Diastereoselective 14β-Hydroxylation of Baccatin III Derivatives
摘要:
14beta-Hydroxybaccatin III, a compound with limited availability by natural sources, is the starting material for the synthesis of the second-generation anticancer taxoid ortataxel. The 7-tertbutoxycarbonyl. (1a) and 7-triethylsilyl (1b) derivatives of 14beta-hydroxybaccatin III 1,14-carbonate were synthesized from 10-deacetylbaccatin III (3). The crucial steps were (a) the C(14)beta hydroxylation of the corresponding 13-oxobaccatin III derivatives by oxaziridine-mediated electrophilic oxidation and (b) the reduction of the C-13 carbonyl group with sodium or alkylammonium borohydrides. This protocol provides a practical way for the semisynthesis of ortataxel from 10-deacetylbaccatin III, a compound readily available from various yews.
Two novel 5(20)-thia analogues of docetaxel have been synthesized from 10-deacetylbaccatin III or taxine B and isotaxine B. The key step of these syntheses is the concomitant thietane ring formation and acetylation of the tertiary alcohol at C-4. Both compounds are less cytotoxic than docetaxel but have divergent activity on microtubule disassembly.
Baccatin III derivatives: Reduction of the C-11, C-12 double bond
Zinc-promoted reduction of 13-oxobaccatin III derivatives leads to 11,12-dihydro analogs. The reduced products are unstable and a skeleton rearrangement occurs leading to the cleavage of the C-10, C-11 bond. The 11,12-dihydrobaccatin III derivatives do not retain antitubulin activity.
5(20)Deoxydocetaxel was prepared from 13-oxo-10-deacetyl baccatin III. This compound is the first docetaxel analogue with a modified D-ring which is as active as paclitaxel on microtubules. (C) 2000 Elsevier Science Ltd. All rights reserved.