N in -Diphenylphosphinothioyltryptophan, a useful derivative for peptide synthesis by the methanesulphonic acid–thioanisole system and fluoride ion deprotection methods

The diphenylphosphinothioyl (Ppt) group attached at the Nin function of tryptophan can be smoothly removed not only by 0.25 M methanesulphonic acid–thioanisole in trifluoroacetic acid, but also by tetra-n-butylammonium fluoride trihydrate in dimethylformamide without any side reaction; this new Trp(Ppt) derivative is successfully applied to the synthesis of bradykinin potentiating peptide 5a by the solution method, as well as by the solid phase method using a fluoride ion deprotection method.