title: 5-Dethia-5-oxacephams: toward correlation of absolute configuration and chiroptical properties.
abstract: The relationship between chiroptical properties of differently substituted 5-dethia-5-oxacephams and their respective molecular structures was investigated. The amide chromophore of the beta-lactam unit in these compounds was found to be nonplanar with a shallow pyramidal configuration at the nitrogen atom. Due to the nonplanarity, the beta-lactam system becomes inherently dissymmetric, which is supported by a high magnitude of the n --> pi* CD band. It was also found that the helicity of the lactam moiety in investigated oxacephams is controlled by the absolute configuration at the C(6) carbon atom. On this basis, a helicity rule correlating a positive (negative) sign of the n right arrow pi Cotton effect with a negative (positive) O [double bond] C [bond] N [bond] C(6) torsional angle for policyclic beta-lactam derivatives possessing a nonplanar amide chromophore was formulated.
authors.affiliation: Institute of Organic Chemistry of the Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland.
authors.forename: Robert
authors.initials: R
authors.lastname: Łysek
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Borsuk
authors.forename: Marek
authors.initials: M
authors.lastname: Chmielewski
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Kałuza
authors.forename: Zofia
authors.initials: Z
authors.lastname: Urbańczyk-Lipkowska
authors.forename: Agata
authors.initials: A
authors.lastname: Klimek
authors.forename: Jadwiga
authors.initials: J
authors.lastname: Frelek
mesh_terms: D000900:Anti-Bacterial Agents / Q000138:chemical synthesis / Q000737:chemistry*; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D019818:Clavulanic Acid / Q000737:chemistry; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry; D008968:Molecular Conformation; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D065093:beta-Lactamase Inhibitors
chemical_list: D000900:Anti-Bacterial Agents; D004791:Enzyme Inhibitors; D065093:beta-Lactamase Inhibitors; D019818:Clavulanic Acid