title: NMR assignments and X-ray diffraction spectra for two unusual kaurene diterpenes from Erythroxylum barbatum.
abstract: The structural characterization of two new, unusual kaurene diterpenes isolated from roots of Erythroxylum barbatum is described. 1D NMR and several 2D shift-correlated NMR pulse sequences (1H,1H-COSY, HMQC, HMBC and NOESY) were used for structure elucidation and the unambiguous 1H and 13C chemical shifts assignments. Single crystal X-ray diffraction analysis was also used to confirm the final relative configuration of the compounds possessing the C-20 methyl and the CH2-15 methylene groups in cis-orientation.
authors.affiliation: Curso de Pós-Graduação em Química Orgânica, Departamento de Química Orgânica e Inorgânica, Centro de Ciências, Universidade Federal do Ceará, CP 12 200, Fortaleza-CE, 60451-970, Brazil.
authors.forename: Claudio Costa
authors.initials: CC
authors.lastname: dos Santos
authors.forename: Mary Anne
authors.initials: MA
authors.lastname: Sousa Lima
authors.forename: Raimundo
authors.initials: R
authors.lastname: Braz-Filho
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: de Simone
authors.forename: Edilberto Rocha
authors.initials: ER
authors.lastname: Silveira
mesh_terms: D045786:Diterpenes, Kaurane / Q000737:chemistry*; D030921:Erythroxylaceae / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D014961:X-Ray Diffraction
chemical_list: D045786:Diterpenes, Kaurane; C002627:kaurene