Fmoc-Tyr(tBu)-Ser(Psi(Me,Me)pro)-OH is mainly used in peptide synthesis. It consists of a dipeptide in which the serine residue has been reversibly protected as a structure-damaging proline-like TFA-labile oxazolidine. The reason for introducing the pseudoproline residue as a dipeptide is that it avoids the acylation of the hindered oxazolidine nitrogen. This has the added advantage of extending the peptide chain by two residues in a single step. The serine residue is regenerated in the normal trans fatty acid mediated cleavage reaction.
