Thesis (M.Sc.)--Chulalongkorn University, 2003

The purpose of this research was to study bioactive compounds from endophytic fungi isolated from Croton oblongifolius, Thai medicinal plant. Plant samples were collected from Kui Buri District, Prachuap Khiri Khan Province. Fungal endophytes were isolated from leaves, branches, and bark sections by surface sterilization method and placed on malt extract agar. In total 62 fungal isolates were obtained and tested for the production of antimicrobial compounds. Fungal isolate PcBr20 was chosen for the further study of bioactive compounds because this isolate produced the compounds that were active against a large number of test microorganisms. Based on morphology and nucleotide sequencing of ITS regions of rDNA, isolate PcBr20 was identified as Fusarium sp. (Anamorph) or Gibberella sacchari (Telemorph), respectively. Chromatographic techniques and crystallization were used to isolate bioactive compounds from malt extract culture broth. Structure elucidation of the pure compounds were investigated using physical properties and spectroscopic techniques. Two compounds were isolated, a mixture of fusaric acid and dehydrofusaric acid (mixture BH1) and compound BE1 which was a white amorphous solid (mp. 190-191 ํC). The structures of compound BE1 are still under investigation. Antimicrobial activities of pure compounds were tested. It was found that a mixture of fusaric acid and dehydrofusaric acid exhibited against Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Saccharomyces cerivisiae TISTR 5169, Candida albicans ATCC 10231, and Trichophyton mentagrophyte with MIC value of 0.98, 62.50, 15.62, 1x10[superscript 3], 62.50, 1x10[superscript 3] and 1x10[superscript 3] microgram/ml, respectively and compound BE1 showed against B. subtilis ATCC 6633, S. aureus ATCC 25923, E. coli ATCC 25922, and P. aeruginosa ATCC 27853 with MIC value of 0.98, 62.50, 62.50 and 1x10[superscript 3] microgram/ml, respectively.