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

<jats:p> Liquid cultures of <jats:italic>Vibrio</jats:italic> sp. SI9, isolated from the outer tissue of the sea anemone <jats:italic>Radianthus crispus</jats:italic> , was found to produce three new <jats:italic>O</jats:italic> -isocrotonyl-3-hydroxybutyric acid derivatives, <jats:italic>O</jats:italic> -isocrotonyl-3-hydroxypentanoic acid ( <jats:bold>1</jats:bold> ), <jats:italic>O</jats:italic> -isocrotonyl-3-hydroxyhexanoic acid ( <jats:bold>2</jats:bold> ), and <jats:italic>O</jats:italic> -( <jats:italic>Z</jats:italic> )-2-hexenoyl-3-hydroxybutyric acid ( <jats:bold>3</jats:bold> ), together with the known <jats:italic>O</jats:italic> -isocrotonyl-3-hydroxybutyric acid ( <jats:bold>4</jats:bold> ). The structures of <jats:bold>1</jats:bold> – <jats:bold>3</jats:bold> were established by NMR spectroscopy and mass spectrometry, coupled with anisotropy-based chiral analysis, revealing the same <jats:italic>R</jats:italic> -configuration for all congeners <jats:bold>1</jats:bold> – <jats:bold>4</jats:bold> . The compounds <jats:bold>1</jats:bold> – <jats:bold>4</jats:bold> were weakly growth-inhibitory against a marine fish ulcer pathogenic bacterium, <jats:italic>Tenacibaculum maritimum</jats:italic> NBRC16015. Structural similarities among <jats:bold>1</jats:bold> – <jats:bold>4</jats:bold> , the <jats:italic>O</jats:italic> -isocrotonylated 3-hydroxybutyrate oligomers <jats:bold>5</jats:bold> , 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. </jats:p>