The tetrahydroisoquinoline (THIQ) ring system is present in a large variety of structurally diverse natural products exhibiting a wide range of biological activities. Routes to mimic the biosynthetic pathways to such alkaloids, by building cascade reactions in vitro, represents a successful strategy and can offer better stereoselectivities than traditional synthetic methods. S-Adenosylmethionine (SAM)-dependent methyltransferases are crucial in the biosynthesis and diversification of THIQs; however, their application is often limited in vitro by the high cost of SAM and low substrate scope. In this study, we describe the use of methyltransferases in vitro in multi-enzyme cascades, including for the generation of SAM in situ. Up to seven enzymes were used for the regioselective diversification of natural and non-natural THIQs on an enzymatic preparative scale. Regioselectivites of the methyltransferases were dependent on the group at C-1 and presence of fluorine in the THIQs. An interesting dual activity was also discovered for the catechol methyltransferases used, which were found to be able to regioselectively methylate two different catechols in a single molecule.
In vitro multi‐enzyme cascade reactions were developed leading to the scalable synthesis of methylated tetra‐hydroisoquinoline alkaloids. The reactions occurred in one‐pot starting from simple building blocks such as dopamine or l‐tyrosine. The use of selected methyltransferases enabled regioselective methylations. When more than one catechol moiety was present, methylations could be directed towards one or more hydroxyl group.
Keywords: alkaloids; biocatalysis; methyltransferases; one-pot cascades; regioselectivity.
© 2021 The Authors. Angewandte Chemie published by Wiley-VCH GmbH.