Oxidative steps during the biosynthesis of squalestatin S1Electronic supplementary information (ESI) available: All experimental procedures and analytical data. See DOI: 10.1039/c8sc02615g

The squalestatins are a class of highly complex fungal metabolites which are potent inhibitors of squalene synthase with potential use in the control of cholesterol biosynthesis. Little is known of the chemical steps involved in the construction of the 4,8-dioxa-bicyclo[3.2.1]octane core. Here, using a combination of directed gene knockout and heterologous expression experiments, we show that two putative non-heme-iron-dependent enzymes appear to catalyse a remarkable series of six consecutive oxidations which set up the bioactive core of the squalestatins. This is followed by the action of an unusual copper-dependent oxygenase which introduces a hydroxyl required for later acetylation. Two enzymes of previously unknown function encoded by the squalestatin biosynthetic gene cluster from the fungus Phoma MF5453 catalyse a remarkable series of six consecutive oxidations to form the 4,8-dioxa-bicyclo[3.2.1]octane core of the squalestatins.