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S‐adenosylmethionine: studies on chemical and enzymatic synthesis

Several methods for the chemical and enzymatic synthesis of (‐)‐S‐adenosylmethionine (AdoMet) are described and compared. Studies on the effects of solvents, pH, methylating reagents, and KI on the coupling of sodium homocysteine thiolate and 5′‐chloro‐5′‐deoxyadenosine led to an improved procedure for the synthesis of (+/‐)‐AdoMet. The use of trimethylsulfonium iodide as a methylating agent under acidic conditions results in a higher content of the desired (‐)‐epimer than does the use of CH3I. The enzymatic synthesis of (‐)‐AdoMet using AdoMet synthetase from an over‐producing strain of Escherichia coli is demonstrated and the effect of product inhibition on preparative‐scale synthesis is illustrated. A new HPLC technique for separation of the epimeric mixture of AdoMet, which allows small‐scale preparation of optically pure AdoMet from the enzyme product, has been developed. With this HPLC technique, evidence that (‐)‐AdoMet is the sole epimer formed by the enzyme has been shown.