Further investigation of the off-targets revealed that some proteins were competed in the presence of parent, indicating high levels of engagement; these included: FABP5, PEBP1, ABHD6, and LYPLA1. (Fig. &). ABHD6 and LYPLA1 catalyse the hydrolysis of esters and thioesters, respectively, and have nucleophilic catalytic residues which are likely to react with the SF moiety. Similarly, PEBP1 is a phospholipid binder, and is the prototype of a novel family of serine protease inhibitors. More specifically, each of these proteins bind molecules containing hydrophobic alkyl chains, consistent with previous reports involving SF-containing probes targeting FABP5 in cells. The high levels of occupancy at these targets suggests they may be amenable to the development of potent SF-based covalent inhibitors.