In an effort to increase the potency and selectivity of earlier identified substrate-based inhibitors of mitochondrial thymidine kinase 2 (TK-2), we now describe the synthesis of new thymidine analogues containing a 4-or 5-substituted 1, 2, 3-triazol-1-yl substituent at the 3′- position of the 2′-deoxyribofuranosyl ring. These analogues were prepared by Cu-and Ru- catalyzed cycloadditions of 3′-azido-3′-deoxythymidine and the appropriate alkynes, ...