It was hypothesized by a computational similarity search that this moiety would fit best in the hydrophobic binding pocket of cathepsin B. After successfully synthesizing numerous candidates, including compound 6 (Figure 4), it appeared that this cyclobutane‐containing linker showed greater selectivity towards cathepsin B over other enzymes, increasing its selectivity towards tumor cells compared to valine‐citrulline linker systems that are already in clinical trials.[48]. This evidence concerns the gene CTSB and neoplasm.