Clofarabine Mixture 4_5

Clofarabine Mixture 4_5 is a positional isomer impurity arising from chloro-substitution at the 4- and 5-positions of the furanose ring in the Clofarabine core structure. It retains the pyrimidine heterocycle and phosphonamidate functionalities but exhibits distinct regiochemical substitution patterns due to synthetic pathway divergence. The compound features a chlorinated furanose moiety linked to a 1-(2-deoxy-β-D-ribofuranosyl)pyrimidin-2,4-dione scaffold. This impurity forms during oxidative chlorination steps, competing with the parent drug’s formation. It serves as an HPLC reference standard for quantifying regioisomeric impurities in Clofarabine API batches.