Antimicrobial Matabolites of Micromonospora SP. BTG10-2 from Narathiwat Peat Swamp soil and Secondary Matabolites of The Endophytic Fungus Exserohilum Rostratum RNAS5

Abstract

In search for bioactive substances of bacteria from soil in Thailand, the ethyl acetate extract of Micromonospora sp. BTG 10-2 from Narathiwat peat swamp soil showed antimicrobial activities against not only the gram-positive bacteria, Micrococcus luteus ATCC 9341 and Bacillus subtilis ATCC 6633 but also the gramnegative bacteria, Pseudomonas aeruginosa ATCC 27853, Eschericia coli ATCC 25922, and Salmonella sp. Bioassay-guided fractionation of the extract resulted in the isolation of an active fraction. Analyses of proton and carbon NMR spectra of the fraction, demonstrated the characteristics of anthraquinones of the chemical composition. The endphytic fungus Exserohilum rostratum RNASS was isolated from the leaf of the Thai medicinal plant, Rhinacanthus nasutus. The ethylacetate extract of the fermentation broth possessed synergistic antifungal activity with ketoconazole against Candida albicans ATCC 10231. Using silica gel quick column and flash column chromatography, two highly symmetrical diketopiperazines, rostratin A and a new exserohilin A, along with a new asymmetrical diketopiperazine, exserohilin B, were isolated from the extract. The structures of those compounds were elucidated by analyses of H, C, 2D-NMR, mass spectra, and x-ray crystallography as well as comparison with the literature data