PREPARATION OF FLUORO-4-(PHOSPHONOMETHYL)-D,L-PHENYLALANINE AND HYDROXY-4-(PHOSPHONOMETHYL)-D,L-PHENYLALANINE SUITABLY PROTECTED FOR SOLID-PHASE SYNTHESIS OF PEPTIDES CONTAINING HYDROLYTICALLY STABLE ANALOGS OF O-PHOSPHOTYROSINE

4-[(Di-tert-butylphosphono)methyl]-N-(fluoren-9-ylmethoxycarbonyl)-D,L-phenylalanine [O-di-tert-butyl-Pmp-N-Fmoc, 3] has previously been shown to be a useful reagent for the solid-phase synthesis of peptides containing the hydrolytically stable O-phosphotyrosyl mimetic, phosphonomethylphenylalanine (Pmp, 2). One potential limitation of Pmp-containing peptides relative to the corresponding phosphotyrosyl prototypes is the higher pK(a2) value of phosphonic acids as compared to that of phosphates. In an effort to prepare Pmp analogues which more closely approximate phosphotyrosyl residues, O-di-tert-butyl-Pmp-N-Fmoc derivatives were made bearing monofluoro (4), difluoro (5), and hydroxy (6) substituents at the phosphonate methylene. The synthetic utility of analogues 4 and 6 was demonstrated by solid-phase synthesis of the hexameric peptide, H-Gly-X-Val-Pro-Met-Leu-OH, where X = monofluoro Pmp and hydroxy Pmp, respectively. These peptides are analogues of the SH2 recognition motif ''phosphoTyr-Val-Pro-Met-Leu'', which is important for mitogenic cellular signal transduction. The hydrolytic lability of difluoro Pmp analogue 5 precluded its usefulness in peptide synthesis. Along with O-di-tert-butyl-Pmp-N-Fmoc (3), monofluoro (4) and hydroxy (6) derivatives may prove to be useful synthons in the preparation of peptides containing hydrolytically stable analogues of phosphotyrosyl residues.