4-Thio-5-bromo-2′-deoxyuridine: chemical synthesis and therapeutic potential of UVA-induced DNA damage

4-Thio-5-bromo-2′-deoxyuridine (3a) is prepared from 5-bromo-2′-deoxyuridine (BrdU) and its key properties are explored. The thionucleoside (3a) can react readily with monobromobimane and produces high fluorescence. 3a has UV maximum absorption at 340 nm and can be incorporated into cellular DNA. The cells containing 3a become sensitive to UVA light, offering therapeutic potential for UVA-induced cell killing.