The crystal structure of dimethyl (2Z, 6Z)-2,7-bis-(benzyloxycarbonylamino)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-(be nzyloxycarbonyl- amino)-octa-2,6-diendioic acid (1), C26H28N2O8 were obtain ed by very slow cooling from methanol/ethylacetate solution 20:1. 1 crystal lizes in the anorthic space group P (1) over bar (No.2) with a = 4.813(5), b = 12.277(6), c = 12.340(7) Angstrom, alpha = 117.15(3)degrees, beta = 97. 52(4)degrees, gamma = 92.02(4)degrees, Z = 1. The crystal structure was det ermined from diffractometer data (MoK alpha-radiation). It was solved by di rect 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 in version center. In the crystal structure the molecules are stacked along th e crystallographic a axis. In this direction - which coincides with the nee dle axis of the crystals - each molecule is connected with its neighbors th rough almost linear N-H ... O-hydrogen bonds.