Thymidine-13C,15N2 is the 13C- and 15N-labeled Thymidine (HY-N1150). Thymidine, a specific precursor of deoxyribonucleic acid, is used as a cell synchronizing agent. Thymidine is a DNA synthesis inhibitor that can arrest cell at G1/S boundary, prior to DNA replication[1][2][3].