Crystal and molecular structure of allo-4-hydroxy-L-proline dihydrate

Abstract

allo-4-Hydroxy-L-proline crystallizes from an aqueous solution as the dihydrate. The crystals are orthorhombic, space grooup P2,2,2 with a=7.08(2), b=22.13(3), c=5.20(2) Å. The structure was solved by direct methods and refined by block-diagonal least swuares. The final R for 733 observed reflexions is 0.054. The molecule exists as a zwitterionl with hydroxyl and carboxy groups eis to the pyrrolidine ring. The latter is puckered at the β-carbon atom, which deviates by -0.54 Å from the best plane formed by the four remaining atoms. The moleules are held together by a network of hydrogen bonds, the water molecules playing a dominant role in the stability of the structure.