N,N′-Dialkyldiamide-Type Phosphate Protecting Groups for Fmoc Synthesis of Phosphotyrosine-Containing Peptides: Optimization of the Alkyl Group

Abstract
Synthesis and evaluation of three Fmoc–phosphotyrosine derivatives with a phosphate group protected as N,N′-dialkyldiamide (alkyl = Prn, Pri, and Bui) were studied. All the derivatives were obtained as crystals, among which the Buiderivative (4c) was the best in ease of preparation and excellence in cleavage property. Solid phase synthesis of a methionine-containing peptide, H–Tyr(PO3H2)–Val–Pro–Met–Leu–OH, could be done without any problems.