2 The structural elucidation of taxoids

Abstract

This chapter presents structural elucidation of taxoids. The structural elucidation of taxoids can be carried out using a variety of spectral methods, especially nuclear magnetic resonance (NMR) techniques. Mass spectroscopy (MS) of taxoids has been used to obtain information on the molecular weight and to identify the acyl groups bound to the diterpenoid core. The most important chromophore in the diterpenoid moiety of taxoids is the enone system found in compounds of the 10- and 13-oxo-Δ 11 type. In taxanes, these systems can be distinguished on the basis of UV data. The absolute configuration at C-1 of taxoids is opposite to the one found in their alleged biogenetic precursors isolated so far from plants. The shape of the diterpenoid core of taxoids is dictated mainly by the conformation of ring B. More than one conformation is possible for ring B, except in 3,11-cyclotaxanes, where the presence of a transannular bond prevents conformational mobility.