- Phosphatidylinositol (PI) is the biosynthetic precursor for seven phosphoinositides, important signaling lipids in cells. We synthesized a membrane-permeant caged PI derivative featuring a photo-removable coumarinyl group masking the negative charge of the phosphate as well as two enzymatically removable butyrate esters for increased lipophilicity and for preventing phosphate migration. We demonstrated rapid cell entry and cellular labeling in fixed cells via a photo-crosslinkable diazirine followed by attachment of a fluorophore through click chemistry. Using this technique, we found that the multifunctional caged PI derivative resided predominantly at internal membranes but rapidly changed to the plasma membrane after uncaging. Accordingly, a preliminary proteomic analysis of the lipid-protein conjugates revealed that the two major PI transport proteins PITPα and β were prime targets of the photo-crosslinked PI derivative.