Abstract
A pair of geometrically isomeric unsaturated keto fatty acids, (6E,8Z)- and (6E,8E)-5-oxo-6,8-tetradecadienoic acids (1 and 2), were isolated from the culture broth of an actinomycete of the genus Micrococcus, which was associated with a stony coral, Catalaphyllia sp. Their chemical structures were elucidated by spectroscopic analysis including NMR and MS, with special assistance of spin system simulation studies for the assignment of an E geometry at C8 in 2. As metabolites of microbes, compounds 1 and 2 are unprecedented in terms of bearing a 2,4-dienone system. Both 1 and 2 showed antibacterial activity against the plant pathogen Rhizobium radiobacter and the fish pathogen Tenacibaculum maritimum, with a contrasting preference that 1 is more effective to the former strain while 2 is so to the latter. In addition, compounds 1 and 2 displayed agonistic activity against peroxisome proliferator-activated receptors (PPARs) with an isoform specificity towards PPARα and PPARγ.
Highlights
Marine actinobacteria are considered as a potential source for novel natural products with high structural diversity, unique biological activity, and molecular modes of action beneficial to drug development [1,2,3]
Only a handful of natural products such, as strepchloritides [7], nahuoic acids B–E [8], and pteridic acids C–G [9], were obtained from actinobacteria associated with soft corals
There is no report on natural products from actinobacteria residing in stony corals
Summary
Marine actinobacteria are considered as a potential source for novel natural products with high structural diversity, unique biological activity, and molecular modes of action beneficial to drug development [1,2,3]. As a part of our ongoing screening program to discover new natural products from coral-associated bacteria, we have recently reported a catecholate siderophore, labrenzbactin, from an alphaproteobacterium Labrenzia [17] and an unsaturated fatty acid with unique methylation pattern from a gammaproteobacterium Microbulbifer [18].
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