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5''-Ethynyl-2''-deoxycytidine (EdC) is a nucleoside analog that inhibits replication of the herpes simplex virus-1 (HSV-1) KOS strain (ID₅₀ = 0.2 μg/mL). It also reduces virus-induced cytopathogenicity of HSV-1, HSV-2, and vaccinia virus strains in PRK cells (MICs = 0.2-0.4, 1-2, and 5 μg/ml, respectively). EdC is an inhibitor of thymidylate synthetase, selectively reducing DNA incorporation of [1'',2''-³H]deoxyuridine over [CH₃-³H]deoxythymidine in PRK cells (ID₅₀s = 3 and 120 μg/ml, respectively). It inhibits thymidine synthetase in and reduces proliferation of L1210 cells, an effect which is reversed by addition of deoxythymidine (ID₅₀s = 4.4 and 1,000 μg/ml, respectively). EdC has been used to monitor DNA synthesis and cellular replication via click chemistry conjugation of the ethynyl group to an azido group of various fluorochromes.

5-Ethynyl-2’-deoxycytidine is an lower toxicity analog of 2’-deoxycytidine, a metabolic labeling probe for DNA synthesis. 5-Ethynyl-2’-deoxycytidine is most commonly used when thymidine analogs is undesirable.