The chemoproteomic analyses of the CAII hits revealed that they engaged CAII in cells, however, at low stoichiometry, likely due to the low kinact rates for these hits. The two CAII hits and the negative control were also found to interact with many additional proteins in cells (>100), many of which were common to all three SF compounds. This highlighted that specificity is likely to be a key challenge to overcome when developing SF-based inhibitors. Previous work in our group has demonstrated that the reactivity of the SF electrophile is highly tuneable. Therefore, it is anticipated that selective target engagement in cells would be achievable through reduction of the intrinsic reactivity of the SF, while optimising kinact and KI for the target. The HTC-D2B approach described here provides a useful strategy for performing this optimisation.