NMR and molecular modeling study of active and inactive taxol analogues in aqueous and nonaqueous solution

The conformations of the biologically active taxol analogs Taxotere®, 3R, 4R, and 4S, and the biologically inactive analog 3S were evaluated in CDCl 3 and DMSO–water solution using 1 H NMR coupling constant and NOESY data and molecular modeling. The solution structures of Taxotere® were very similar to those detected previously for taxol. The A-ring side chain conformations of analogs 3 and 4 could not be defined with the same precision as had been possible for taxol, but the conformational possibilities could be significantly limited by the data. Analogs 3R, 4R, and 4S (but not 3S) can mimic the dominant conformation of taxol in chloroform, but no logical relationship between biological activity and aqueous solution conformation could be detected.