Conserved and novel structural characteristics of enantiomorphic Leu‐enkephalin

The crystal of the Leu-enkephalin racemate (L-Tyr-Gly-Gly-L-Phe-L-Leu and D-Tyr-Gly-Gly-D-Phe-D-Leu) was obtained as a centrosymmetric space group. Crystal data: C28H37N5O7 x 1.5H2O, Mw = 582.6, triclinic, space group P1, a = 11.176(3), b = 16.115(3), c = 10.204(4) A, alpha = 92.41(3), beta = 104.86(2), gamma = 85.35(2)degrees, V = 1770(1)A3, Z = 2; F(000) = 640, mu(CuK alpha) = 6.50 cm-1, D chi = 1.081 g cm-3. The structure was determined by X-ray diffraction. The conformation of the Leu-enkephalin racemate was classified into the extended form which has been often observed in natural enkephalin. The symmetry-related molecules were connected by hydrogen bonds and arranged in an antiparallel fashion. The molecular packing showed a sheet structure similar to that of natural enkephalin.