Two novel 5(20)-thia analogues of docetaxel have been synthesized from 10-d
eacetylbaccatin III or taxine B and isotaxine B. The key step of these synt
heses is the concomitant thietane ring formation and acetylation of the ter
tiary alcohol at C-4. Both compounds are less cytotoxic than docetaxel but
have divergent activity on microtubule disassembly.