Efficient synthesis of the 2-aminoimidazolium-bridged diguanosyl intermediate for nonenzymatic primer extension

Nonenzymatic genome replication has yet to be demonstrated experimentally. Recently, studies on the nonenzymatic primer extension mechanism mediated by nucleoside 5′-monophosphates (NMPs) activated with 2-aminoimidazole (2AI) have revealed that imidazolium-bridged dinucleotide intermediates (N * N) are responsible for the bulk of the chemical copying process. As a result, an efficacious synthetic pathway for producing these substrates is desirable. Standard dehydrative redox reaction between NMPs and 2AI can produce N * N in high yields for all homodimers, apart from riboguanosine 5′-monophosphate. Here, we report a vastly improved methodology for the preparation of G * G, by the introduction of a simple reverse-phase cation exchange step to increase the solubility of the mononucleotide. Our approach is more efficient, cost-effective, less time-consuming, and has better atom economy than the currently established methodology for this important molecule in primer extension studies.