title: Absolute configuration of natural diastereoisomers of 6beta-hydroxyhyoscyamine by vibrational circular dichroism.
abstract: The absolute configuration of the two natural diastereoisomers of 6beta-hydroxyhyoscyamine has been determined using vibrational circular dichroism (VCD) spectroscopy. The predicted VCD and IR spectra of (3R,6R,2'S)-6beta-hydroxyhyoscyamine (1) and (3S,6S,2'S)-6beta-hydroxyhyoscyamine (2) were calculated using density functional theory (DFT) with the B3LYP functional and 6-31G(d) basis set and considering the eight lower energy conformations of each diastereoisomer. In both cases, the first four conformers showed the N-Me group in the syn orientation, permitting the formation of a hydrogen bond between the hydroxy group at the tropane ring and the tertiary nitrogen atom. In addition the eight conformers showed an intramolecular hydrogen bond between the hydroxy and carbonyl groups of the tropic ester moiety. The calculated IR spectra of both molecules showed good agreement with the experimental spectra, while comparison of the experimental and calculated VCD spectra showed that the absolute configuration of dextrorotatory 6beta-hydroxyhyoscyamine is (3R,6R,2'S), while the levorotatory isomer is (3S,6S,2'S).
authors.affiliation: Departamento de Química, Facultad de Ciencias, Universidad de Chile, Casilla 653, Santiago, Chile.
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Muñoz
authors.forename: Orlando
authors.initials: O
authors.lastname: Muñoz
authors.forename: Pedro
authors.initials: P
authors.lastname: Joseph-Nathan
mesh_terms: D002942:Circular Dichroism; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D012991:Solanaceous Alkaloids / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D012991:Solanaceous Alkaloids; C003922:anisodamine