Three new O -isocrotonyl-3-hydroxybutyric acid congeners produced by a sea anemone-derived marine bacterium of the genus Vibrio

Liquid cultures of Vibrio sp. SI9, isolated from the outer tissue of the sea anemone Radianthus crispus , was found to produce three new O -isocrotonyl-3-hydroxybutyric acid derivatives, O -isocrotonyl-3-hydroxypentanoic acid ( 1 ), O -isocrotonyl-3-hydroxyhexanoic acid ( 2 ), and O -( Z )-2-hexenoyl-3-hydroxybutyric acid ( 3 ), together with the known O -isocrotonyl-3-hydroxybutyric acid ( 4 ). The structures of 1 – 3 were established by NMR spectroscopy and mass spectrometry, coupled with anisotropy-based chiral analysis, revealing the same R -configuration for all congeners 1 – 4 . The compounds 1 – 4 were weakly growth-inhibitory against a marine fish ulcer pathogenic bacterium, Tenacibaculum maritimum NBRC16015. Structural similarities among 1 – 4 , the O -isocrotonylated 3-hydroxybutyrate oligomers 5 , and microbial biopolymer polyhydroxyalkanoates (PHA) suggest the presence of a common biosynthetic machinery, and hence a possible dehydrative modification at the hydroxy terminus of PHA.