A model compound for poly(ester amide)s: diethyl-3,9-diaza-4,8-dioxoundecanedioate

The compound diethyl-3,9-diaza-4,8-dioxoundecanedioate (EtGGGEt) has crysta llized in the space group P2(1) with cell parameters a = 8.267(2), b = 4.85 3(4), c = 20.361(6) Angstrom, beta = 97.96(2)degrees. The crystal structure has been solved by direct methods and refined using the full matrix least squares methodology. There is one molecule in the asymmetric unit, in spite of its symmetric constitution. The central part of the molecule, the gluta ramide moiety, has a partial folded conformation (T (S) over bar TTST), whi ch differs from the all trans conformation found in related moieties but wi th an even number of carbon atoms. The two flanking glycine residues have a different conformation one from each other; the first one adopts the stand ard conformation (psi = -156.5 degrees, phi = 73 degrees), while the second one has an unusual conformation. In this glycine the oxygen atom has a big temperature factor and it is disordered in two positions. Both facts, conf ormation and disorder of the second glycine, seem to be due to improvement of contacts with neighboring molecules. The molecules are hydrogen bonded a long the b axis, forming infinite rows with the same sense of orientation, so the crystal has a polar structure.