Abstract Two novel modified 2′-deoxyuridine triphosphates carrying an azide functionality linked to the nucleobase were synthesized. For probing the sterical influence on enzymatic incorporation and Staudinger ligation, differently sized flexible linkers were chosen. Both nucleotides can completely replace natural thymidine in primer extension as well as polymerase chain reaction (PCR) using Pyrococcus woesei DNA polymerase. For PCR ...