title: Molecular and crystalline structures of three (S)-4-alkoxycarbonyl-2-azetidinones containing long alkyl side chains from synchrotron X-ray powder diffraction data.
abstract: The (S)-4-alkoxo-2-azetidinecarboxylic acids are optically active beta-lactam derivatives of aspartic acid, which are used as precursors of carbapenem-type antibiotics and poly-beta-aspartates. The crystal structures of three (S)-4-alkoxo-2-azetidinecarboxylic acids with alkyl chains with 10, 12 and 16 C atoms were solved using parallel tempering and refined against the X-ray powder diffraction data using the Rietveld method. The azetidinone rings in the three compounds display a pattern of asymmetrical bond distances and an almost planar conformation; these characteristics are compared with periodic solid-state, gas-phase density-functional theory (DFT) calculations and MOGUL average bond distances and angles from the CSD. The compounds pack along [001] as corrugated sheets separated by approximately 4.40 A and connected by hydrogen bonds of the type N-H...O.
authors.affiliation: Laboratorio de Cristalografía, Departamento de Química, Facultad de Ciencias, Universidad de Los Andes, Mérida 5101, Venezuela.
authors.forename: Luis E
authors.initials: LE
authors.lastname: Seijas
authors.forename: Asiloé J
authors.initials: AJ
authors.lastname: Mora
authors.forename: Gerzon E
authors.initials: GE
authors.lastname: Delgado
authors.forename: Francisco
authors.initials: F
authors.lastname: López-Carrasquero
authors.forename: María E
authors.initials: ME
authors.lastname: Báez
authors.forename: Michela
authors.initials: M
authors.lastname: Brunelli
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Fitch