Naturally occurring α-pyrones with biological activities are mostly synthesised by polyketide synthases (PKSs) via iterative decarboxylative Claisen condensation steps. Remarkably, we found that some enzymes related to the fatty acid β-oxidation pathway in Escherichia coli, namely CoA ligase FadD and thiolases FadA FadI, can synthesise styrylpyrones phenylpropionic acids vivo. The two directly ...