Turonicin A, an Antifungal Linear Polyene Polyketide from an Australian Streptomyces sp

Turonicin A (1) was isolated from Streptomyces sp. MST-123921, which was recovered from soil collected on the banks of the Turon River in New South Wales, Australia. Turonicin A (1) is an amphoteric linear polyene polyketide featuring independent pentaene and tetraenone chromophores and is structurally related to linearmycins A-C (2-4). The structure of 1 was determined by detailed spectroscopic analysis and comparison to literature data. Bioinformatic analysis of the linearmycin biosynthetic gene cluster also allowed the previously unresolved absolute stereostructures of 2-4 to be elucidated. Turonicin A (1) exhibited very potent activity against the fungi Candida albicans (MIC 0.0031 μg/mL, 2.7 nM) and Saccharomyces cerevisiae (MIC 0.0008 μg/mL, 0.7 nM), moderate activity against the bacteria Bacillus subtilis (MIC 0.097 μg/mL, 85 nM) and Staphylococcus aureus (MIC 0.39 μg/mL, 340 nM), and no cytotoxicity against human fibroblasts, making it an attractive candidate for further development as a potential next-generation antibiotic scaffold.