Preparation of an unprotected phosphotyrosine building block and its application in solid-phase synthesis of phosphopeptides

A new and facile synthesis of tyrosine phosphorylated peptides has been developed. Nα-Fmoc-TyrtBu)-OPfp was treated with TFA, phosphorylated with phosphorous oxychloride and the resulting phosphoric acid dichloride was hydrolysed to give Nα-Fmoc-Tyr(PO3H32)-OPfp 1 in an overall yield of 98%. Compound 1 was used in solid-phase peptide synthesis of phosphopeptides 2, 3 and 4, which are fragments of murine adipocyte lipid binding protein. The advantage of using the Pfp ester was the absence of pyrophosphates and other byproducts.