Taxol or paclitaxel is a diterpenoid pseudoalkaloid first obtained from the bark of North American Taxus species Taxus brevifolia Nutt (Pacific Yew). Family: Taxaceae

Common Names

English: Yew tree – Pacific yew, Himalayan yew

Hindi: Barmi, Talispatra

Commercial Importance

Leaves, twigs, bark and roots of Taxus species contain a unique class of diterpenoid alkaloids called taxanes that are a source of taxol, a chemotherapeutic drug used to treat a range of human cancers. Discovered by the US National Cancer Institute (NCI) in the bark of Pacific Yew, paclitaxel was brought to the market under the trade name ‘Taxol’ by the pharmaceutical company Bristol Meyers Squibb. The number of paclitaxel manufacturers and those of other taxane-based drugs has expanded in recent years. Taxanes are structurally related to the toxic constituents found in the stem bark, leaves, roots and needles of other Taxus species including T.wallichiana (Himalayan yew). Over 100 taxanes have been characterized from Taxus species and taxol is a member of a small group of compounds possessing a four-membered oxetane ring and a complex ester side chain in their structures both of which are essential for anti-tumour activity.

Constituents

Taxol is found predominantly in the bark in relatively low amounts (0.01%–0.02%). Upto 0.033% of taxol has been recorded in some samples of leaves and twigs, but generally it is much lower than in the bark. Significant variation in the taxol content depending on season, geographical location and environmental factors as well as individual population of trees has been noted. The content of some other taxane derivatives in the bark is considerably higher, e.g., upto 0.2% baccatin III. Other taxane derivatives characterized include 10-deacetyl taxol, 10- deacetyl baccatin III (10-DAB), cephalomannine and 10-deacetyl cephalomannine.