CRYSTAL-STRUCTURE OF A TRIPEPTIDE, GLYCYL-D, L-LEUCYL-L, D-ALANINE

The crystal structure of a tripeptide, glycyl-D, L-leucyl-L, D-alanine has been determined by X-ray methods and refined to a final R-index o f 0.079. There are two crystallographically independent molecules in a monoclinic unit cell with a = 17.817(2), b = 10.276(2), c = 18.451 (3 )angstrom, beta = 116.95 (3), Z = 8 and space group P2(1)/n. Both the molecules exist as zwitterions and adopt essentially similar conformat ion, with the backbone folding characteristic of a type II reverse tur n. Even the leucyl side chains assume essentially similar conformation in the two independent molecules. The packing of the molecules involv es spatial segregation of the leucyl side chains.