A pre-prodrug of 5-fluorouracil (5-FU). After oral uptake, capecitabine is first metabolized to 5'-deoxy-5-fluorocytidine (5'-DFCR), which occurs mainly in the liver by carboxyl-esterase. The metabolite is converted to 5'-deoxy-5-fluoro-uridine (5'-DFUR) by cytidine deaminase in liver and tumor tissue. Then 5'-DFUR is converted to 5-FU intracellularly by thymidine phosphorylase, which is often expressed in tumor tissue. MW: 359.35. Purity ≥99% by HPLC