The crystal and molecular structure of (2-Hydroxyphenyl) alanine (o-Tyrosine).

The crystal structure of D,L-(2-hydroxyphenyl)-alanine has been determined by X-ray methods using 1971 observed reflections. The crystals are monoclinic, space group P2-1, with four molecules in the unit cell of dimensions a=6.32-5 A; b=26.48-9 A; c=5.36-7 A, and beta=98.1-8 degrees. The structure was solved by direct methods and refined to a conventional R-factor of 0.048; estimated standard deviations in bond lengths not involving hydrogen are 0.002-0.004 A and in angles 0.1-0.2 degrees. Bond lengths and angles are in accordance with those found in tyrosine. Owing to an intra-molecular hydrogen bond between the ammonium group and the ring hydroxyl oxygen atom, however, the conformational angles differ from those found in several other phenylalanine derivatives. There are non-crystallographic centres of symmetry between pairs of enantiomeric molecules.