Abstract A novel type of hydrophilic 5-tethered carborane-containing 2′-deoxyuridine derivative, SUB-7-DIOL, has been developed. This compound is a potential agent for DNA incorporation and BNCT, because it showed satisfactory aqueous solubility and demonstrated an excellent rate of phosphorylation by human thymidine kinase. This study also demonstrated the importance of tethering a flexible hydrocarbon chain between the ...