Demonstration of a Scalable One-Pot Synthesis of Fmoc‑O‑Benzylphospho‑l‑serine

A cost-effective one-pot synthesis of Fmoc-O-benzylphospho-l-serine, an amino acid commonly used in the synthesis of phosphorylated peptides, has been developed. Two methods for executing this synthesis are described, and both have been scaled to provide kilogram quantities of the title compound in ∼50% isolated yield. Development of both processes has led to the identification of crystallization conditions which provide the product as a solvate with high purity. An efficient process for generating the solvent-free product from the solvate has also been developed.