PREPARATION OF O-PHOSPHOTYROSINE-CONTAINING PEPTIDES BY FMOC SOLID-PHASE SYNTHESIS - EVALUATION OF SEVERAL FMOC-TYR(PO(3)R(2))-OH DERIVATIVES

The synthesis of two model Tyr(P)-containing peptides using Fmoc-Tyr(PO(3)tBu(2))-OH, Fmoc-Tyr(PO(3)Bzl(2))-OH and Fmoc-Tyr(PO3H2)-OH established that the t-butylphosphate-protected derivative was the preferred derivative for use in Fmoc solid-phase peptide synthesis, since it afforded phosphopeptides in high purity and with the lowest amount of Tyr-peptide contamination. In addition, this study confirmed that commercially available Fmoc-Tyr(PO3H2)-OH is also suitable for use in Fmoc solid-phase synthesis but gives less pure phosphopeptides, along with the generation of 1-4% of the tyrosine-containing peptide for the model sequences studied. In view of the good performance of Fmoc-Tyr(PO(3)tBu(2))-OH, a 'large-scale' three-step synthetic procedure was developed which involved phenacyl protection of the carboxyl group, 'phosphite-triester' phosphorylation of the tyrosyl hydroxyl using di-t-butyl N,N-diethylphosphoramidite, and final removal of the phenacyl group by zinc reduction in acetic acid.