Phosphinyl- and Phosphinothioylamino Acids and Peptides. IV. Further Examples of Use of the Diphenylphosphinothioyl Group for the Protection of Amino Acids

Abstract
The preparation and purification of diphenylphosphinothioyl(Ppt)-amino acids were studied. The side-chain functional groups of tyrosine and cysteine were found to react also with diphenylphosphinothioyl chloride to form O-Ppt and S-Ppt derivatives. Acidic reagents for the removal of N-Ppt group were examined by using N,O-bis-Ppt-tyrosine ethyl ester (III) as the most difficult model, HCl in HCO2H–CH2Cl2 being found to be most preferable. The O- and S-Ppt bonds were stable during the course of acidic treatments, but could be removed by alkaline hydrolysis. An application of Ppt-amino acids to the solid phase peptide synthesis is given.
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