title: 1H and 13C NMR spectral assignments and conformational analysis of 14 19-nor-neoclerodane diterpenoids.
abstract: Unambiguous and complete assignments of 1H and 13C NMR chemical shifts for 14 19-nor-neoclerodane diterpenoids, nine of them isolated from natural sources and five other synthetic derivatives, are presented. The assignments are based on 2D shift-correlated (1H,1H-COSY, 1H,13C-gHSQC and 1H,13C-gHMBC) and NOE experiments. The conformations of rings A and B of these compounds are supported by the 3J(H,H) values and they agree with the low-energy conformations obtained by semi-empirical calculations. Moreover, the data obtained in this work for 2-acetoxyteucvidin and a semisynthetic 18-aldehyde derivative indicate that the configuration at C-2 of the former and at C-10 of the latter must be reversed with respect to those reported previously.
authors.affiliation: Instituto de Química Orgánica, CSIC, Juan de la Cierva 3, E-28006 Madrid, Spain. iqor107@lqog.csic.es
authors.forename: Benjamín
authors.initials: B
authors.lastname: Rodríguez
authors.forename: María L
authors.initials: ML
authors.lastname: Jimeno
mesh_terms: D001572:Benzofurans / Q000032:analysis / Q000737:chemistry*; D002247:Carbon Isotopes; D004224:Diterpenes / Q000032:analysis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons
chemical_list: D001572:Benzofurans; D002247:Carbon Isotopes; D004224:Diterpenes; D011522:Protons; C087913:neocnidilide