Five novel taxanes from Taxus canadensis

Five novel taxanes (1-5) have been isolated from the needles of Taxus canad ensis, and their structures were elucidated on the basis of spectroscopic d ata. Two of these taxanes have structural features seldom found in yews, wi th a C-12, C-13 double bond and a hydroxymethylene at C-4. In addition, the 2D structures generated by molecular modeling of taxanes 1 and 2, differin g mostly in the location of the double bond in ring A, were compared. The d ifferent conformation of ring A derived from the C-12, C-13 double band is particularly interesting because it implies that if a Taxol (paclitaxel) si de chain were attached to C-13 it would have a different orientation from t hat in paclitaxel.