Crystal Structure of the N-Benzyloxycarbonyl-alanyl-phenylalanyl-methyl Ester: The Importance of the H-Bonding Pattern

Large crystals of the methyl ester of the N-a-benzyloxycarbonyl protected Ala-Phe dipeptide (Z-AF-OMe) were obtained after the very slow evaporation of a solution of the corresponding carboxylic acid (Z-AF-OH) in methanol containing an excess of HCl. The structure was confirmed by single crystal X-ray diffraction data. It crystallizes in the orthorhombic space group P2 12 12 1 with unit cell dimensions a = 5.0655(6) ？, b = 8.4614(8) ？, c = 46.856(5) ？, V = 2008.3(4) ？ 3, Z = 4. In the crystal, the molecules form hydrogen bonded chains running along the a axis of the unit cell. Other secondary interactions are also discussed.