New synthesis of D,L-Fmoc protected 4-phosphonomethylphenylalanine derivatives and their enzymatic resolution

A new synthesis of N-Fmoc 4-phosphonomethyl-D,L-phenylalanine protected under di-tert-butyl or dimethyl phosphonate forms (Fmoc-Pmp(OR)(2)), suitable for solid phase peptide synthesis is described. Resolution of these hydrolytically stable analogs of O-phosphotyrosine was tried either by fractional recrystallization of diastereoisomeric salts or by using the subtilisin Carlsberg esterase. Only the enzymatic resolution of ethyl 4-[(dimethylphosphono)methyl]-D-L-phenylanine succeeded. These results are discussed by comparison with the literature data. The L and D amino acids were used to prepare separately, through solid-phase peptide synthesis, followed by deprotection of dimethylphosphonate group by trimethylsilyliodide (TMSI) in acetonitrile, the L and D isomers of Glu-Asp-Val-Pmp-Glu-Asn-Leu-His-Thr, a peptide corresponding to a potentially phosphorylated site of the phosphatase PTP 1C.