Taxine B (3), iso lated from th e d ried needles of Taxus baccata, w as converted into six novel 7-deoxypaclitaxel analogs, 2 0 , 2 1 a ,b , a n d 2 3 -2 5 , th a t have s tru c tu ra l changes a t C l, C2, and C4. A m ethod for th e in tro d u c tio n of th e benzoyl function a t C2, v ia a benzylidene acetal a t C l -C2, will be revealed. A ll com pounds show ed very little or no m easu rab le cytotoxic activity against some w ell-characterized h u m a n tu m o r cell lines, probably due to th e nonacylated hydroxyl group a t C4.The diterpenoid p aclitax el (1) (C h a rt 1), firs t isolated by W ani and W all1 from th e b a rk of th e w e ste rn yew Taxus brevifolia, is a new a n d v ery prom ising a n titu m o r com pound.2 The s tru c tu ra l com plexity of (1), and its unique m echanism of actio n ,3 h av e stim u la te d extensive research toward th e sy n th esis of paclitaxel as w ell as th e synthesis of new analogs. U n til recen tly , th e synthesis of paclitaxel has been achieved b o th by sem isy n th esis,4 s ta rtin g from 10-deacetylbaccatin III (2) (C h a rt 1), an d by to ta l synthesis.5 T he synthesis of analogs for s tru c tu re -activity rela tionship (SAR) studies have m ostly been accom plished by stru ctu rally m odifying p aclitax el itself.6 In several cases, precursors, such as b a c c a tin I I I ,7 brevifoliol,8 13-acetyl-9-dihydrobacatin I I I ,9 a n d 14-/M iydroxy-10-desacetylbaccatin,10 iso lated from th e needles of different Taxus species, w ere used.
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