Den enkelte substitution af klorin med hydrogen ved position 2 adskiller cladribine fra dets naturlige modpart 2 '- deoxyadenosin og gør molekylet resistent over for deaminering ved adenosin deaminase.
The single substitution of chlorine for hydrogen at position 2 distinguishes cladribine from its natural counterpart 2'-deoxyadenosine and renders the molecule resistant to deamination by adenosine deaminase.