Fragments of associative heterodimers are quite frequently linked to one another using methylene or polymethylenic linkers. However, heterodimers for which the constituting pharmacophoric agents act on molecular targets quite distinct in nature such as antibody drug conjugates (ADC), the use of a cleavable linker is preferred over a non-cleavable methylenic linker. Of paramount importance is the choice of linkers as they must be stable in systemic circulation in order to avoid unwanted side effects, systemic toxicity and reduction in therapeutic index, and be easily cleaved once inside the target cell for an efficient delivery of the drug(s).