Dipeptides containing serine and threonine derived oxazolidines are prepared by reacting side chain unprotected dipeptides containing C-terminal Thr or Ser with dimethoxypropane. The resulting building blocks can be coupled in Fmoc-based solid phase peptide synthesis enhancing peptide solvation by its secondary structure disrupting potential. The present procedure may be considered as a first step towards a reversible modification of structural and functional properties of bioactive peptides and proteins.