Tyrosinium-D-tetrahydroisoquinoline-3-carboxylate 1.5-hydrate and tyrosyl-D-tetrahydroisoquinoline-3-carboxamide hydrate.

Crystals of the two dipeptide title compounds, Tyr-D-Tic, C19H20N2O4.1.5H2O, and Tyr-D-Tic-NH2, C19H21N3O3.H2O, were prepared by the sitting-drop method. Tyr-D-Tic is orthorhombic (P2(1)2(1)2(1)) and crystallizes as a zwitterion. The asymmetric unit contains two peptide molecules and three molecules of water. Tyr-D-Tic-NH2 crystals are monoclinic (P2(1)), the asymmetric unit containing one peptide molecule and one molecule of water. Despite some differences in packing, the conformation of the two dipeptides is almost identical (r.m.s. deviation for non-H atoms is approximately 0.18 A).