Synthesis of S-adenosyl-L-methionine analogs and their use for sequence-specific transalkylation of DNA by methyltransferases

Here we describe a one-step synthetic procedure for the preparation of S-adenosyl-L-methionine (AdoMet) analogs with extended carbon chains replacing the methyl group. These AdoMet analogs function as efficient cofactors for DNA methyltransferases (MTases), and we provide a protocol for sequence-specific transfer of extended side chains from these AdoMet analogs to DNA by DNA MTases. Direct chemoselective allylation or propargylation of S-adenosyl-L-homocysteine (AdoHcy) at sulfur is achieved under the acidic conditions needed to protect other nucleophilic positions in AdoHcy. The unsaturated bonds in beta position to the sulfonium center of the resulting AdoMet analogs are designed to stabilize the transition state formed upon DNA MTase-catalyzed nucleophilic attack at the carbon next to the sulfonium center and lead to efficient transfer of the extended side chains to DNA. Using these protocols, sequence-specific functionalized DNA can be obtained within one to two weeks.