5-(4-(4-(Prop-2-yn-1-yloxy)benzoyl)phenoxy)pentanoic acid is a trifunctional building block for chemical probe synthesis, typically employed for photoaffinity labeling in chemcial biology and medicinal chemistry. It contains a light-activated benzophenone (photoreactive group), terminal alkyne tag (clickable handle), and carboxylic acid synthetic handle (connectivity group). When appended to a ligand or pharmacophore through its acid linker, this probe building block allows for UV light-induced covalent modification of a biological target with potential for downstream applications via the alkyne tag.
Tandem photoaffinity labeling–bioorthogonal conjugation in medicinal chemistry.
A library approach to rapidly discover photoaffinity probes of the mRNA decapping scavenger enzyme DcpS. 
 M.Van Scherpenzeel, et al, Chembiochem, 2009, 10(10), pp 1724-1733.