The Crystal Structure of Dimethyl (2Z,6Z)-2,7-bis-(benzyloxycarbonyl-amino)octa-2,6-diendioate: A Useful Precursor for Optically Pure 2,7-Diaminosuberic Acid

Needle shaped single crystals of the dimethyl ester of (2Z,6Z)-2,7-bis-(benzyloxycarbonyl-amino)-octa-2,6-diendioic acid (1), C26H28N2O8 were obtained by very slow cooling from methanol/ethylacetate solution 20:1. 1 crystallizes in the anorthic space group P`1 (No. 2) with a=4.813(5), b=12.277(6), c=12.340(7)Ä, alpha=117.15(3)?, ß=97.52(4)?, gamma=92.02(4)?, Z=1. The crystal structure was determined from diffractometer data (MoK alpha-radiation). It was solved by direct methods and refined to a conventional R of 0.054 for 1452 Fo's and 178 refined parameters. The molecule is characterized by the presence of an inversion center. In the crystal structure the molecules are stacked along the crystallographic a-axis. In this direction - which coincides with the needle axis of the crystals - each molecule is connected with its neighbors through almost linear N-H...O-hydrogen bonds.