ß-olded crystal structures of two dipeptides deriving from the L-PRO-L-CYS sequence

The molecular structures of tBuCO-L-Pro-L-Cys-NHMe (ßl-tum) and tBuCO-L-Pro-L-Cys(StBu)-NHiPr (ßll-tum) have been solved by X-ray diffraction experiments. There is no intramolecular interaction involving the Cys-S atom in either of these two dipeptides, but an intermolecular S...0 distance of 3.91 Å is found in the former derivative. These two crystal structures confirm that both ßl and ßll - tum conformations are accessible to homochiral dipeptide sequences