Taxanes with C-5-amino-side chains from the needles of Taxus canadensis

Taxanes and taxoids of the genus Taxus - A comprehensive inventory of chemical diversity

The pseudoalkaloid diterpene Taxol® (paclitaxel) emerged as a best-selling anti-cancer drug in the mid-1990s. The compound attracted considerable interest because of its unique mechanism to stabilize microtubules, thus reducing dynamicity and ultimately promoting mitotic arrest. Taxol was originally isolated from members of the genus Taxus. Over the last 50 years, close to 600 metabolites with taxane scaffolds were isolated from various Taxus species and their structures reported. The present review article provides an overview of the known chemical diversity of taxanes, with an emphasis on the functionalization of diterpene scaffolds. The implications of the occurrence of chemically diverse taxane metabolites for unraveling Taxol biosynthesis and enabling pathway engineering are discussed as well.

Chemical studies on Taxus canadensis

A series of new taxanes, 1-93, have been isolated, together with 37 known taxoids including Taxol(®) (paclitaxel) and cephalomannine, from the Canadian yew, Taxus canadensis (Taxaceae) in the past 30 years. These new taxoids possess various skeletons containing 5/7/6, 6/10/6, 6/5/5/6, 6/8/6, and 6/12 ring systems and six new taxanes with four novel skeletons, i.e., a taxane with a 6/6/8/6 ring system, a taxane with a [3.3.3] propellane skeleton, three taxanes with [3.3.3] [3.4.5] dipropellane sytems, as well as a novel taxane with a unique 5/5/4/6/6/6 hexacyclic skeleton, containing a unique [3.3.2] propellane, were isolated for the first time from natural sources. It should be emphasized that 13-acetyl-9-dihydrobaccatin III, a very useful starting material for the semisynthesis of Taxol(®) and Taxotere(®) , represents the most abundant taxane in the needles of this yew tree. These findings establish the above mentioned yew tree as significantly different from the remaining species. On the other hand, some chemical modifications on the taxanes isolated from this plant were carried out.

First example of conformational exchange in a natural taxane enolate

A detailed NMR study and full assignments of the (1)H- and (13)C-NMR spectral data for a novel enolate taxane isolated from Taxus canadensis needles is described. The structures of two stable conformers were established using a combination of 1D and 2D NMR techniques including (1)H, (1)H-COSY, gs-HMQC, gs-HMBC, NOESY and T-ROESY. Ab initio quantum mechanical calculations were performed on the B3LYP/6-31G* level of basis set to assist the NMR findings.