B Ring and Its Substitutions

Generally, C-10 deacetylation or deoxygenation made an insignificantly negative and positive contribution to the cytotoxicity against sensitive tumor cells, respectively, by comparison with paclitaxel. 

Datta et al. synthesized 10-epi and 9a-OH paclitaxel analogs by iterative oxidation-reduction transformations, furnishing 39-41. lO-Epi pachtaxel 39a and 10-deacetyl paclitaxel 39b are slightly more active than pachtaxel in both cytotoxicity and tubuhn binding assays, whereas their 9(R) counterparts 40 are comparable 

Walker et al prepared lOa-spiro epoxide (42a) and its 7-methoxymethyl (MOM) ether (42b), which exhibited comparable cytotoxicity and tubulin assembly activity with paclitaxel. 

When the C-9 keto group in paclitaxel was replaced by hydroxyl, either a or p-OH analogs displayed slightly higher potencies. The 9a-OH, that is, 9(f )-OH, analog of 

A series of 9-deoxy analogues was prepared from 13-acetyl-9(/f)-OH-baccatin III (44) by an Abbott Lab group. They found that the 9-deoxypaclitaxel 52a 

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