Structure and conformation of the sodium chloride salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H2O)

The structure and conformation of the salt of N-t-Boc-Phenylalanyl-Proline (Boc-Phe-Pro·NaCl) (C₁₉H₂₆N₂O₅NaCl) (compound 2) and the dihydrate of N-t-Boc-Tyrosyl-Proline (Boc-Tyr-Pro·2H₂O) (C₁₉H₃₀O₈N₂) (compound 1) have been investigated with X-ray crystallographic and spectroscopic methods. Boc-Phe-Pro·NaCl crystallizeds in an extended trans conformation in the space groupP2₁ with cell dimensionsa=7.961 (3),b=10.045(2), andc=13.495(4). One intermolecular hydrogen bond and one intramolecular hydrogen bond was observed for the dipeptide salt. Boc-Tyr-Pro·2H₂O crystallized in an extended trans conformation in the space group P2₁ with cell dimensionsa=7.964(1),b=10.011(1), andc=13.853(2). Six intermolecular hydrogen bonds were observed for Boc-Tyr-Pro·2H₂O. The conformation of both dipeptides reflect collagen-type of proline-compounds. The puckering mode of the pyrrolidine ring of the proline residues can be described as an approximate C₂ half-chair symmetry having an A conformation with the Cγ atom located exo and Cβ atom located endo relative to the carboxamide group, i.e., γ/β T.Cis-trans isomerism was observed in the NMR spectra of both dipeptides with a predominance for the extended side chain for the phenylalanyl and tyrosyl residues, respectively.