The p-(Methylsulfinyl)benzyl Group: A TFA-Stable Carboxyl-Protecting Group Readily Convertible to a TFA-Labile Group

Article abstract of DOI:10.1021/jo00238a016

The p-(methylsulfinyl)benzyl or Msib ester is recommended as a selectively cleavable carboxyl-protecting group for peptide synthesis.Peptide oramino acid esters of p-(methylsulfinyl)benzyl alcohol, HO-Msib (2), or p-(methylthio)benzyl alcohol, HO-Mtb (1), are readily prepared from the corresponding alcohols or alkyl halides.Msib esters may also be obtained from Mtb esters by oxidation with m-chloroperbenzoic acid.Msib esters are readily deoxygenated by excess Me3SiCl/Ph3P, Me3SiCl/Me2S, or anhydrous hydrogen chloride.Msib esters are exceedingly stable to TFA while Mtb esters solvolyze rapidly.A sample peptide synthesis demonstrates the protection of the C-terminal carboxyl group during synthesis as the Msib ester followed by Msib group removal on completion of synthesis by deoxygenation and TFA solvolysis.The stability of Mtb and Msib esters to typical acid conditions of peptide synthesis is described.The stability of Msib esters to various peptide synthesis conditions suggests that the Msib group should be quite useful as a carboxyl-protecting group in peptide synthesis.