Used in peptide synthesis as a protected phosphorylated tyrosine building block. The Boc group provides N-terminal protection, while the phosphate group is in its free acidic form (as a monoester), supplied as the DIPEA salt for improved solubility and handling. This makes it suitable for solid-phase or solution-phase assembly of phosphopeptides. Commonly applied in the preparation of biologically active peptides that require tyrosine phosphorylation for function, such as substrates for kinases or signaling molecules.