Process for preparing nucleoside prodrugs

Provided are phosphoramidate nucleoside compounds of Formula (I), or pharmaceutically acceptable salts or esters or solvates thereof, useful in the treatment of cancer, viral infections and other diseases: Also provided is a process for the synthesis of the compounds of Formula (I) where a desired enantiomer, having regard to the asymmetric chiral center of the phosphorus atom P, is provided in an enriched amount. The process comprises admixing a nucleoside with a phosphorochloridate in the presence of a catalyst comprising a metal salt selected from the group consisting of salts of Cu, Fe, La and Yb.