Insight into lipophilicity of deoxyribonucleoside-boron cluster conjugates

Lipophilicity was investigated for 20 2'-deoxyribonucleoside derivatives modified with electron-neutral 1,2-dicarba-closo-dodecaborane, 1,12-dicarba-closo-dodecaborane, 7,8-dicarba-nido-undecaborate anion, and metallacarborane containing Co, Fe, or Cr. The partition coefficient (P) for neutral conjugates and the distribution coefficient (D-7.4) for ionic compounds were determined as a lipophilicity descriptor using a shake-flask method. All modified nucleosides had P/D-7.4 values higher than those of an appropriate unmodified 2'-closo-dodecaborane and metallacarborane was found to be three orders of magnitude higher than that of its unmodified counterpart. The lowest impact on the P/D-7.4 values of the conjugates was observed for the 7,8-dicarba-nidoundecaborate anion. A preliminary molecular modeling study of a thymidine-carborane conjugate with beta-cyclodextrin confirmed the ability of the components to form an inclusion complex.