 μM respectively against Staphylococcus aureus (Ciprofloxacin, MIC = 0.156 μM). Compound 2 showed weak inhibitory activity against A. salmonicida with MIC 18.75 μM (Sea-Nine 211, MIC = 0.27 μM) and with MICs 9.38 μM against S. aureus (ciprofloxacin, MIC = 0.156 μM). However, compound 7 showed very low antibacterial activities with MIC = >20 μM. The preliminary structure-activity relationships of compounds 2 − 7 further prove that the modification of 4-OH group of natural product geodin 1 improves the antibacterial activities such as antifouling and anti-pathogenic activities.