dUDP is a deoxyribonucleotide made from UDP in the reaction catalyzed by ribonucleotide reductase, as follows:

UDP + NADPH <=> dUDP + NADP⁺

Phosphorylation of dUDP yields dUTP. dUTP is quickly cleaved in cells by dUTPase to yield dUMP. This reaction is part of the de novo synthetic pathway for dTTP.