Collect. Czech. Chem. Commun. 2006, 71, 368-386

Conformation Study of A-Ring in 19β,28-Epoxy-2-fluoro-18α-oleananes

Iva Tišlerováa,*, Václav Richtrb and Jiří Klinota

a Department of Organic Chemistry, Faculty of Science, Charles University, Hlavova 2030, 128 40 Prague 2, Czech Republic
b Department of Chemistry, University of West Bohemia, 306 19 Plzeň, Czech Republic


A series of 2-fluoro-substituted 19β,28-epoxy-18α-oleanane triterpenoids was prepared. Detailed NMR analysis (1H, 13C, 19F) was used for independent determination of the configuration of substituents. Conformation of the A-ring was derived from coupling constants J(H,H), J(F,H), J(F,C) and NOE-contacts observed in 2D-H,H-NOESY spectra. It was found that A-ring in all 2α-fluoro derivatives 2-5 and 2β-fluoro-3β-OR derivatives 10 and 11 adopts chair-form, while in 2β-fluoro ketone 9 a boat-form is preferred. The chair-boat equilibrium of A-ring was found in 2β-fluoro-3α-OR derivatives 7 and 8.

Keywords: Triterpenes; Triterpenoids; 18α-Oleanane; NMR spectroscopy; Coupling constants; Conformation analysis; NOESY.

References: 22 live references.