Enzymatic cis-Decalin Formation in Natural Product Biosynthesis

Stereoselective synthesis of cis-decalin structures using [4 + 2] cycloaddition is challenging. We explored the biosynthetic pathway of the fungal natural product fischerin (1) to identify a new pericyclase FinI that can catalyze such a reaction. The cocrystal structure of FinI, a predicted O-methyltransferase, with the product and SAM provides insight into cis-decalin formation in nature.