SOLID-PHASE SYNTHESIS OF O-PHOSPHOROTHIOYLSERINE-CONTAINING AND O-PHOSPHOROTHIOYLTHREONINE-CONTAINING PEPTIDES AS WELL AS OF O-PHOSPHOSERINE-CONTAINING AND O-PHOSPHOTHREONINE-CONTAINING PEPTIDES

This paper describes the synthesis of O-phosphorothioylserine, -threonine, and -tyrosine by sulfurization of the intermediate phosphite triester using phenylacetyl disulfide. Several deprotection procedures were investigated to find the optimal conditions necessary for obtaining the deprotected phosphorothioate amino acids. This method could then be extended to the preparation of O-phosphorothioylserine-and-threonine-containing pentapeptides on a solid phase. After completion of the synthesis of the peptides on the solid support, the amino acid residue containing the free hydroxyl function was phosphitylated using NN-diisopropylbis(4-chlorobenzyl)phosphoramidite and subsequently sulfurized using phenylacetyl disulfide. Silylitic cleavage of the protecting groups, using thiophenol and m-cresol as scavengers, gave the pure deprotected phosphorothioylated peptides. The corresponding phosphopeptides were obtained when the phosphitylated peptides attached to the solid support were oxidized instead of sulfurized using tert-butyl hydroperoxide. To demonstrate that these methods were equally suitable for the synthesis of larger phosphopeptides or phosphorothioate peptides, we prepared the phospho- and the phosphorothioate analog of a pentadecapeptide (H-Leu-Ser-Asp-Gln-Glu-Lys-Arg-Lys-Gln-Ile-Ser-Val-Arg-Gly-Leu-OH) comprising the regulatory phosphorylation site, i.e., serine-14 of phosphorylase b. This example also illustrates that phosphorylation as well as phosphorothioylation is possible of a specified serine residue.