Secondary Metabolites And Antimicrobial Activities Of Ascidian-derived Fungus Aspergillus Clavatus

In this paper,the secondary metabolites of Aspergillus clavatus AS-107,which was isolated from fresh tissues of ascidian in Indonesian seawaters,were systematically studied.The crude extracts of secondary metabolites were obtained from static culture and fermentation on rice solid medium.The compounds in the culture extracts were separated and purified by various chromatographic methods and the chemical structures were identified by comprehensive spectroscopic analysis.In addition,the antimicrobial activities of the isolated compounds were evaluated.The metabolites from the culture of the fungal strain A.clavatus AS-107 were purified by reverse phase silica gel column chromatography,normal silica gel column chromatography,preparative thin layer chromatography(TLC),and Sephadex gel column chromatography.Twenty-two compounds(AC1-AC22),including quinazolinone alkaloids,polypeptides,coumarins,terpenoids,and sterols were obtained and identified.The structures were determined by analyzing their physical properties(state,solubility,melting point and color characteristics in the reaction),comprehensive spectral data(NMR,MS,IR,UV,etc.),and by comparing with relevant literatures.Among them,AC1,AC2 and AC3 are new compounds.Moreover,the absolute configurations of AC1 and AC3 were determined by ECD calculation,while AC2 was confirmed by single-crystal X-ray diffraction experiment.The antimicrobial activity of the isolated compounds was tested using two human pathogenic bacteria and five aquatic pathogenic bacteria as pathogenic indicators.The results showed that compounds AC1,AC11,AC13 and AC15 had significant inhibitory effect on Escherichia coli with MIC values of 8,8,4 and 8?g/mL,respectively.Compounds AC1 and AC2 had strong antimicrobial activity against Micrococcus luteus with the same MIC value of 8 ?g/mL.Compound AC13 had bacteriostatic activity against Vibrio anguillarum with MIC value of 8 ?g/mL,while compound AC1 had significant bacteriostatic effect on Aeromonas hydrophilawith MIC value of 4 ?g/mL.Compound AC11 had certain inhibitory effect on Vibrio harveyi with MIC value of 8 ?g/mL.Compounds AC11,AC13 and AC15 have obvious inhibitory effect on Pseudomonas aeruginosa with MIC values of 8,4 and 4?g/mL,respectively.The above results indicated that compounds AC1,AC2 and AC13 had inhibitory effects on all of the seven tested pathogenic bacteria,which deserve to be further studied.Based on the analysis of the structure-activity relationship of the tested compounds,it showed that compared with compound AC15,AC1 had stronger antibacterial activity when the ester bond was opened.Compared with compound AC3,the different configuration at C-27 of AC14 led to variation of antibacterial activity.The results of this study further enriched the chemical diversity of marine natural products.The obtained compounds AC1,AC2,AC11,AC13 and AC15 had good antimicrobial activity,which provided the theoretical and applied basis for the possible development of marine bioresources.