N2‐Substituted 2′‐Deoxyguanosine Triphosphate Derivatives as Selective Substrates for Human DNA Polymerase κ

N²‐Alkyl‐2′‐deoxyguanosine triphosphate (N²‐alkyl‐dGTP) derivatives with methyl, butyl, benzyl, or 4‐ethynylbenzyl substituents were prepared and tested as substrates for human DNA polymerases. N²‐Benzyl‐dGTP was equal to dGTP as a substrate for DNA polymerase κ (pol κ), but was a poor substrate for pols β, δ, η, ι, or ν. In vivo reactivity was evaluated through incubation of N²‐4‐ethynylbenzyl‐dG with wild‐type and pol κ deficient mouse embryonic fibroblasts. CuAAC reaction with 5(6)‐FAM‐azide demonstrated that only cells containing pol κ were able to incorporate N²‐4‐ethynylbenzyl‐dG into the nucleus. This is the first instance of a Y‐family‐polymerase‐specific dNTP, and this method could be used to probe the activity of pol κ in vivo.