Synthesis and Crystal Studies of Novel 11,12-Dihydro-Taxoids Derived from 1-Deoxybaccatin VI

Two novel taxoids were synthesized from 1-deoxybacctin VI (1) and their crystal structures were determined by X-ray crystallographic techniques. The influence of the 11,12-olefin of the tetracyclic moiety on molecular conformations were investigated. Comparison to other baccatin analogs, a larger effect on the conformation of the diterpenoid core is observed when the 11,12-olefin is reducted. Conformational analysis show that the reduction of the 11,12-olefin has a decisive influence on the conformation of the A and B ring. Compounds 3 and 5 crystallize in orthorhombic system, space group P2₁2₁2₁. In the structure of compound 3, the six-membered A ring exhibits the 1,3-diplanar boat conformation, the eight-membered B ring adopts a boat–chair conformation, and the six-membered C ring exhibits a slightly distorted half-chair conformation. However, in 11,12-dihydro-taxoids 5, the six-membered A ring exhibits a chair conformation and the conformation of the eightmembered B ring has a large distortion.

Graphical Abstract

The synthesis of novel 11,12-dihydro-taxoids from 1-deoxybacctin VI are presented, in which the crystal structure of the compound 5 was characterized.