Oxygenated verticillene derivatives from Bursera suntui

Four verticillane derivatives were isolated from Bursera suntui. Their structures, stereochemistry and conformational preferences were evaluated by DFT molecular modeling in combination with NMR measurements including NOESY correlations. Medium polarity fractions of the hexane extracts of the stems of Bursera suntui afforded six previously known ( 1– 6) and four hitherto unknown verticillane derivatives: (1 S,3 Z,7 S,8 S,11 S,12 S)-(+)-7,8-epoxyverticill-3-en-12,20-diol ( 7), (1 S,3 Z,7 S,8 S,11 S,12 S)-(+)-7,8-epoxyverticill-3-en-12,20-diol 20-acetate ( 8), (1 S,3 Z,7 S,11 S,12 S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol ( 9), and (1 S,3 Z,7 S,11 S,12 S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol 20-acetate ( 10). Acetylation of 9 and 10 yielded (1 S,3 Z,7 S,11 S,12 S)-(+)-verticilla-3,8(19)-dien-7,12,20-triol 7,20-diacetate ( 11), while hydrolysis of 8 gave 7. The structures and stereochemistry of 7– 11 were established by spectroscopic analyses, particularly by 1D and 2D NMR spectra and HRESIMS. The conformational preferences of 7– 11 were studied by molecular mechanics modelling employing the Monte Carlo protocol followed by B3LYP/DGDZVP DFT calculation, thus supporting the observed 1H NMR NOESY cross peaks.