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Synthetic reagents for enzyme-catalyzed methylation.

Late-stage methylation is a key technology in the development of pharmaceutical compounds. Methyltransferase biocatalysis may provide powerful options to insert methyl groups into complex molecules with high regio- and chemo-selectivity. The challenge of a large-scale application of methyltransferases is their dependence on S-adenosylmethionine (SAM) as a stoichiometric, and thus exceedingly expensive co-substrate. As a solution to this problem, we and others have explored the use of methyl halides as reagents for in-situ regeneration of SAM. However, the need to handle volatile electrophiles such as methyl iodide (MeI) may also hamper applications at scale. As a more practical solution, we have now developed an enzyme-catalyzed process that affords regeneration of SAM with methyl toluene sulfonate. In this report we describe enzymes from the thiopurine methyltransferase family that accept sulfate- and sulfonate-based methyl donors to convert S-adenosylhomocysteine to SAM with efficiencies that rival MeI-based reactions.