In Vitro Production of Ergothioneine Isotopologues

Substrate profiling of anion methyltransferases for promiscuous synthesis of S-adenosylmethionine analogs from haloalkanes

Biocatalytic alkylation reactions can be performed with high chemo-, regio- and stereoselectivity using S -adenosyl-l-methionine (SAM)-dependent methyltransferases (MTs) and SAM analogs. Currently, however, this methodology is limited in application due to the rather laborious protocols to access SAM analogs. It has recently been shown that halide methyltransferases (HMTs) enable synthesis and recycling of SAM analogs with readily available haloalkanes as starting material. Here we expand this work by using substrate profiling of the anion MT enzyme family to explore promiscuous SAM analog synthesis. Our study shows that anion MTs are in general very promiscuous with respect to the alkyl chain as well as the halide leaving group. Substrate profiling further suggests that promiscuous anion MTs cluster in sequence space. Next to iodoalkanes, cheaper, less toxic and more available bromoalkanes have been converted and several haloalkanes bearing short alkyl groups, alkyl rings, and functional groups such as alkene, alkyne and aromatic moieties are accepted as substrates. Further, we applied the SAM analogs as electrophiles in enzyme-catalyzed regioselective pyrazole allylation with 3-bromopropene as starting material.

Fluorinated S-Adenosylmethionine as a Reagent for Enzyme-Catalyzed Fluoromethylation

Strategic replacement of protons with fluorine atoms or functional groups with fluorine-containing fragments has proven a powerful strategy to optimize the activity of therapeutic compounds. For this reason, the synthetic chemistry of organofluorides has been the subject of intense development and innovation for many years. By comparison, the literature on fluorine biocatalysis still makes for a slim chapter. Herein we introduce S-adenosylmethionine (SAM) dependent methyltransferases as a new tool for the production of fluorinated compounds. We demonstrate the ability of halide methyltransferases to form fluorinated SAM (S-adenosyl-S-(fluoromethyl)-L-homocysteine) from S-adenosylhomocysteine and fluoromethyliodide. Fluorinated SAM (F-SAM) is too unstable for isolation, but is accepted as a substrate by C-, N- and O-specific methyltransferases for enzyme-catalyzed fluoromethylation of small molecules.

From Natural Methylation to Versatile Alkylations Using Halide Methyltransferases

Halide methyltransferases (HMTs) enable the enzymatic synthesis of S-adenosyl-l-methionine (SAM) from S-adenosyl-l-homocysteine (SAH) and methyl iodide. Characterisation of a range of naturally occurring HMTs and subsequent protein engineering led to HMT variants capable of synthesising ethyl, propyl, and allyl analogues of SAM. Notably, HMTs do not depend on chemical synthesis of methionine analogues, as required by methionine adenosyltransferases (MATs). However, at the moment MATs have a much broader substrate scope than the HMTs. Herein we provide an overview of the discovery and engineering of promiscuous HMTs and how these strategies will pave the way towards a toolbox of HMT variants for versatile chemo- and regioselective biocatalytic alkylations.