STRUCTURE OF CEFADROXIL MONOHYDRATE

7-[Amino(4-hydroxyphenyl)acetamido]-3-methyl-8-oxo-5-thia-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid monohydrate, C16H17N3O5S.H2O, M(r) = 381.41, orthorhombic, P2(1)2(1)2(1), a = 11.038 (5), b = 11.211 (6), c = 14.436 (8) angstrom, V = 1787 (2) angstrom3, Z = 4, D(x) = 1.419 g cm-3, lambda(Cu K-alpha) = 1.5418 angstrom, mu = 19.13 cm-1, F(000) = 800, T = 295 K, R = 0.039 for 1321 reflections with 1 greater-than-or-equal-to 2-sigma(I). Cefadroxil exists as a zwitterion and assumes a folded conformation as in the other beta-lactam compounds containing the 7-beta-phenylglycyl side chain. The amino atom N(18) is close to the exocyclic amide O(16) [2.718 (6) angstrom] but there is no intramolecular hydrogen bond. Instead, these two atoms are linked by hydrogen bonds mediated by a water molecule. There is a hydrogen bond between the phenolic O(25) and carboxyl O(12) atoms in the molecule, related by a translation along the a axis [O...H...O, 2.811 (5) angstrom]; H(25) is disordered between these two atoms as observed in amoxycillin trihydrate. The crystal packing consists of an intricate hydrogen-bonding network.