Importance of 3′-Hydroxyl Group of the Nucleosides for the Reactivity of Thymidine Phosphorylase fromEscherichia coli

Thymidine phosphorylase in phosphate buffer catalyzed the conversion of thymidine to unnatural nucleosides. The 3′-OH, but not the 5′-OH of ribosyl moiety is necessary to be recognized as a substrate. Thus 3′-deoxythymidine could not convert to 5-fluorouracil-2′,3′-dideoxyribose. However, 5′-deoxythymidine was converted to 5-fluorouracil-2′,5′-dideoxyribose.