Pseudoproline a powerful tool for improving the quality of synthetic peptides. Pseudoproline dipeptides have greatly increased the success rate for synthesizing both long and difficult peptides. Pseudoproline dipeptides can be introduced in the same manner as other amino acid derivatives. The routine use of pseudoproline (oxazolidine) dipeptides in the FMOC solid phase pepdide sysnthesis (SPPS) of serine- and threonine-containing peptides leads to remarkable improvements in quality and yield of crude products and helps avoid unnecessary repeat synthesis of failed sequences. Pseudoproline dipeptides have proven particularly effective in the synthesis of intractable peptides, long peptides/small proteins, and cyclic peptides, enabling in many cases the production of peptides that otherwise could not be made. These dipeptides are extremely easy to use: simply substitute a serine or threonine residue together with the preceding amino acid residue in the peptide sequence with the appropriate pseudoproline dipeptide. The native sequence is regenerated on cleavage and deprotection.
Peter White, John W. Keyte, Kevin Bailey, Graham Bloomberg. Expediting the Fmoc solid phase synthesis of long peptides through the application of dimethyloxazolidine dipeptides. Journal of Peptide Science Volume 10, Issue 1, pages 18–26, January 2004.