Azidomethyl-dU (AmdU) is a nucleoside that contains an azide group. The structure of the nucleoside is similar to thymidine, and it is incorporated into nascent DNA by cellular polymerases, similar to EdU.
In contrast to EdU which needs to be further modified with azides in the presence of the copper catalyst, AmdU can also react in the absence of copper catalyst using SPAAC click chemistry with strained cycloalkynes, such as cyclooctynes. This enables the detection of nascent DNA in benign, copper-free conditions.
