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Spiromastixones A–O, Antibacterial Chlorodepsidones from a Deep-Sea-Derived Spiromastix sp. Fungus

Niu, Siwen, Liu, Dong, Hu, Xinxin, Proksch, Peter, Shao, Zhongzhe, Lin, Wenhan
Journal of natural products 2014 v.77 no.4 pp. 1021-1030
Bacillus subtilis, Bacillus thuringiensis, Enterococcus faecalis, Gram-positive bacteria, Staphylococcus epidermidis, antibiotic resistance, chlorine, culture media, fungi, methicillin, methicillin-resistant Staphylococcus aureus, minimum inhibitory concentration, nuclear magnetic resonance spectroscopy, spectral analysis, structure-activity relationships
Fifteen new depsidone-based analogues named spiromastixones A–O (1–15) were isolated from the fermentation broth of a deep-sea Spiromastix sp. fungus. Their structures were elucidated on the basis of extensive NMR and mass spectroscopic analysis in association with chemical conversion. Spiromastixones A–O are classified into two subtypes based on the orientation of ring C relative to ring A, while the n-propyl substituents on rings A and C are rarely seen in natural products. Most analogues are substituted by various numbers of chlorine atoms. All compounds exhibited significant inhibition against Gram-positive bacteria including Staphylococcus aureus, Bacillus thuringiensis, and Bacillus subtilis with MIC values ranging from 0.125 to 8.0 μg/mL. In addition, compounds 6–10 displayed potent inhibitory effects against methicillin-resistant bacterial strains of S. aureus (MRSA) and S. epidermidis (MRSE), while 10 also inhibited the growth of the vancomycin-resistant bacteria Enterococcus faecalis and E. faecium (VRE). The structure–activity relationships are discussed.