Cyclic Tripeptides from the Halotolerant Fungus Aspergillus sclerotiorum PT06-1

Eleven new aspochracin-type cyclic tripeptides, sclerotiotides A-K (1-11), together with three known compounds, JBIR-15 (12), aspochracin (13), and penicillic acid, were isolated from the ethyl acetate extract of the fermentation broth of the halotolerant Aspergillus sclerotiorum PT06-1 in a hypersaline nutrient-rich medium. Their structures were elucidated by spectroscopic analysis and chemical methods. Chemical transformations of 12 and 13 proved that sclerotiotides D K (4-11) were artifacts probably formed during the fermentation or subsequent isolation steps. All 13 cyclic tripeptides have been evaluated for their antimicrobial and cytotoxic effects. Only sclerotiotides A (1), 13 (2), F (6), and I (9) and JBIR-15 (12) showed selective antifungal activity against Candida albicans with MIC values of 7.5, 3.8, 30, 6.7, and 30 mu M, respectively.