Five Novel Taxanes from Taxus canadensis

Five novel taxanes (1−5) have been isolated from the needles of Taxus canadensis, and their structures were elucidated on the basis of spectroscopic data. Two of these taxanes have structural features seldom found in yews, with 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, differing mostly in the location of the double bond in ring A, were compared. The different conformation of ring A derived from the C-12, C-13 double bond is particularly interesting because it implies that if a Taxol (paclitaxel) side chain were attached to C-13 it would have a different orientation from that in paclitaxel.